From Leonard Susskind to Everyone:

A number of years ago I became aware of the large number of physics enthusiasts out there who have no venue to learn modern physics and cosmology. Fat advanced textbooks are not suitable to people who have no teacher to ask questions of, and the popular literature does not go deeply enough to satisfy these curious people. So I started a series of courses on modern physics at Stanford University where I am a professor of physics. The courses are specifically aimed at people who know, or once knew, a bit of algebra and calculus, but are more or less beginners.

The response was overwhelming and it was suggested that Stanford put them up on the internet. You can find them at

http://www.learnoutloud.com/Catalog/Science/Physics/Modern-Theoretical-Physics/23022

Since the videos went up, I have received many emails with good questions. Some are about the material in the courses. Some are more broadly about physics and science. Here is the place to ask them. If I know the answer to your question I will post it. If not perhaps someone else can answer.

Leonard Susskind

## Monday, April 21, 2008

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## 598 comments:

«Oldest ‹Older 201 – 400 of 598 Newer› Newest»HI sir , they way you teach is just magical and its so simple that every one is able to understand , currently am doing my masters in physics from Delhi University in India and the lectures have been of great help . However i have a request if there are more lectures of you on more advanced topics on quantum mechanics(perturbation theory and its application), stat mech (ensemble theory) , please make them available on Stanford channel at youtube . Even if u got lecture notes on net on these topics, it would be very nice.

I'm a retired high tech executive returning to physics as a hobby, based on a 40-year old BS degree in physics and a career in engineering and then management.

I just finished the lecture series on special relativity and classical field theory. I appreciate Dr. Susskind's dedication to teaching, his outreach to the public, his teaching skills to focus on essential points in order to communicate the core of the subject in a limited time, and his approach to teaching by using the real underlying and unifying themes of modern physics rather than just linking a patchwork of isolated subject modules. I look forward to working through the other series as well.

I'm writing to suggest additional educational online resources for the benefit of others and to seek help on a particular physics problem. Due to overall length, this will be done in two parts.

First, the additional resources.

I first found these lectures at www.freevideolectures.com/physics. Other lecturers from other institutions are there as well. Subjects other than physics are also covered. Some time ago, I discovered www.learner.org which exists primarily to train and support teachers. However, it also has a number of very well done lecture series. A particularly outstanding one for high school seniors and college freshmen is the award winning "The Mechanical Universe and Beyond" by Dr. Goodstein of CalTech. (I also enjoyed "The Western Tradition" by a UCLA professor covering western world history from the first agriculture in Mesopotamia to the Cold War. Mesmerizing.) In addition, the physics websites at CalTech and MIT have useful online course lecture notes and slides. To be honest, at MIT these varied from poor to excellent while those at CalTech were uniformly excellent. (I'm not affiliated with either school.) Some are clearly prototypes for future textbooks.

There is also a nonprofit, youth organization I want to highlight called Future Scientists and Engineers of America (FSEA). FSEA was founded here in Orange County, CA in 1989 and now has hundreds of local chapter nationwide. It targets grades 4-12 to foster learning and enthusiasm for math, science, engineering and other technical fields through projects and events in a club environment of age-appropriate, hands-on fun and activities among friends. Local industry and university speakers and tours add to the mix. These are school-sanctioned and supported after-school activities. FSEA is modeled after the long and highly successful Future Farmers of America (FFA), Girl Scouts and Boy Scouts. It now is also associated with the Discovery Science Center of Orange County, a major teaching museum. I recommend that individuals like yourselves consider supporting and even founding local chapters at schools in your area. More can be learned at www.discoverycube.org/fsea.aspx .

See Part Two.

Regards,

Tom Bartholet

Part Two

Now for the help I need with a physics problem.

Before doing Dr. Susskind's lecture series, I worked through Chapter 11 (Special Relativity) of Classical Electrodynamics (3rd Edition) by John David Jackson. As many of you know, this is the graduate student's bible on the subject. Having always been math oriented, I took a "no equation left behind" approach. I was able to derive every equation in the text of that chapter except one. I am absolutely stuck on trying to derive Equation (11.94) from Equations (11.92) and (11.93). Normally, Jackson withholds the details for the student to derive but writes in a manner similar to Edgar Allan Poe in the short story "The Purloined Letter", i.e., he hides the solution in plain sight. Not this time, despite what was intended as a helpful comment. I'm at a loss in dealing with the number e raised to a matrix power. If you Dr. Susskind or any of the many very capable readers of this blog can provide help, I would greatly appreciate it. My feeling is that this math technique will be important elsewhere as well. In return, I'll be happy to provide any of the derivations of other equations in the chapter text, provided I'm not doing someone's class homework.

A .pdf file may be the best format for that response, but I haven't seen how to attach a file to these comments. If necessary, I can be reached at my email address tbartholet@cox.net .

Best regards to all,

Tom Bartholet

Laguna Hills, CA

Dear Proffesor

Can Statistical Mechanics be applied to systems controled by contact forces like sand grains, rather than gases? Can you give me references for this applications.

Regards

William

Hi all,

a very simple question from me: If a graviton travels at the speed of light, how can it leave a black hole? In other words: If gravitons carry the gravitational forces, how could a black hole cause gravitation outside its horizon?

Best wishes from Germany,

Wolfgang.

DEAR LENNY, AT THE END OF LECTURE 4 GR YOU TALKED OF A METRIC OF AN EXPANDING SPACE TIME. THE FUNCTION BEING a(t). DOES THIS MEAN THAT THE SPEED OF LIGHT IS NO LONGER CONSTANT C=1, BUT DEPENDENT ON THE FUNCTION a(t)

DEAR LENNY, AT THE END OF LECTURE 4 GR YOU TALKED OF A METRIC OF AN EXPANDING SPACE TIME. THE FUNCTION BEING a(t). DOES THIS MEAN THAT THE SPEED OF LIGHT IS NO LONGER CONSTANT C=1, BUT DEPENDENT ON THE FUNCTIO a(t)

DEAR LENNY, AT THE END OF LECTURE 4 GR YOU TALKED OF A METRIC OF AN EXPANDING SPACE TIME. THE FUNCTION BEING a(t). DOES THIS MEAN THAT THE SPEED OF LIGHT IS NO LONGER CONSTANT C=1, BUT DEPENDENT ON THE FUNCTIO a(t)

DEAR LENNY, AT THE END OF LECTURE 4 GR YOU TALKED OF A METRIC OF AN EXPANDING SPACE TIME. THE FUNCTION BEING a(t). DOES THIS MEAN THAT THE SPEED OF LIGHT IS NO LONGER CONSTANT C=1, BUT DEPENDENT ON THE FUNCTIO a(t)

Dear Mr. Susskind, where can I find the correct solution of the twins paradox? Have you done some lectures on this topic or you can list me some link where I can find it?

Please, help me!

Carlo Pastore

Mechanical Engineer

Italy

Hi, I am very slowly working my way through Physics 101 with the help of a very qualified friend.

As I was learning vector addition an a-ha moment happened and began to wonder: Is anything still? Seems like everything, and I mean everything, is in motion. Hope I'm not wasting everyone's time, but the blog did say 'everyone'. I did enjoy Black Hole Wars and Briefer History of Time, but I sure have a long way to go.

Hi, Prof. Susskind. I'm not a scientist only a curious person about cosmology. So, I have a simple question that I hope you take your time to answer.

I know that c (speed of light) is the faster speed in the universe (nothing can travel faster than light). Nevertheless there are distant galaxies so far from our planet that its relative speed to us is faster than light (due the expansion of the universe). That's the reason why those galaxies are invisible to us.

I think it's no logical that an observer in that galaxy is getting away from us faster than light (the observer in that galaxy could think that WE are getting away from his planet at the speed of light). Maybe you could explain me what is really happening.

Something like that I think about the inflation at the begining of the universe, when space expanded itself faster than light in a tiny fraction of a second.

Best regards from Uruguay (South America)

Manuel Cicarello

Dr susskind,

can you please tell me about spontaneous symmetry braking ,

sir, in your lecture you have told about proper time as dτ^2 = dt^2-dx^2, but sir if τ represents time then left hand side will have dimensions of time as sec^2 but right hand side of the equation will have dimensions sec^2 – m^2,I can’t understand this because dimensions of any equations in physics must be same on both sides, please explain a bit.

Sir,

Your lectures in you tube are really very inspiring.Thanks a lot.

I have a question for clarification. Why an accelerated charged particle emits radiation?. I will be more satisfied if there is any rigorous mathematical treatment for the above phenomena.

I'm a student at Philip's Exeter Academy and have started watching your lectures on Special Relativity. Your lecture really show how beautiful physics is. Could you post some of the practive problems??

Thanks,

Stephen

The ordinary Feynman diagram for Compton scattering contains a single "virtual electron" state and this would at first seem to have no physical interpretation. But in the classical limit we recover Thomson scattering which is derived in classical electrodynamics by involving the oscillation of the electron which is (at least in principle) observable. My question is, what is the relation between this "virtual state" and the classical limit of the (in principle observable) electron oscillating back and forth? The momentum of the virtual state seems to not have a good interpretation in the classical limit, which I suppose is another subtlety of gauge invariance?

Dear professor Susskind,

You are really an amazing guy. Existence is full of surprises. One of which is having you here in our universe. I know you only want physics questions. But still. I am about to become 75 years old. I just followed and understood your first lecture on special relativity and still have a very long way to go to understand physics as it stands now. Obviously I do not have the time. How should I deal with this sate of limitation.

PS.I developed my own theory in the field of mind science together with a mathematician. It is called inhibition theory (see Wikipedia).

The "New Revoluyion In Particle Physics" lectures last posting on ITunes was lecture 5 of the Winter Term. When will the postings start up again?

dear professor susskind,

your videos have been really helpful!..thanks a lot for them!..if i am not wrong these lectures are for continuing education..what i want to say is it would be really helpful for millions of students if your lectures for graduate students were also uploaded.

thank you.

A question:

Classical mechanics. Angular movement

I couldn't reasonably understand why we take the derivative of Lagrangian with respect of r? Why not the time? (You have described the reason as "r" appearing in two instances, one is kinetic energy the other in potential) What logic leads us to that certain point? Trial error? or just the intention to get rid of "r"? I suppose not.. Or is mentioned calculation something that leads to a certain and desired answer?

ups.. Sorry I found the answer myself :/ Lagrangian is not time dependent and if it was energy would not be conserved..

Didn't delete my previous post, just in case someone has the same question.

Thanks

When will the 3rd quarter of "New Revolutions In Particle Physics" be posted to Itunes?

Hello from Canada, where we are anticipating the Queen's visit to the Perimeter Institute in Waterloo! Prof. Hawking is gave a speech from there earlier this month that was televised, and through it I learned about the black hole information paradox. I am delighted to have started reading your book on the subject. I apologize for not finishing the book first, but I am already so delighted by the first few chapters that I wanted to say hello and thankyou:)

Is there an equivalence between negative temperature and the addition of information. I'm thinking about ways of lowering entropy.

I am sorry for posting such a rudimentary question but I am fairly new to this level of Physics. Sir, whilst watching your videos on General Relativity(which I have not completed yet), I came upon the concept of contravariant vectors and covariant vectors. On digging a bit deeper I found out about one-forms an vectors(which is quite abstract to me). Nevertheless I could understand inner product at some level. Now that I have started Quantum Physics as well I have come across Hilbert space and bra-ket vectors.

My question is this: Are bra vectors one-forms an ket vectors vectors?

It would really help me if anyone could answer my question

Shounak

I am sorry for posting such a rudimentary question but I am fairly new to this level of Physics. Sir, whilst watching your videos on General Relativity(which I have not completed yet), I came upon the concept of contravariant vectors and covariant vectors. On digging a bit deeper I found out about one-forms an vectors(which is quite abstract to me). Nevertheless I could understand inner product at some level. Now that I have started Quantum Physics as well I have come across Hilbert space and bra-ket vectors.

My question is this: Are bra vectors one-forms an ket vectors vectors?

It would really help me if anyone could answer my question

Shounak

Professor Susskind:

I am greatly enjoying the physics courses that you teach at Stanford University. I am a layman with very little physics background.

In my late twenties (I am now 50) I read a science pocket book on electromagnetism written by Asimov. His style of writing took away the mathematical coldness and presented physical science in a totally new light.I then continued reading his collection of science books(although not the fiction ones).

I am now presently reading your book "the black hole war". I enjoy your style of writing as I did for Asimov.

I am new to this blog, so I would ask what are the parameter rules that I should follow when asking a question?

Thank you for all of your effort and time in exposing the scientific world to all of us out there.

Andre

Thank you so much for your lectures. They are addicting! Who know tensors and parallel transport would be so much fun.

Once again, thank you Professor Susskind.

Dear Prof Susskind,

I have been following your lectures on Special Relativity on Youtube and it prompted me to take a look at Einstein paper "On the Electrodynamics of moving bodies" I am having a little bit of trouble with the following part, and would would be grateful if you could help me out with the Calculus:

" 1/2 [ (0,0,0,t) + (0,0,0,t + x'/(c-v) + x'(c+v)]= [x',0,0,t + x/(c−v)

Hence, if x' be chosen infinitesimally small,

1/2 [1/(c−v) + 1/(c+v)]@T /@t= @T/@x' + 1/(c−v)@ T/@t "

I'm having trouble with how x'/(c-v) and x'/(c+v) become 1/(c-v) and 1/(c+v) when x' is chosen infinitesimally small.

Thanks.

The sun has been losing mass for billions of years, yet the earth keeps rotating around the sun. Why does not the earth spin away from the sun since the gravitational forces have diminished between it and the sun?

It is still not clear to me what gravity really is. We can define it mathematically, etc., but what is really pulling two objects in space together? It is certainly not magnetism or molecular, atomic, nuclear or electrostatic forces because at million miles away they amount to zero.

i am regular visitor of your site and you are writing very nice so keep posting university admission

Dear Susskind... I want to share with you new insgihts for string theory. This insightts can be a powerfull way to develop a a new approach for the standard model. I really need support to develop this in a form of a new theory. Do you like to work with me on this?

I am only Bachellor in Physics...

I work as a physics techer for my home university in Nicaragua....

On the other hand, If you can offer a teleconference for our university about relativity and string theory and other additonal thins, I can arrange it in order of a kind of exchange cooperation between standfor university and UNAN-MANAGUA in Nicaragua. UNAN-MANAUGA is my home university. What do you think?

George, check out article in latest infinite energy magazine, page 38, whats holding me down?? Another model of gravity. issue 91, may/june 2010.

Dr Leonard Susskind i am a new astrophysics student i am a 16 year old boy and i like to get some answers and to understand some explanations for some questions and ideas about physics i would like to ask you about:

1)i already know that light celerity is independent of sources velocity but why is that?

2)Dr Albert Einstein proved using his equations and the universal constant that the universe is a constant, later some scientist and hubble telescope proved that the universe is expanding and getting larger and larger in function of time and the great thinker was found wrong but i agree with Einstein even he was proved wrong because if we think this way we may take a smarter point of view: when the big bang process started and ended during this lap of time matter was already formed with a specific constant mass value that don't grow lager or don't loses any particle it's more like a system of particles in a closed box they interact they break into small particles but the total mass will never change so the big bang delivered a specific amount of matter and energy, then the universe has a limited mass and energy this why the universe is constant the expansion is not a mass expansion its density reduction in function of time, particles per meter decrease in function of particle speed and time

so Einstein is definitely right we are spreading in space not expanding there is a big difference am i right Dr Leonard ?

3) light is immaterial as we know than we should logically think that light is stopped by nothing else so why does light doesn't pass through obstacles(mass) why does is reflect on material object such as mirrors and walls then the fundamental composition of light has to be close to material object or else it would passes by everything. right ?

and we know that light deviates near a gravitating object and we all know that gravity force is affecting on material object so why does a black hole made of big amount of matter so hight gravity field that can deviate light from its initial trajectory so light must be material to make sense for everything right ?

hope i didn't bother you.

regards RAMEZ

HAVE A NICE DAY !!

I have 2 questions.

1. Just so i got it right, a tensor can be described as a property or operator that resides in EVERY point in a given coordinate system with n dimensions and the dimension of the tensor (and order) doesnt have to be connected to the coordinate system's dimension?

2. Reading Black Hole War I got stuck in a paradox. As matter can fall into Black Holes wont their mass become infinite as they approach or cross the Event Horizon. Wouldnt that make every black hole infinite in mass? I know im making some thought mistake here as i logical know that it isnt so but where?

Respected Professor Susskind,

I am at presently doing my PhD in String theory though am supposed to know many things but am unfortunately confused with many aspects of degree of freedom, and your lectures are very very help full in understanding many concepts. It will be of great help if you can help me with following questions.

1) Lets take one free particle in say 3 Dimension so as popular formula goes it will have three degree of freedom , but now ; let me go to understand since in position is independent of velocity, that means I can not only choose position but also velocity at my will and that will uniquely fix my configuration, so rather to me it appears there six degree of freedom rather than three, as in three for position and three for velocity components. From very simple way of looking x+y+z= 3 leaves with me only two choice of variable at my will and then third I do not have choice so I have two degree of freedom , similarly for free particle once I choose my three components of position and velocity it fixes my system uniquely so to me it appears six degree of freedom.

2) Lets take this degree of freedom calculation to General theory of relativity now am thoroughly confused at that stage, what I know is symmetric metric in 4 dimension to start will have 10 independent components but contracted Bianchi Identity will tell me that four equations of Einstein field equtions will be first order in time so they took them as constraint which reduced degree of freedom to six. Now they take harmoic coordiante which are used to remove those first order time to second order in time thus fixing cordinate noow am am confused what is what constraint and how many degree of freedom are free in four dimension.

Am sorry for so many questions but I did not had any really satisfactory answer so far from anyone.

Regards

Abhishek

Dear All:

Recently I found a series of physics lectures from Professor Leonard Susskind on youtube.

I would like to know is there any handouts of the course notes available?

Which text book is Professor Leonard Susskind mainly based on ?

This could help me a lot to catch up with the video lecture.

Thank s in advance.

Lee

chenyenlee@gmail.com

Dr. Susskind,

A thought is bothering me so much and I need an explanation for that so bad. I am sure you can answer that question.

What if we put an entangled particle into a black hole and observe the ther one. What is gona happen to the entanglement between both of them?

If entanglement stays, can we conclude the existance of Einstein Rosen Bridge?

what happen to the most fundamental particles when they hit singularity because according to the standard model they are not divisable?

Thank you

Dr. Susskind,

A thought is bothering me so much and I need an explanation for that so bad. I am sure you can answer that question.

What if we put an entangled particle into a black hole and observe the ther one. What is gona happen to the entanglement between both of them?

If entanglement stays, can we conclude the existance of Einstein Rosen Bridge?

what happen to the most fundamental particles when they hit singularity because according to the standard model they are not divisable?

Thank you

Hi folks,

I'm a retired graduate mechanical engineer living in Scotland.

I've just discovered the lectures and am enjoying the luxury of returning to some of the physics/math that was crammed in (without proper understanding) at university.

If you want a general scientific question to occupy an odd moment, here's one that's been bugging me for a long time:-

Many animals/insects/organisms seem to be born with the "experience" necessary to survive. eg a female cuckoo knows to lay her eggs in someone else's nest - obviously not something that she could have learned from either her biological or foster parents, since the biological parents are absent and the foster parents build nests.

Other more intricate examples abound, especially in the insect world.

What I want to know is this - if we constructed a nano-machine to assemble all the necessary elements, molecules etc required so as to accurately construct, say, a gladiator spider and it could be 'sparked' into life, would it know how to spin it's own particular type of web and use it the prescribed manner?

Can it really be that if you assemble a load of chemicals in a certain way, the assembly will 'wake up' with skills that have taken millions of years to evolve?

click:

http://nabucodonosor.bplaced.net

thank you !

Say there was a Universe with only one single black hole in it.

If this universe had no net gravitational energy, its universal law for gravitation would contain a positive constant (perhaps infinitesimally small), and the domain of the gravitating black hole would be a closed, and could therefore be defined over a distance interval between

aandc, ie. the Universe, where{a < b < c}, andbis defined where the force,{F=0}; then{ac=b^2}.But this could only be true if the distance

awas the event horizon of the black hole, and the black hole interior had no gravitational mass!A property similar to the conducting electrons on the surface of a conductor.

If it were true that perhaps through some confinement issues (since resistance to compression is a quantum mechanical effect that violates classical mechanics), black holes were essentially hollow, wouldn't this preclude the existence of the singularity, and would there be some consequence in General Relativity, since according to Einstein, "It is only the circumstance that we have no sufficient knowledge of the electromagnetic field of concentrated charges that compels us, provisionally, to leave undetermined in presenting the theory [GR], the true form of this tensor."?

The follow-up is this: Mlodinow, the other Leonard, recently claimed in a book, that only gravitating bodies in three dimensions could have stable orbits -which would rule out a theory of gravitation conservative in four dimensions (such as above, I think, since the derivative would be inversely proportional to x^3); but I don't believe him. Is this wives tale actually true for all possible theories of gravitation in 3+ dimensions?

About special theory of relativity simultaneity- Reference Robert Resnik

Q.1 Why don't we fix light sensitive clocks at endpoints of each reference frame and later observe whether two flashes are simultaneous or not.

Q.2 When moving observer notices one of the flashes earlier, doesn't he measure the velocity of light more than c?

I imagine General Relativity as Guassian surfaces, never points.

Given that context, if at a black hole event horizon the gravitational potential and kinetic energy of a falling particle are equated, then falling particles (or it's information), for it to reach the event horizon, would have to either be 1)completely transformed into electromagnetic information -and then never get out- or, 2)never fully reach the event horizon (since matter cannot travel at light speed without gaining mass and dilating it's own time): some proportion becoming almost stationary relative to an outside observer.

If this is correct, that matter in the process of falling in conjunction with more material, will continually form an increasingly massive (and dense?) shell of matter

just outsidethe event horizon, wouldn't this "stationary", increasingly massive shell be attracting to it matterjust insideof the event horizon: and not like Newton's hollow sphere theorem, but more like a parallel set of infinitely wide, gravitating, plates [Duhamel's Theorem]?I ask this question in the spirit of a point singularity at the center of a black hole that repulses me, but a shell type singularity, not so much. :)

On what basis the speed of light is fixed as the upper limit of all velocities? This may apper silly to you, but i want a suitable answer without ambiguity

I see that the last comment was dated April 21, 2008. Has everyone gone to sleep or gone over to twistor theory?

Professor susskind, first of all thank you so much for your generosity in making available these lectures. i have a couple of fairly basic questions about photons. Why is it impossible to have a rest frame for a photon? why are they compelled to move at speed of light? are the mass terms in diracs equations effectively a constraint on motion ?

finally, a relatvistic question, how does time work for a photon? wouldnt it always be everywhere from its perspective if it doesnt experience time?

Please help me and find my error in deduction:

The mathematical sum and difference rules for hyperbolic sine and cosine are (see http://en.wikipedia.org/wiki/Hyperbolic_function):

sinh(a+b) = sinh(a).cosh(b) + cosh(a).sinh(b)

sinh(a-b) = sinh(a).cosh(b) – cosh(a).sinh(b)

cosh(a+b) = cosh(a).cosh(b) + sinh(a).sinh(b)

cosh(a-b) = cosh(a).cosh(b) – sinh(a).sinh(b)

If any point (x,t) is situated on a hyperbola, then for all these points the next expressions will be true:

x = s.cosh(a); where a is the hyperbolic angle and s being the specific hyperbolic constant

t = s.sinh(a)

Any other point on this hyperbola (x',t'):

x'=s.cosh(b); where b is another hyperbolic angle of course than a

t' =s.sinh(b)

From all these information we thus can write:

x’ = s.(x/s).cosh(b) + s.(t/s).sinh(b) = x.cosh(b) + t.sinh(b)

t’ = s.(t/s).cosh(b) + s.(x/s).sinh(b)= t.cosh(b) + x.sinh(b)

THE BIG PROBLEM:

To my great frustration these are NOT the lorentztransformations as most of us know. The lorentztransformations are:

x’ = x.cosh(w) + t.sinh(w)

t’ = - t.cosh(w) + x.sinh(w) (mind the minus)

Can anyone explain the solution? Thank you in advance.

Alex Idzerda MD

Dear Prof Susskind,

I am a student of Pure Mathematics, however, I am in the middle of following your lectures on Classical Field Theory, which I find of great interest. Having completed the series of lectures on General Theory of relativity I learnt a lot.

In the latest few comments of visitors of this blog I was unable to find your replies therefore, I did not attempt to put my question up in the first go.

If you still follow to answer questions on this blog, please alert me with a reply. It will be much appreciated.

Regards,

I am currently studying QM and I had a doubt. You know that when you solve for the hydrogen model in QM, that because the hamiltonian, L^2 and angular mom in one direction are commutative you can get a complete set of identical eigen vectors for them. So say you do get an eigenvector for the hamiltonian with an eigenvalue E, doesn't the same eigenvector have one and only one eigenvalue each for the other two operators? so how come for the same eigenvector we have different values of l (eigenvalues)

Dear Prof. Susskind,

I am currently following your lecture course video on cosmology with great interest. I have the following question: according to classical Newton theorem the effect of a mass distribution on some outer point in space is the same as if all the mass is concentrated in gravity center, the energy potential depends only on the distance between that point and the Gravity Center. Now what about a rotating mass distribution when taking in count the Einstein gravity? does the energy potential of a test mass depend on the total angular momentum of the mass distribution?

Thank you

Prof Susskind:

I had a question on your SR/field theory lectures, where you get as a conserved quantity integral over d3x of pi(x)f(x), assuming phi -> phi + epsilon f(x) gives dL = 0. In trying to derive the conserved quantity, using the E-L equation for fields, I see that dL/dphi muliplied by epsilon f(x) gives 0, but on the other side of the e-l equation, you have terms d/dt of dL/phi dot, and if that is all, I see that you get the conserved quantity desired, but what of the other terms, d/dx of dL/phi x?

I seem to be missing the fact that these terms multipying f(x) and then integrating over d3x yields zero.

Sincerely, Adil Sanaulla

Dear Susskind,

Your lectures have been very helpful. Thank you for putting them online.

Please can you answer this question

Suppose there are 3 people a,b and c.

a is stationary, b travels with half the speed of light and c travels almost with the speed of light. And there is a mirror right in front of them at some distance x. If all three of them put on a beam of light at same time, which of the three would see the reflection first? According to special relativity, time would slow down for b and c. So all of them see the reflection at same time?Is it true? I just cannot imagine that.

Dr. Susskind - I know it is not exactly your area but I am interested in developing a Gauge Field Theory of Entropy. Field equations for entropy exist (ENTROPY, Greven, et al, 2003, especially Muller), but break down under conditions of high density. I am convinced that the Entropy field is scaler and Boltzman"s constant looks an awful lot like a coupling constant to me. Please comment or reply to my e-mail?

Dr. Susskind - I am interested in developing a Gauge Field Theory of Entropy. Field equations for entropy exist (ENTROPY, 2003, Greven, et al, especially Muller) but break down under conditioins of high density. I am convinced that the Entropy field is scaler and Boltzman's constant looks an awful lot like a coupling constant to me. Please comment and/or reply by e-mail. Has anyone else been doing work in this area?

I did lot of research and couldn't find the answer to following question, "Is it possible that humans are at least 11 dimentional creatures?", such that first three are spatial, forth being time and last seven as described in String theory.

Dear Professor,

We are the same age.

I saw a programme last night on TV about black holes and the battle you won against Prof. S Hawkins.

You said in the program and demonstrated the red dye diffusing in the water becoming homogenous. But stating the order it all came about was still there.

What do you think as to a canera that takes a picture but out of focus?

It seems to me that all the information is there on the film and there ought to be a way to correct the photons order?

Perhaps your mind can do this? Mine can't but it would be amazing and a scientific breakthrough don't you think?

Sincerely Dennis.

I was looking at the cosmology course on youtube course 4. Something is strange or perhaps i miss something. The vacuum pressure is P = -ro (w=-1) where ro is the vacuum energy density. The energy is always positive so as you said in the course the negative pressure can be associated with a tension. This doesn't mean that vacuum tendency is to contract not to expand? On the other hand we are all assuming that a(t) [expansion function] for vacuum is an exponential which goes to infinite when time elapses. How can be possible that negative pressure can cause expansion?

In the entanglements lecture series, towards the end, when Leonard spoke about EPR, I found it quite unusual his claim that "there is no violation of locality ... I don't know what everyone worries about it" etc. First this is incredibly dismissive and irresponsible. It is of my opinion, and many other Physicists, that the singlet -> 2 electron system if understood, represents a situation in which the concept and logical reasoning forming locality (and causality) are ABSOLUTELY infringed upon. Coming from Leonard, the comment above was very suprising.

This "felony" has probably been re-explained correctly somewhere? I hope so. :) dr Joe haskian.

Hi, i'm from Rome Italy, mechanic engineer.

I'm following your lessons on youtube.

I'm at the photon / elevator example which has made a question aggressively jump in my mind.

The mass of the photon.

I read on WIKIPEDIA that a photon as a zero rest mass.

But they are pretty speedy so how one can say what the mass of the photon is?

Is it measurable the non-rest mass?

I'm sorry for possible multiple english errors and / or ingenuity of the question.

Thanks.

Dear Professor Susskind,

I am interesting in the invariant forms for special relativity, and clearly invariance holds are per the Lorentz transformation. But a question that I often wonder about is, although relativity impies isotropy, it is not required to satisfy invariance.

What are your thoughts on that?

Regards

Estelle

After checking the blog responses from Dr. Susskind, I think it is safe to say that Dr. Susskind is no longer responding to this blog. This is why I removed my previous posts.

I'm currently watching the Statistical Mechanics lectures and would like to get a copy of Professor's Susskind's lecture notes. How do I do this?

We all have been taught from HS physics that the photon is the only massless particle at rest and that can travel at the speed of light.My question is :Does it exist other particles,but this time with rest mass that can travel at the speed of light? And what would happen to physics in case scientists bump into such particles?

In response to Ahdaf....

Accelerating a non-zero rest mass particle to the speeed of light would require an infinite amount of energy and therefore cannot be done.

hello my name is benny roose,i'm a highschool student in belgium and i've been wondering and searching for a proof why we can't make a linear superposition of the tensorproduct of position eigenstates and momentum eigenstates. could someone give me a link to the proof or the proof it self. thanks in andvance.

Does blogspot not support LaTeX ?

It would be a whole lot easier!

Suppose a spaceship is falling into a black hole. According to General Theory of Relativity, the closer the spaceship gets to the event horizon, the slower its clock will be ticking relative to a distant observer. We also know that black holes emit particles. And the lighter a black hole is, the more intense the radiation will be. Since the clock is ticking slower for the spaceship, than for a distant observer (one second on the spaceship will be equal to, for instance, one year for the distant observer), the radiation intensity will grow faster for the spaceship. Doesn’t this mean that the spaceship will never reach the event horizon because the black hole will completely evaporate by that time?

Hi, I am a 14 year old teenager and i finished your book entitled,"THE BLACK HOLE WAR".I learned a lot about the physics that you used to prove the theory that you made about information coming out of a black hole but i'm still unfamiliar about the laws and basics of quantum mechanics. Can you recommend me a book about quantum mechanics?

This is a lower level question than the ones I see here, but I really am a beginner layman...

In your book "The black hole war", at the end of chapter 4, it is stated that the probability of an event happening is given by squaring the sum of the amplitude probabilities (Feynman and Dirac) and this square is always positive. A few lines before, it is written that than amplitude probabilities can be positive, negative and also complex numbers. Now, if we sum different amplitude probabilities,we may end up with a complex result, and the square of a complex number is a negative number: so, unless there is something preventing the sum from being a complex number, we may end up with a negative overall probability. Since this is nonsense, what am I missing?

Thanks

Robert, Milan, Italy

Dr Susskind,

I have tried to follow, at least at a qualitative level, the development of String Theory and I believe that I understand that the theory describes a universe in which all particles are manifestations of strings, terminated on branes, in a compactified multidimensional space. So far so good, but when the question "what are the strings/branes made of" is posed the answer appears to be "they are fundamental". This appears to be very similar to the situation before evolution of the standard model where particles such as electrons and nucleons were regarded as fundamental and begs the question "could there be a further level of structure below string theory?"

I have read your book "The Black Hole Wars"and I think that I understand from that and other reading that the holographic principle states that all the information and hence all the complexity in a system can be represented by a hologram on an event horizon surrounding the system. My query is, does the holographic principle therefore put a physical constraint on the information content and hence complexity and therefore indicate that a fundamental theory exists, which may or may not be string theory?

(@ PLEASE READ @)Dear Mr.Susskind

I have a briliant idea !!!

i always saw the videos about the bosons and the fundemental forces but i didnt knew how the boson is pulling the neotron\proton

the i got this fantastic idea !:

everything is a string\membrane right?

so the proton is a membrane and it reaples, if the reaples are really violent the brane could(in theory) twist on it self ! and can(in theory) break in to two !! brane 1 is the proton and brane 2 is the new one, brane 2 inherits all of the vibrations propoties of its father but less vibrations can fit on it because its smaller ! so it has differrent propoties ! well brane 2 can fly in any direction untill it hits other brane(brane 3)

when it hits brane 3 they lock on together and combine, the vibrations of brane 2 echos in brane 3 and it gets stable(the vibration is an averege of the two previous)

that way it gets some of the propoties of brane 2, now heres the cool part ! :

all protons "shoot" those membranes so they lose parts in every directions but if there is another proton near the other proton returns those lost membranes

so they are sort of get built in the direction of the other proton !! they dont move ! they are getting built toward each other !!

now membranes that doesnt vibrate in a violent way will not "emit" branes ! and membranes that vibrate randomly will emit branes with diffrent propoties so one membrane could emit many types of branes(bosons) the proton emits strong bosons an magnetic bosons so it must be random in some way !

@matantsuberi: what do you mean 'briliant' ???

genius !! (a smart idea)

sir

This is ram pandey from india

i am doing my graduation in electronics and communication but i am interested in studying cosmology and i want to persue some research in the same.i have acquired quite a knowledge about the same and i am looking for a topic to work on.

so can you please help me with topic selection that has scopes in future

of course ! i will be glad to help you ! you want agenral overview or a specific topic ?

(i am matan tsuberi)

9millimeters X 9millimeters = 81 millimetres

the above expressed in meters is:

.009meters X .009meters = .000081 meters = 0.081 millimetres

the answer is wrong when millimetres is expressed in meters multiplied as meters and the product is then expressed in millimeters..

then how can 10 to the power of -35 multiplied by 10 to the power of -35 equal 10 to the power of -70

(page 154 of the black hole war).

unless you have a specific unit to express muliti-nano lengths how can you square or multipy using a much larger unit of meaurememt where that small unit has to be expressed in decimals....?

What i mean to say is when you express anything in decimals of a larger unit it is ok but when you square the same you will be wrong..

9milimeters X 9milimeters = 81 millimetres

the above expressed in meters is:

.009meters X .009meters = .000081 meters = 0.081 millimetres

the answer is wrong when millimetres is expressed in meters multiplied as meters and the product is then expressed in millimeters..

then how can 10 to the power of -35 multiplied by 10 to the power of -35 equal 10 to the power of -70

(page 154 of the black hole war).

unless you have a specific unit to express muliti-nano lengths how can you square or multipy using a much larger unit of meaurememt where that small unit has to be expressed in decimals....?

What i mean to say is when you express anything in decimals of a larger unit it is ok but when you square the same you will be wrong..

9milimeters X 9milimeters = 81 millimetres

the above expressed in meters is:

.009meters X .009meters = .000081 meters = 0.081 millimetres

the answer is wrong when millimetres is expressed in meters multiplied as meters and the product is then expressed in millimeters..

then how can 10 to the power of -35 multiplied by 10 to the power of -35 equal 10 to the power of -70

(page 154 of the black hole war).

unless you have a specific unit to express muliti-nano lengths how can you square or multipy using a much larger unit of meaurememt where that small unit has to be expressed in decimals....?

What i mean to say is when you express anything in decimals of a larger unit it is ok but when you square the same you will be wrong..

how can anything less than three dimensions exist.. i mean how can you see only length if the object does not even have a planks length of breadth..? and in three dimensions how can you see an object that has length and breadth but not even a planks length of thickness. Thus a rectangular piece of paper cannot exist unless it has some thickness even if it is a miniscule amount of the plank's length itself!!

dear sir

I used escaped velocity on the surface of a black hole to be equal to velocity of light and considering a blackhole to be a sphere i reached a conclusion that its density is inversely proportional to square of its mass as, d=(3c^6)/(32piG^3M^2)

d=density of black hole

C^6=sixth power of the velocity of light

pi=22/7

M^2=square of the mass of black hole

G^3=third power of gravitational constant

if its the right calculation then why is it inversely proportional to square of mass

Yours

Ashish Bastola

dear sir

I used escaped velocity on the surface of a black hole to be equal to velocity of light and considering a blackhole to be a sphere i reached a conclusion that its density is inversely proportional to square of its mass as, d=(3c^6)/(32piG^3M^2)

d=density of black hole

C^6=sixth power of the velocity of light

pi=22/7

M^2=square of the mass of black hole

G^3=third power of gravitational constant

if its the right calculation then why is it inversely proportional to square of mass

Yours

Ashish Bastola

Any transformation between two observers is a space-time dialogue between two entities A and B about a third entity C. In the 'Galileo Transformation', the third entity C is understood, does not appear in the notation. But the 'Lorentz Transformation' completely ignores the entity C, and this is why the twin paradox.

I would like to introduce some new transformations that preserve the local velocity of light. Also resolve the twin paradox.

Relational Transformation: http://vixra.org/abs/0909.0022

Thank you for sharing and satisfying this curious person and many others.

Very kind you are.

kaitrees

Dear Professor,

I would like to ask that how would you co-relate the reflux action of human body in context to special relativity.

Dear Professor,

Although the acceleration of the expansion of the universe has been empirical demonstrated, it still puzzles me that the only explanation would be an unknown force called dark energy pushing things outward.

Has the idea ever been explored that instead of a force PUSHING from the inside something is PULLING from the outside? That is where the idea of multiverses I discovered in your book “The cosmic landscape” comes into play. A certain distribution of masses due to these multiverses would exert a force similar to a dark energy from the inside.

How to prove this theory could then maybe be shown indirectly by mapping the acceleration of the cosmic expansion in all directions. A formidable task, not comparable to measuring the cosmic background radiation and probably not possible with the actual method. If there is something behind the horizon of our universe then it will most probably be not evenly distributed in the near field a lead to a uneven distribution of the acceleration in different directions and clearly be different from the cosmic background radiation fluctuations.

Could you tell me whether this idea has already been explored and if any articles have appeared?

Thank you for your time. I very much appreciate the opportunity to see you live in the video courses.

Kind regards, Peter Reynaert - Belgium

Hi, I got one question that boggles my mind...

I watch a lot of black holes shows..

I wonder does the event horizon covers one axis only?

I mean what happen if we were standing right above the black hole?

Would be be pulled inside or only if we are on the horizontal direction then we will be pulled inside?

Dr Leonard, I have been reading up on String theory and I am glad that it has the potential resolve and explain lot more physical reality. But what I still don't get is the supposed oscillations of string. How are these strings to be imagined? Are they supposed to be curvy loops? What is the difference between vibration of string and oscillation? Another concept I never understood is the concept of energy. We keep saying this and that releases energy. But that does not make any sense unless we mean that energy itself is further explained in some terms in the fundatmental strings in motion. Does string theory explain the notion of energy itself?

Dear Professor Susskind,

I recently started a discussion in an electronics forum about conduction current in a conductor versus displacement current in a capacitor.

Here is a quote of my comment:-

“I suspect that when the physicists derive the "theory of everything", some of these concepts & terms will need to be revised.

For example, if string theory proves to be correct, then current may be shown to be a flow of strings.

I say this because the concept of current flow being the flow of charge carriers does not cover the concept of displacement current.

I believe this concept is derived from Maxwell's equations which, as I understand it, show that there is a displacement current through the dielectric of a capacitor even though there is no flow of charge carriers inside the dielectric: note that the dielectric could be a vacuum.

This raises the question in my mind - why do we need a conductor to carry current?

Obviously the charge carriers in the conductor play a role of some kind.”

This started a storm of protest. Several people argued that Displacement Current was a ruse by Maxwell to cover up a weakness in his equations. They insisted that a current IS a movement of charge carriers. There were 2 or 3 people who supported my argument – that Displacement current is real - but they did not comment on the “string theory” issue.

I would like to hear your thoughts on this issue.

A question re rest mass.

If I have a 1 kg lump of uranium, it has a rest mass of 1 kg.

But if I take it in my space craft at a significant speed, then I assume it still has a "rest mass" of 1 kg in my reference frame.

However, an Earth bound observer will deduce that it has a much greater mass.

My conclusion is that I would be able to make a much bigger explosion using the Uranium in my space craft than I would if I used the same lump on Earth.

Putting it in other words, "rest mass" is a relative term. There is no absolute "rest mass" as there is for temperature, ie. 0 deg K.

Is this true?

Velocity effects the flux fields, generating higher frequency affectation of the reult.

Velocity excites the flux fields that permeate the voids around the strings.

This is my first time in a blog (I successively posted 2 yesterday - after some messing around).

So I'm not familiar with blogging.

Could someone please explain how I reply to someone's blog.

I tried to reply to the one by Alex Idzerda but I found the instructions were in a foreign language so I'm not sure if it was entered into the system

I can't see it at the end of the blogs. Does it take some time to appear?

May I suggest that immortality could be explained when we discover our relationship with our personal string - or what may be described as our spirit.

As a theologist looking at the science I can't help but feel a very real connection between the two and I have no doubt that science can combine them.

I beleive that god is not yet a mature being and was born with us at the big bang,and together we are evolving toward a true golden age.

Einstein and Jeus have convinced me that death has no meaning and my string and I could have a forever thing going...

Dear Sir

May I suggest that immortality is very real and may be explained when we discover our relationship with our personal string - or what can be described as our spirit.

As a theologist looking at the science I can't help but feel a very real connection between the two (us and string)and I have no doubt that science can combine them.

I believe that god is not yet a complete being - was born at the big bang and is evolving as we gain more knowlege and mould it with our morality.

Einstein, Jesus and an incredibly full life have convinced me that death has no meaning. No matter what colour shape or form my string thing takes, I am sure it has the ability to live forever.

And 'I' intend to savour every millenium of it!

Best regards

Aussie Crackpot.

I am currently reading your book - The black hole war- and i went through the part where you said that the rubber sheet and bowling bowl model was all wrong.But , the space is extremely larger than any celestial object.So,even if you consider a gravity free space the sheet(space) would be far bigger and the body with a huge mass would create a warp.Am I right?

I am currently reading your book-The black hole war-in which you said that the rubber sheet-bowling bowl model was all wrong.But,actually the space is extremely larger than any celestial body.So even if you consider a gravity free area the body won't fly off and would create a warp in the "sheet"(space).Is it possible?

I am currently reading your book-The black hole war-in which you said that the rubber sheet-bowling bowl model was all wrong.But,actually the space is extremely larger than any celestial body.So even if you consider a gravity free area the body won't fly off and would create a warp in the "sheet"(space).Is it right?

I am currently reading your book-The black hole war-in which you said that the rubber sheet-bowling bowl model was all wrong.But,actually the space is extremely larger than any celestial body.So even if you consider a gravity free area the body won't fly off and would create a warp in the "sheet"(space).Is it right?

Is the following nearly correct:

the Mexican Hat potential was found to be sufficiently close to matching experiment as to be useful.

If so, then tweaking the parameters of the polynomial describing this potential to most closely match experiment seems to make sense.

Or is there some inherent reason why that should be the "obvious" potential to use.

I don't yet understand where this potential comes from, but assuming it, I see the Higgs mechanism then makes sense.

Professor Susskind,

I've developed what I believe is a new and interesting form of the Lorentz transformation that directly elucidates the role of the 4 velocity in the transformation. But I don't know whether I'm reinventing the wheel, or whether this is truly something new. I'm hoping you would be willing to look it over and tell me your opinion. (I don't have direct access to the literature because I'm retired). I would like to send you a WORD writeup. Please let me know, and, if so, how I should address the document.

Chet Miller

Dear Sir.

My question is that,

As we know that (e.g. sun and the earth), it takes 8 min approx for light to reach earth. Suppose the sun goes dark instantly that means we'll know about this incident after that 8 mins, thats very clear. Now the problem is that "If the sun disappears (vanishes totally) from this universe instantly" means there is no more sun now, then we know that it will take 8 minutes you visually see this scene but my question is, after how much time (counted from the disappearing event of the sun), the earth will leave its orbit? and in what direction it will go? if it leaves the orbit at the same instant than gravitational effect should have more velocity than light.

Shahzeb Kamal

Punjab University, Pakistan

Dr. Susskind:

I just watched the first video in the Quantum lecture series. I was greatly impressed by the clarity with which you explained the basic approach to physics and clarified some of the mechanisms I'd read about but failed to thoroughly comprehend.

I graduated from college 40 years ago. I wish I'd had professors who were as able to explain complex things as well as you seem to have done in this lecture series.

I am interested in finding out how things work, how things are put together: I am sure your lectures will be valuable in this inquiry.

Thanks for your approach. I appreciate it.

Sincerely,

RonZ

Hello professor,

I followed your lectures on Special theory of relativity.

Here's my doubt:

Although the "Twin-paradox" explains quite clearly that there will occur an actual difference in ages of the two twins who follow different curves in space time, i don't quite understand whether "Time-dilation" and "Length-contraction" are only the effects of frame of reference like "simultaneity", which is an illusion bound to our frame of reference, or they happen for real?

More precisely, if i watch an aircraft whizz past me at near the speed of light, will it "appear" to me as if the aircraft is shrinking in length, or would it "actually" shrink in length??

Thank you sir.

@Shahzeb:

yes, the earth will follow its orbit for 8 mins after Sun disappears.

Gravity travels in the form of gravitational waves that travel exactly at the speed of light.

So, as soon as u stop seeing the Sun, the earth will leave its orbit, following a tangential path at that instant..

ir,

In lecture 3 on special relativity you said that --

"For a light moving in different kinds of material, the time it takes for the light to travel from one point to another is the shortest possible time."

But I have heard about cerenkov radiation whose definition is " Electromagnetic radiation which is emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium."

so doesn't this particle travel the distance between two points in the shortest time in that medium?

Dear Professor Susskind,

obviously eleven year old girls understand more of physics than me, so my question might seem a little dumb.

I recently saw a television programm about black holes and the holographic principle.

What I want to know is if I might imagine this holographic effect like the 2-D grid laid on the dura mater to locate the 3-D location of an epileptic event taking place in the brain, just that the information is somehow stored there??

I have a question about the theory of relativity. I was reading a book by Brian Greene, and he said objects move through the 4 dimensions of space-time at the speed of light. Does this entail that in a parallel world where time runs 10 times as fast, time runs 10 times as fast?

Dear all,

Leaving in Geneva, near the LHC, I've just discovered the online course, unless it was a blasphemy I'd said the communication of this knowledge is a miracle...

Besides, I need a guidance - I just 'graduated' from Classical Mechanics and arrived to Quantum Mechanics Lecture 3. As I noted I miss to many concepts, I wondered what is the best way to move on with the courses, subject-wise I mean. Please note that my end goal is to better understand Quantum Field Theory and current alternatives to the Standard Model.

Any typ is highly welcome;)

Yariv

Blackholes!!!!

I have a thought which I would like your views on, suppose the blackhole is a junction for two massive hawkings particals which could also be suggested as the meeting point of two opposite or very similar/exact realities/universes.

our perception of the passage of time can or should be scaled from what our perception is to smaller and larger objects like dog years, to try and clarify this thinking say you are scaled so that the size of a blackhole to you would just be smaller than the size of a hawkings partical then you may percieve the two particals/universes cancel each other out at the rate we at this scale see the same event take place with two hawkings particals from our natural size

therefor it could be suggested we reside within a hawkings partical which is coliding with an other one both canceling each other out at least to a point tho this might not be the effect of two such particals they may in fact combine to creat something we as yet might not have considered be it a new universe outwith ours and our sister on which may be converging on a black hole, sorry if this sounds a little confusing as I see this clearly but voicing my thoughts and ideas cause me some confusion ha ha

Thank you for the many lectures on physics. Hard but fun for an old

retired engineer.

I have wondered for some time about the time axis in relativity. I

have heard other places that the conversion factor or translation

factor of time axis to any space axis is the speed of light, 186,000

miles equals 1 second. Thus the units are the same in all space time

axis. If this is so, then it seems to follow that we are moving along

the time axis at 1 second per second (I E time passes at 1s/s).

So how can we (every THING), as real objects with mass, move at the

speed of light along the time axis but not along the space axis (where

only light can do this)? Maybe you can get a Grad student to help an

old guy learn a new trick (of visualizing).

Again, thank you very much for the lectures. I am enjoying trying to

understand all that I don't understand as much as the little that I do

understand. ;) Thanks, Gary

ITS VERY INTERESTING WHAT GARY HAS BROUGHT UP.

IT SEEMS MR SUSSKIND HAS GIVEN UP ON THIS BLOG AS HE NO LONGER SEEMS TO ATTEND IT.

IT HAS BEEN A PLEASURE FOR YOUNG AND OLD INTRIGUED SCIENCE DISCIPLES LIKE US TO LEARN N UNDERSTAND THE CONCEPTS OF MODERN PHYSICS..

Sir..

I want to know whether there are lectures available for electromagnetism and its deep connection with the special relativity from you? I am really searching these lectures from long.

Please help me.

sir

I want to know whether there are lectures available on Electromagnetism and its deep relation with special relativity by you? I am really searching these lectures from long.

so need you help..

Vishal: Professor Lewin of MIT has some basic lectures on Electromagnetism on line. Professor Susskind deals with the Relativistic Invariant form of Maxwell's equations in lectures 5 & 6 of the series on "Special Relativity" which is actually labelled "Quantum Entanglements Part 3. I suggest starting at the beginning, but this link should get you to Lecture 6

http://www.youtube.com/watch?v=YTGvPL2qbFI&feature=relmfu

Gary,

I'll take a shot at answering your question. I think the problem is your use of the verb "move" and noun "motion" in two different ways. The usual meaning of 'motion' is a change in x over time. This is the motion that is limited to the speed of light (c). In most of his lectures, Professor Susskind uses units so that c=1. I think this is what you refer to. However a change in t with respect to t is not "motion" in the normal sense. t (time) is different from x, y, z (spatial components). So, dx/dt is limited to values less than 1, but dt/dt = 1 (always and forever).

Stephen: How could you measure time that 'runs 10 times as fast' as time in our Universe? The clocks in that Universe would all show that 1 second takes one second to elapse. The unit of time (e.g. second) is quite arbitrary, but once it is set, a second is a second is a second (for all stationary observers).

One thing puzzles me about modern cosmology. When I went to school, energy was defined as the ability to do work, but now it is supposed to be the stuff which emanated from the big bang.

So my question is, given the above definition, how could there be any energy before there was any hard stuff for forces to push around?

Leslie,

I have the ability (potential) to lift 50 pounds. Does the fact that there are no 50 pound weights around negate this potential? Likewise, energy can exists without anything to push around. An electric potential field exists around a charged particle, in the absence of any other charges to 'work' on.

The definition doesn't speak of energy as being something sitting there, just waiting for some mass to turn up so that it can do some work on it.

It defines energy in terms of work, and work is in its turn defined in terms of mass.

I suppose what I am saying is that, if energy is something which can exist even in the absence of mass, then we need a new definition of energy.

Leslie, I quote from your original post: "When I went to school, energy was defined as the ability to do work". This 'ability' is potential (energy). There can be "ability" without actually doing anything. Potential energy is often energy of position. And the potential field 'just sits there'. It doesn't have to do anything (act on a mass) to be energy. It can act on a mass, which would be the actual doing of the work. This would then represent transformation of the potential energy into kinetic energy. There is no conflict between the two definitions.

@Leslie..

to add to ShakeSpear, i'd say that the two definitions are in perfect harmony like Shake said, its just that, at school level the scope of resolution has to be kept within the grasping ranges of young minds, so everything u've studied in there was simpler definitions everywhere..

hope ur queries have resolved!

1.) Energy is defined as the capacity to do work.

2.) Work is defined in terms of mass.

3.) In the very early universe there was no mass.

4.) Therefore in the early universe the definition was meaningless.

5.) This something called energy, which was without a meaningful definition, was nevertheless created.

And how would you quantify this "stuff"? You couldn't do it it terms of gravitational potential, or the potential energy stored in a battery.

Leslie, #3) I don't agree there was no mass. There may have been no particles of matter in the early Universe, but there was plenty of mass. Mass = Energy.

sir,

is there enough reliable data to suggest that the speed of light is indeed slowing down with time?

-ayushman

Respected Sir,

My name is Vaibhav from Mumbai (India)

I am Working in a software firm as a software engineer, but i have very much interest in Physics. Daily i used to go through your lectures that are available on the Internet. Thanks for your efforts sir, due to these efforts person like me can able understand the laws of physics & believe me sir i get inspiration from you.I wanted to be Astro-physicist. Currently i am learning from your lectures only.

Sir when i am free i used to thinks about physics only.

Recently i was thinking about the Speed of light & got some doubts which i wanted to ask you. Sir as we know that Speed of light is the Cosmic Speed limit that we can not achieve till now.

but Sir We can control the Speed of light by passing it through different medium say glass, Water etc. in these medium light travels at different velocity that it travels in air & vacume.

So Is there any medium that we can build so that speed of light can boost up i.e.it could cross Cosmic Speed limit when traveling trough that medium.

I am not aware of any of such medium but can it be possible ?

sir please tell me i will wait for your reply.

my email ID is vaibhav.08k@gmail.com

Vaibhav,

An interesting question: can a material exist in which the speed of light is greater than c. As an amateur physicist, I would have to answer "no" to your question. First, if such a material existed, then information could be sent from one place to another faster than the speed of light (in a vacuum). I believe there would be logical contradictions that then arise in the Theory of Relativity.

Second, a simplistic explanation of why light slows down in a physical medium is that there are (quantum) interactions between the light and the material. Any such interaction takes time (creates a delay) in the transmission of the signal, so the speed will always be less than c.

And I could be wrong.

I am no scholar, but I gather information in a very different way, I have been lead to the fact that the particle Anyon has something to do with your work being that it is in a 2 dimensional state - I feel the connection between it and our reality in a 3 dimensional state is in fact the process we go through from death to birth. It is the place where all information is retained and also where we go when we leave our bodies. Like the fringe of a black hole and the reality surrounding a black hole.

Hello,

I have a general question about gravity. From the few books that I have read, there seems to be general agreement in the existance of a graviton, but apparently it also seems that the graviton hasn't actually been discovered yet. It got me thinking, are there any other theories for gravity being pursued in the physics community (i.e. ones not based on the concept of a graviton)?

As an example, I've always wondered if gravity is a push concept rather than a pull concept. A rectangular sponge is a good example of what I'm thinking about. If you take a rectangular sponge and somehow place a ball in the middle of it, the surrounding sponge would push on the ball's surface. I wonder if spacetime behaves in a similar way with objects like planets, where spacetime is pushed out around an object and that creates a sort of downward pressure around the object. In essence, I wonder if there is really no graviton at all.

Thanks!

Neal

- Philosophy of ‘ Vacuum.’ ( Part 1.)

1.

In beginning was Vacuum an Infinite / Eternal continuum.

2.

Vacuum is not Empty space.

‘ Virtual particles’, ‘ dark matter’ and ‘zoo of elementary particles’

exist in the Vacuum.

3.

Now (!) the physicists think (!) that the Universe as whole has

temperature: T= 2,7K . The parameter T=2,7K is not constant.

It is temporal and goes down. In the future it will come to T= 0K.

4.

The simplest question: Which geometrical form can have

the ‘ virtual particles’, ‘ the particles of dark matter’ ,

the ‘ zoo of elementary particles’ in reference frame

T= 2,7K - –--> T= 0K ?

The answer is: ‘ They must be flat particles.’

Why?

Because according to Charle’s law and the consequence of the

third law of thermodynamics as the thermodynamic temperature

of a system approaches absolute zero the volume of particles

approaches zero too. It means the particles must have flat forms.

They must have geometrical form of a circle: pi= c /d =3,14 . . . . .

====.

Best wishes.

Israel Sadovnik. Socratus.

========================…

- Philosophy of ‘ Vacuum.’ ( Part 1.)

1.

In beginning was Vacuum an Infinite / Eternal continuum.

2.

Vacuum is not Empty space.

‘ Virtual particles’, ‘ dark matter’ and ‘zoo of elementary particles’

exist in the Vacuum.

3.

Now (!) the physicists think (!) that the Universe as whole has

temperature: T= 2,7K . The parameter T=2,7K is not constant.

It is temporal and goes down. In the future it will come to T= 0K.

4.

The simplest question: Which geometrical form can have

the ‘ virtual particles’, ‘ the particles of dark matter’ ,

the ‘ zoo of elementary particles’ in reference frame

T= 2,7K - –--> T= 0K ?

The answer is: ‘ They must be flat particles.’

Why?

Because according to Charle’s law and the consequence of the

third law of thermodynamics as the thermodynamic temperature

of a system approaches absolute zero the volume of particles

approaches zero too. It means the particles must have flat forms.

They must have geometrical form of a circle: pi= c /d =3,14 . . . . .

====.

Best wishes.

Israel Sadovnik. Socratus.

========================…

It is actually true that the gravity is actually a push concept rather than pull. Newton says gravity pulls as you come near the proximity of mass. But Einstein says because of matter the space-time is curved ans as a result the space time pushes you towards that matter.

Dear Mr. Susskind,

I'm at lecture 6 of quantum mecanics and my question is about the singlet configuration and the violation of Bell's inequality: you say that when 2 electrons come close enough to interact their spins become opposite. How come we can measure pairs with one up on z and the second up at 45 degres if they are supposed to be all in opposite direction? Thanks

Germain,

It is in the nature of Quantized spin, that measuring spin in ANY direction (along x, or y, or z or at 45 degree angle to z) can only result in one of two answers, UP or DOWN. That is UP or DOWN along the direction in which you measure.

Thanks Sake Spear for answering!

I realize that instead of bothering a lot of people with my "may-be basic questions" i shouldn't ask for anyone to be my mentor so we could chat or E-mail on quantum physics?

Anyone interested!

Dear Dr. Susskind,

In your book "The Black Hole War" you repeatedly refer to the hot temperature just above a black hole's horizon (as seen from the outside). But this does not grok with me, since time is supposed to slow to a near standstill in this high g region, and how can you have a high temperature with time moving extremely slowly?

Thanks you,(and thanks for the fine book),

John A. Gowan

Respected Sir,

My name is Vaibhav Khamgaonkar from India,i have done Engineering in Electronics & Telecommunication & Currenty working in Software firm but I have very much interest in Physics. i used to watch your lectures every day. Thanks a lot sir for such a wonderfull lectures due to which person like me who desprerately wants to understand our universe, its laws etc can understand with it.

before that it was hard for me to realise how the laws of nature works.

Sir i want to be a researcher & i think these lectures can help me doing that.

Sir i have a doubt in mind that i wanted to ask you. We know the cosmic speed limit (light speed) & which can not be exceeded but we can reduce it by sending it throught different mediums (glass, water etc). My query if we can reduced the speed of light by passing it trought certain mediums then it should also possible that we can increase the speed of light for some other mediums?

please suggest Is it possible?

my email id is vaibhav.08k@gmail.com

Dr. Susskind,

I just wanted to express my sincerest gratitude for all you've contributed to the scientific community and the world at large, and on a more personal note the genius that you've made accessible to a curious student such as myself. You're a great teacher and I'm a huge fan!

I will keep reading and watching your material as fast as you can produce it! Your books are worth every penny. Thank you.

I just have a question about simultaneity in special relativity, which says that which events are simultaneous is observer dependent; that one cannot synchronise 2 clocks and have every observer agreeing on it. I shall point out a mechanism by which synchronisation can be done absolutely. Please point out the flaw.

Gedanken: Two clocks which start ticking upon being pressed a button on them. A symmetric inverted T bar, and 2 clocks kept symmetrically at either ends of the inverted T-bar. By applying force at the single point at the top-end of the inverted T-bar the horizontal-arm of the inverted T-bar comes down and presses the buttons on the 2 clocks, thus synchronising them. I dont see why any arbitrary inertial observer would disagree.

Zero, Imagine your two clocks at two light years apart. Your 't-bar' must be two light years long. When you apply your force to the center of the t-bar (assuming you can accurately locate the center), that signal is not transmitted instantaneously, but travels as an energy wave thru the material. It takes at least one year to reach each of the clocks to start them moving. You have no way of knowing that the signals took exactly the same time to reach the two clocks. The material may not be uniform, there may be differing gravitational influences on the material along the two arms, etc. You have no guarantee that the two signals travel at the same speed, therefore the synchronization fails.

I think you get a similar problem just sending two light signals from the 'center' between the two clocks. Even though the light travels at a constant speed, determining the 'center' is problematic.

Dear ShakeSpear, are you appealing to non-idealness of the material or construction of the inverted T-bar? I thought such idealisation was allowed in thought experiments. However, the travel speed of the "energy-wave" which is the signal for the horizontal arm to descend might well be the answer to my question, I am not sure though. Thank you very much.

Zero, you are correct, I relied on the non-idealness of the material. I'm not sure whether this is 'allowed' in a gedanken or not.

Perhaps the real issue is finding the center between two points. Because you could more easily send a light beam to each clock as the trigger mechanism. If you knew you were equidistant between them, this would have the same effect as your T-bar.

What are your views regarding special relativity after the discovery of the neutrino's capabilities to exceed the speed of light. What would this mean in terms of physics?

basically i am a school teacher and regular reader of your blog , you are sharing valuable information which are really helpful for my students., keep updating..

top engineering universities in pakistan

if the beam of neutrino is really faster than light. relativity will be wrong then will quantum mechanics be affected

Professor Susskind, recently an investigation group has published that neutrinos travel faster than photons. If that were true, could you please explain the subsequent implications this discovery would have for theoretical physics?

Hello Professor Susskind,

I'm an spinsh engineer, and an apassionate on physics.

I have read several times your book "The blakc holes war" and enjoy everytime.

Just thank you for vour dedication and passion on physics. Humanity will go on if we continuate to improve our knowledge on natural laws and how we can take profits of them.

Thank you very much.

(excuse me if the gramatic or ortography is not correct)

Oops, sorry, my question (1) is answered on page 7 of your Hawking book.

Thanks for your work. I'm just starting your book about Hawking. I have a couple of questions.

1) Is general relativity a field theory? I have the impression that maybe it isn't, and that this is one reason why it's not compatible with quantum mechanics. Or can general relativity be expressed as a quantum field theory?

2) Does the recent flap over tachyons at CERN suggest that something is wrong with our ideas about the speed of light? I'm not only thinking of what might be the speed of light through 730km of rocks. I'm also thinking of the discovery, three years ago, that light of different frequencies arrives from a distant galactic source at different times, and of Magueijo's conjecture that in the early universe the speed of light was higher than it is now, explaining inflation.

3) What do you think of Lee Somlin's argument that because string theory is not background independent, it can't be a candidate for a final theory?

4) I have the impression that finite theories based on the Planck scale would likely avoid zeros and infinities, neatly sidestepping renormalization. Is there any hope that this might be the case?

The more I learn, the more ignorant I seem. Thanks again and best wishes.

Further to my question (2), it seems to me that 1.0245c (or whatever it was) is not big enough to cause real trouble. It suggests a problem in the interpretation of the experiment. A number like 3.0245c could not be explained away so easily.

Why it assumed that the index of refraction (for electromagnetic waves), of the vacuum is exactly one?

If photons interact with the virtual electrons and positrons then it would slow the group velocity of light. Neutrinos which have a much lower interaction cross section might move faster than photons which is c

Dear Prof. Susskind, I am confused about one point at 0:59:35 of Quantum Mechanics Lecture 8 http://www.youtube.com/watch?v=tiXP6dND6SY Shouldn't it here also be an elliptical polarization with a time-varying eccentricity instead of a rotation of linear polarization? Just similar to starting the photon circularly polarized. Actually the choice of alpha(0) and beta(0) doesn't matter much, does it?

Henry,

I answer as a mathematician. Your logic that a past variation from the expected will produce a future correction is flawed. In fact, I would draw the opposite conclusion. Based on the results of your sample, I would bet on aces. It is more likely that the die is not perfect and favors aces based on your experiment. There is no 'memory' in the Law of Large Numbers.

The answer from Henry about the die and aces is not clear to me. It is not the question of the memory of the Law of the Large number. It is the memory of the observer by which an experiment can be repeated over and over again keeping all the parameters fixed with all the precise details. Be it a die or aces.When we shuffle aces we ignore many parameters, which gives rise to the probability. It is here that the probability of the Classical physics fails. But the case is different when statistical probability is applied. In statistics nothing is very much pin-pointed. But the real display of probability starts only at the quantum level, when the very act of observation changes the state of a system. And that is how Uncertainty Principle comes in to play. I need further clarification. Kindly tell from the basics and answer my question pin-pointedly. Not merely replacing die with aces. Answer with die only. Thanks.

Good evening professor Susskind ,in my study I have just come across the fact that Potassium metal do not obey the trends of alkali metal in term of density ,my teacher had hinted me that it have something to do with quantum mechanic but was reluctant to reveal the details,would you mind giving a detail explanation on this

Kiran, I am not a scientist, hence unable to help with yr question, sorry.

ShakeSpear explained (thanks for that) that the Law of Large Numbers does not imply any 'history' or future corrections for past variations.

However I would still like to appreciate comments / info / references, about Time and Probabilities, trying to illustrate my question without any 'law' reference and with a 'perfect system' with all parameters unchanged :

Pls imagine following very simple situation (which could not exist but which can easily been imagined) : a perfect system rolling a perfect die.

In this case, no face is 'favoured' since all parameters remain unchanged. After 5 throws, the last unshown face will necessarily

come out since, if another face had come out more than once earlier, parameters would have changed and the system would not be a perfect one. The uncertainty is just limited to the sequence, of the 5 first outcomes.

Now, if, before the 6th roll / event, the 5 prior throws/outcomes are erased/deleted from the system, the probability for that last face to come out would be reduced from 1/1 to 1/6th as at the start of the experiment, wouldn't it ? Doesn't that reduction show that/how Time / history plays an 'active' role ?

And, more generally, that there are different probabilistic outcomes for each event in a series, according to which past history is considered for that event ?

Doesn't this represent a(n other) macro physic's similarity with quantum mechanics ? = different probabilistic outcomes for the same event for different observers, until the event is realized (like a wave function collapse) ?

Sir, i hav two doubts..

1.what is the difference between relativistic time nd proper time?

2. if the big bang can be compared to what happens when the life of a black hole ends, isnt it equally likely that OUR universe was a huge star in a super big universe?the star just collapsed, led to formation of a black hole, which exploded nd formed our small universe?

Hello sir,

I have a question about proper time in special theory of relativity. I am finding it difficult to understand how is it different from difference between time of events.

Thanks

Projjwal

Dear Henry, Kindly understand my question. If I favor any face (say 5) in the beginning and roll the die measuring all the parameters (like air pressure, torque etc), I will get another event (say face 3). Now I will again favor the face 5 and roll the die for the second time keeping all the parameters (as in the first roll) intact, then I will exactly get back the face 3. This way If we experiment many times favoring face 5 then every time I will get back face 3. Then where is the probability? In big scale (other than quantum), measurements depend on the accuracy of the instruments our ability to keep the parameters constant. The more you are accurate the more you lose grip on probability. But the case is entirely different with the quantum things. This is my question. Kindly clear my doubt.

Hi Leonard

I saw you on Brian Greene's Nova 'Fabric of the Cosmos'. Like many, I am uncomfortable with the asymmetry of an accelerating expansion of the universe and heat death. String theory mentions quantum dimensions, could there not also be additional dimensions on a cosmological scale? Perhaps we are too small to detect them. If so, what looks like an open expansion from a big bang could still end in a big crunch. For example, if we lived on the surface of a balloon: big bang at the opening would end in a big crunch at the nipple. We could test this if we could see really far, since we should be able to see the same distant galaxy looking in opposite directions along the surface of the balloon.

Have physicists/cosmologists considered this sort of idea? It would be fascinating to see computer visualizations of how higher dimensions might be perceived in our limited space-time view. Thank you for your extremely interesting work.

My question is as follows: you make extensive use of the principle of least action in classical mechanics, special relativity, quantum mechanics and even GR. How does one actually come up with the correct form of the lagrangian? Is it educated guess work (insisting on quadratic terms in phi dot for example ) or is it the latter but narrowed down by requiring the form to be gauge invariant (and Lorenz invariant for relativistic situations).

Mathematician's help please!

I'm at lecture 10 of quantum mecanics 00:40:00.When we solve the energy equation for a harmonic oscillator with eigen vector E^-w/2X^2 assuming hbar= 1 the eigen value is w/2 i'm ok with this. But when we keep hbar -h^2/2w^2x^2e^-w/2x^2 doesn't cancell out 1/2w^2x^2e^-w/2x^2?

Where i'm wrong?

Dr. Suskind,

Thanks first for your availability. It reminds me of my freshman year at Stanford in 1967 where my physics professor was Nobel laureate Robert Hofstadter.

I just watched a science channel program on black holes that featured your take on Hawking radiation. When I first heard about loss of information in a black hole, I thought that the complimentary escaping information at the event horizon would provide a signature for the information that was 'lost' so that the information was not really lost, just mirrored and preserved in the discernable universe, which satisfies conservation of energy (information) principles.

The question seems to be: do black holes violate the laws of physics, or do they confirm the laws of physics?

Hi Kiran,to clarify my question, pls imagine a "perfect" simple

coin flipping system (perfect 1/2 heads/tails prob. for a single flip when Time is not involved). When Time(=several flips) is involved, each flip following an odd number of flips gets an additional probability : 1 for the last unshown side, and 0 for the last shown side. No change in accuracy. Macro physics. Which probability applies and why ? In our real, complicated world, mainly based on experience I think, theory says : "the proportion of heads/tails will converge to 1/2 when the number of outcomes approaches infinity ; guaranteeing stable long-term results for random events".

I noticed (Wikipedia) defining present as "eliminator of possibilities that transfers future into past" (yet to be explained however). What's the mechanism behind all this, replacing short term probabilities by aged ones (especially on the long range,

when the nb. of events tends towards infinity), capable of memorizing, converging,eliminating, transmitting (like bosons transmitting forces in Space), in other words, a mechanism preventing chaos, guaranteeing stability ?

Or is it all in the observer's mind ? Would the Anthropic principle be an answer (but wouldn't that be the easy way out?) Hard to find related information! Any comments/info appreciated !

Hi Leonard

I enjoyed seeing you on “Fabric of the Cosmos". Entanglement, superposition and the accelerating expansion of the universe all point to one thing to me. Dimensions beyond the three space and one time dimension that we are familiar with. Since there are several postulated quantum dimensions, additional macro dimensions do not seem too far fetched to me. With a new dimension, our familiar x, y and z axes might distort and behave in unfamiliar ways. Say one axis was curved ever so slightly, immeasurable on our scale but on a cosmological scale it could loop. A collapsing universe could appear to be still accelerating outward if the direction is mis-perceived. Entangled objects appear to act as though connected? Perhaps they are in contact in some undiscovered dimension, a shortcut. Superposition could be different views of the same underlying object due to dimensional distortion, as though seen through the facets of a prism. It should be possible to mathematically model hypothetical dimensions and their effect in our limited worldview, and compare this to what we are seeing.

Basically, it seems to me that instead of coming up with weird and wonderful explanations for what we are seeing whilst clinging to our 3-D worldview, it is our understanding of space(-time) that needs to be revolutionized.

First I would like to thank you for a fantastic resource. Terrific lectures.

My question is with respect to Big Bang cosmology and some astronomical evidence that is quite compelling that appears to invalidate the red-shift/velocity relationship embodied in Hubble's law.

I respect your open-mindedness and depth of knowledge and am very curious to hear your comments.

The evidence I am referring to is best embodied in NGC7603, a Seyfert Galaxy and a companion galaxy, first studied by Halton Arp in the 1960's and more recently (in the early 2000's) once again by several young Spanish astronomers.

The galaxy and its companion are connected by a visible luminescent arm. Within the arm are 2 quasars. The red-shift of these 4 bodies (the 2 galaxies and 2 quasars) have been measured and each one has a very different red-shift.

If the red shift was all due to velocity then the NGC7603 observation

is a miracle of coincidence, since these 4 objects contained in a tiny

speck in the sky, are only apparently associated but are in fact each at

vastly different real positions.

The above case is not unique. Many more such examples have been found (clearly associated objects with markedly distinct red-shifts).

Is it not possible that the observed red-shifts may be in part due to the Compton effect when photons, travelling thru space for long time periods interact with ionized hydrogen or electrons.

Would not such evidence, if correct, invalidate Hubble's law and hence undermine the entire edifice of Big Bang Cosmology?

Anyway, I look forward to your comments and thanks once again for an amazing set of lectures.

Barry Krofchick

Toronto, Canada

First I would like to thank you for a fantastic resource. Terrific lectures.

My question is with respect to Big Bang cosmology and some astronomical evidence that is quite compelling that appears to invalidate the red-shift/velocity relationship embodied in Hubble's law.

I respect your open-mindedness and depth of knowledge and am very curious to hear your comments.

The evidence I am referring to is best embodied in NGC7603, a Seyfert Galaxy and a companion galaxy, first studied by Halton Arp in the 1960's and more recently (in the early 2000's) once again by several young Spanish astronomers.

The galaxy and its companion are connected by a visible luminescent arm. Within the arm are 2 quasars. The red-shift of these 4 bodies (the 2 galaxies and 2 quasars) have been measured and each one has a very different red-shift.

If the red shift was all due to velocity then the NGC7603 observation

is a miracle of coincidence, since these 4 objects contained in a tiny

speck in the sky, are only apparently associated but are in fact each at

vastly different real positions.

The above case is not unique. Many more such examples have been found (clearly associated objects with markedly distinct red-shifts).

Is it not possible that the observed red-shifts may be in part due to the Compton effect when photons, travelling thru space for long time periods interact with ionized hydrogen or electrons.

Would not such evidence, if correct, invalidate Hubble's law and hence undermine the entire edifice of Big Bang Cosmology?

Anyway, I look forward to your comments and thanks once again for an amazing set of lectures.

Barry Krofchick

Toronto, Canada

First I would like to thank you for a fantastic resource. Terrific lectures.

My question is with respect to Big Bang cosmology and some astronomical evidence that is quite compelling that appears to invalidate the red-shift/velocity relationship embodied in Hubble's law.

I respect your open-mindedness and depth of knowledge and am very curious to hear your comments.

The evidence I am referring to is best embodied in NGC7603, a Seyfert Galaxy and a companion galaxy, first studied by Halton Arp in the 1960's and more recently (in the early 2000's) once again by several young Spanish astronomers.

The galaxy and its companion are connected by a visible luminescent arm. Within the arm are 2 quasars. The red-shift of these 4 bodies (the 2 galaxies and 2 quasars) have been measured and each one has a very different red-shift.

If the red shift was all due to velocity then the NGC7603 observation

is a miracle of coincidence, since these 4 objects contained in a tiny

speck in the sky, are only apparently associated but are in fact each at

vastly different real positions.

The above case is not unique. Many more such examples have been found (clearly associated objects with markedly distinct red-shifts).

Is it not possible that the observed red-shifts may be in part due to the Compton effect when photons, travelling thru space for long time periods interact with ionized hydrogen or electrons.

Would not such evidence, if correct, invalidate Hubble's law and hence undermine the entire edifice of Big Bang Cosmology?

Anyway, I look forward to your comments and thanks once again for an amazing set of lectures.

Barry Krofchick

Toronto, Canada

I respect your open-mindedness and depth of knowledge and am very curious to hear your comments.

If the red shift was all due to velocity then the NGC7603 observation

is a miracle of coincidence, since these 4 objects contained in a tiny

speck in the sky, are only apparently associated but are in fact each at

vastly different real positions.

Anyway, I look forward to your comments and thanks once again for an amazing set of lectures.

Barry Krofchick

Toronto, Canada

Please excuse the multiple identical postings :) My mistake

Barry

Prof Susskind,

could you please comment on the work of C.Schiller called the strand model?

Dear professor susskind, i only want to know about String theory, and to some extent about your debate with stephen hawking, kindly reply me as soon ..thnx

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