Thread: Einstein's obsessed question;

It is known by history that Einstein was fascinated by the nature of light,and from age of 16 he constantly questions himself about what he would see if he was to ride on a beam of light? This question stayed with Einstein through is university years(although went to polytechnic of Zurich)!

Einstein soon realize that his question was a basic flaw and that he could not travel at c.

Now let's assume that one could travel at speed c and still retain his human vision and other features but remaining massless so to agree with E=mc2, what will one see? How will the universe appear?

Disclaimer: the above question is not a theoretical valid question but was set up to see what possibly one could see, in other words,to stare ones imagination.

Originally Posted by merumario

Now let's assume that one could travel at speed c and still retain his human vision and other features but remaining massless so to agree with E=mc2, what will one see? How will the universe appear?

I don't see how anyone can possibly know that. It would be pure speculation.

Einstein thought that if he traveled at the same speed next to a light beam (speed c) he would "see" an EM wave (the light wave) at rest and this contradicted Maxwell's equations (all EMR travels at c), thus the Special Theory of Relativity years later.

As the question in the OP involves breaking the laws of physics why would you expect what we know of physics to give a reasonable answer? At best any answer would be groundless, unsupported speculation (aka a waste of time).

Let's suppose that something which cannot happen actually happens. What happens?

It's an unanswerable question.

If someone was travelling at light-speed and he turned on the headlights, what would happen ? This may sound like a good question, but it's not. It's a joke, disguised. There is no way for anything with mass to travel anywhere near this fast; it would require more energy than that which makes-up the universe.

Originally Posted by umbradiago

If someone was travelling at light-speed and he turned on the headlights, what would happen ? This may sound like a good question, but it's not. It's a joke, disguised. There is no way for anything with mass to travel anywhere near this fast; it would require more energy than that which makes-up the universe.

Well, if the person was travelling at infinitesimally less than the speed of light (so a scenario that is not, quite, theoretically impossible), he would see his headlights casting a beam of light as normal, which would propagate away from him at the speed of light, from his point of view. Is that not the point of the invariance of the speed of light? It goes at c relative to you, irrespective of your speed relative to something else.

Very good, exchemist ! I was wrong. It IS a valid scientific question and your explanation is very satisfying as regards Relativity. Maybe there really are no dumb questions. I'll have to try harder.

Originally Posted by umbradiago

Very good, exchemist ! I was wrong. It IS a valid scientific question and your explanation is very satisfying as regards Relativity. Maybe there really are no dumb questions. I'll have to try harder.

Don't beat yourself up, because the original question as stated is in fact outside of the domain of science. That doesn't make it "dumb" but it does make it unanswerable as written. Exchemist rescued the exchange by modifying the question to one that is within the domain of science.

Originally Posted by exchemist

Is that not the point of the invariance of the speed of light? It goes at c relative to you, irrespective of your speed relative to something else.

Einstein wanted to call his theory "Invariance Theory" but "relativity" was the word that stuck.

Originally Posted by PumaMan

Originally Posted by exchemist

Is that not the point of the invariance of the speed of light? It goes at c relative to you, irrespective of your speed relative to something else.

Einstein wanted to call his theory "Invariance Theory" but "relativity" was the word that stuck.

Interesting. Maybe he didn't want to be reminded of his relatives. Who does ?

Originally Posted by exchemist

Well, if the person was travelling at infinitesimally less than the speed of light (so a scenario that is not, quite, theoretically impossible), he would see his headlights casting a beam of light as normal, which would propagate away from him at the speed of light, from his point of view. Is that not the point of the invariance of the speed of light? It goes at c relative to you, irrespective of your speed relative to something else.

I am not sure because we only see light that coming at us and not light going away from us.
I suspect the spectrum shift would be extreme because we would actually be looking at light as if it was being emitted from the things in front of us.

Originally Posted by dan hunter

Originally Posted by exchemist

Well, if the person was travelling at infinitesimally less than the speed of light (so a scenario that is not, quite, theoretically impossible), he would see his headlights casting a beam of light as normal, which would propagate away from him at the speed of light, from his point of view. Is that not the point of the invariance of the speed of light? It goes at c relative to you, irrespective of your speed relative to something else.

I am not sure because we only see light that coming at us and not light going away from us.
I suspect the spectrum shift would be extreme because we would actually be looking at light as if it was being emitted from the things in front of us.

Yes indeed. I was looking at what he person emitting the light would see. From the viewpoint of a viewer travelling at almost c towards the beam (identical to the emitter of the beam travelling at almost c towards that viewer) the doppler shift would be immense - would probably convert the beam from the headlights to gamma rays!

"Dim those brights !" ...is what a former truck driver would say. If there was one here. Aren't gamma the most hi-energy ? Now, the tail lights...would disappear to the stationary observer ? But remain red to an observer moving at c ? Or is everything shifted blue ?

Originally Posted by umbradiago

But remain red to an observer moving at c ?

Nothing moves at c but EMR. If you were traveling at 0.9999999999c and a light beam passed you, you would measure the light beam's speed as c.

I'm trying to comprehend this. Let me ask; what about neutrinos ? these travel at c, as well ? All radiation travels at the same speed as photons ? Is that correct ?

Originally Posted by umbradiago

I All radiation travels at the same speed as photons ? Is that correct ?

EMR = photons. Same thing, different manifestation: wave or particle. All EMR (from radio waves, microwaves, IR, light, UV, x-rays, gamma waves) travels the same speed, c.

Originally Posted by umbradiago

I'm trying to comprehend this. Let me ask; what about neutrinos ? these travel at c, as well ? All radiation travels at the same speed as photons ? Is that correct ?

Neutrinos don't quite travel at c. From the resolution of the solar neutrino problem, we now know that they undergo flavor oscillations, and therefore have mass (of the order of 0.3eV as an upper bound for the sum of the three neutrino masses, if memory serves).

Originally Posted by PumaMan

Originally Posted by umbradiago

I All radiation travels at the same speed as photons ? Is that correct ?

EMR = photons. Same thing, different manifestation: wave or particle. All EMR (from radio waves, microwaves, IR, light, UV, x-rays, gamma waves) travels the same speed, c.

The electromagnetic spectrum, okay. Thanks. Speed, the same; energy/frequency varies, high to low. And a photon is both particle and wave. This is where I pull over and get out the map.

Originally Posted by umbradiago

And a photon is both particle and wave.

Close. A photon is the particle manifestation of EMR.

Here's a relativity thought experiment to confuse you:

A very large space ship takes off from Earth and accelerates (away from Earth) up to 0.9c, relative to the Earth frame of reference.
This first space ship is now traveling at a constant velocity of 0.9c away from Earth, relative to the Earth frame of reference.
The first space ship launches a second (smaller) space ship.
This second space ship accelerates away from the first space ship up to 0.9c, relative to the first space ship's frame of reference.
This second space ship is now traveling at a constant velocity of 0.9c, relative to the the first space ship's frame of reference.
The second now launches a third and the third launches a fourth, and so on.
It is assumed that each ship is launched in the same direction away from the Earth but that really doesn't matter.
It doesn't matter how many launches, the nth space ship will still be going slower than c, relative to the Earth frame of reference.
In fact, it doesn't matter what frame of reference you choose, the speed of light (or any EMR) will always be measured as c.
And matter cannot travel at c.
If you were a passenger in the nth space ship and a light beam passed you, you would measure its speed as c.

And if you think Special Relativity is mind-boggling, try on General Relativity. And these are both "classical" theories. QM is really weird.

Ah, that helps. I will work on digesting that. Been a long time since I've read anything about particle physics and quantum stuff. I didn't really get it then, either. I'm encouraged by something said by a physicist who's name I don't recall, "If you think you understand quantum mechanics, you don't."

Another Special Relativity result is the twin paradox: Twin paradox - Wikipedia, the free encyclopedia

It's good to know that guys as smart as you and others, here, find it "weird", too. I was, in fact, wondering about somehow adding-together two near-light speed sources. Don't worry about confusing me. I like the feeling.

Originally Posted by PumaMan

Here's a relativity though experiment to confuse you:

A very large space ship takes off from Earth and accelerates (away from Earth) up to 0.9c, relative to the Earth frame of reference.
This first space ship is now traveling at a constant velocity of 0.9c away from Earth, relative to the Earth frame of reference.
The first space ship launches a second (smaller) space ship.
This second space ship accelerates away from the first space ship up to 0.9c, relative to the first space ship's frame of reference.
This second space ship is now traveling at a constant velocity of 0.9c, relative to the the first space ship's frame of reference.
The second now launches a third and the third launches a fourth, and so on.
It is assumed that each ship is launched in the same direction away from the Earth but that really doesn't matter.
It doesn't matter how many launches, the nth space ship will still be going slower than c, relative to the Earth frame of reference.
In fact, it doesn't matter what frame of reference you choose, the speed of light (or any EMR) will always be measured as c.
And matter cannot travel at c.
If you were a passenger in the nth space ship and a light beam passed you, you would measure its speed as c.

And if you think Special Relativity is mind-boggling, try on General Relativity. And these are both "classical" theories. QM is really weird.

Originally Posted by umbradiago

It's good to know that guys as smart as you

You're giving me WAY too much credit. The best I might expect is to shine Einstein's shoes -- if he was still alive.

Actually, that little space ship thought experiment can be solved using some (relatively ) simple algebraic equations. I had to work some of those out years ago -- not sure I could still do them.

Velocity addition
List of relativistic equations - Wikipedia, the free encyclopedia

Riding a beam of light. Amazing idea.

Algebra was as far as I got. I like math but have no talent for it. I appreciate that others do. Compliments are free but not everyone gets one. I don't take them back, either. I do apologize quite a lot, though. Sorry.

Originally Posted by PumaMan

Originally Posted by umbradiago

It's good to know that guys as smart as you

You're giving me WAY too much credit. The best I might expect is to shine Einstein's shoes -- if he was still alive.

Actually, that little space ship thought experiment can be solved using some (relatively ) simple algebraic equations. I had to work some of those out years ago -- not sure I could still do them.

Velocity addition
List of relativistic equations - Wikipedia, the free encyclopedia

Many scientists back then did not understand Relativity, others said it couldn't be true, and some hated anything done by a Jewish scientist. Here is a wonderful quote by Einstein in 1931 when a book was published, "100 Authors Against Einstein."

Albert Einstein's response: "If I were wrong, then one would be enough."

http://en.wikipedia.org/wiki/Critici..._of_relativity

[QUOTE=PumaMan;537150]Many scientists back then did not understand Relativity, others said it couldn't be true, and some hated anything done by a Jewish scientist. Here is a wonderful quote by Einstein in 1931 when a book was published, "100 Authors Against Einstein."

Albert Einstein's response: "If I were wrong, then one would be enough."

Criticism of the theory of relativity - Wikipedia, the free encyclopedia[/QUOTE
Thanks. Have you always thought it ironic that the group of people Hitler targeted for ouster were some of the best physicists in Germany; people who might have been able to design an atomic bomb ? More than a few contributing greatly to the Manhattan Project. Einstein's letter to FDR urging the effort, for example.

Originally Posted by umbradiago

Thanks. Have you always thought it ironic that the group of people Hitler targeted for ouster were some of the best physicists in Germany; people who might have been able to design an atomic bomb ? More than a few contributing greatly to the Manhattan Project. Einstein's letter to FDR urging the effort, for example.

Hitler had people working on the bomb too.
Heisenberg was only one of them.
There were other reasons why Germany failed to get a bomb that had nothing to do with the quality of their physicists.

Originally Posted by umbradiago

"Dim those brights !" ...is what a former truck driver would say. If there was one here. Aren't gamma the most hi-energy ? Now, the tail lights...would disappear to the stationary observer ? But remain red to an observer moving at c ? Or is everything shifted blue ?

Indeed, I think the tail lights would appear red-shifted to microwaves or something, to an observer behind, from whom the light source was retreating.

But in both cases, extreme Doppler shift notwithstanding, the speed of the light reaching either observer would still be c.

Furthermore, if I remember correctly (and being only a chemist rather than a physicist I may not), the most interesting case is actually an observer to the side of the moving source of light, and across whose field of view the source is travelling at close to c. The spaceship or vehicle will - I think- appear to such an observer to have turned partly sideways on, rotating away from the observer, so that less of the front is visible and more of the back. This is a consequence of the appreciable motion of the object while the photons from front and back are in flight.

But as I say, I'd quite like a real physicist to comment on this.

Originally Posted by merumario

Now let's assume that one could travel at speed c and still retain his human vision and other features but remaining massless so to agree with E=mc2, what will one see? How will the universe appear?

The question is meaningless, and has no answer.
The only thing one could do is extrapolate known and established laws into a domain where they aren't technically valid. If you do that, then the "light rider" will see nothing at all, and the entire universe is length contracted to zero size along his direction of travel. This means that observer would determine himself to be everywhere along his trajectory at once, and the notion of separate events would cease to make sense for him. He would be in a static universe where the concept of time is meaningless, and where one spatial dimension is of size zero; he would basically be caught on a 2-dimensional surface like a cartoon character, but all other points on that surface are forever out of reach for him.

This is the classical version - much more interesting to me would be what happens if you fully account for quantum effects, but then things get very complicated. I shall think about it a bit

Will be waiting for that.

Originally Posted by Markus Hanke

Originally Posted by merumario

Now let's assume that one could travel at speed c and still retain his human vision and other features but remaining massless so to agree with E=mc2, what will one see? How will the universe appear?

The question is meaningless, and has no answer.
The only thing one could do is extrapolate known and established laws into a domain where they aren't technically valid. If you do that, then the "light rider" will see nothing at all, and the entire universe is length contracted to zero size along his direction of travel. This means that observer would determine himself to be everywhere along his trajectory at once, and the notion of separate events would cease to make sense for him. He would be in a static universe where the concept of time is meaningless, and where one spatial dimension is of size zero; he would basically be caught on a 2-dimensional surface like a cartoon character, but all other points on that surface are forever out of reach for him.

This is the classical version - much more interesting to me would be what happens if you fully account for quantum effects, but then things get very complicated. I shall think about it a bit

Here is such a paper.

Just because we cannot travel at c does not mean we can't model what long streams of photons would look like at a discrete instances of time. We could start by working back from the solution by viewing the 'light rider' as the constant streams of photons being emitted from sources as they rotate around a stationary center of mass.

You can view the 'light rider's form in Euclidean space by plotting the positions from the locations where the photons were emitted over one complete cycle and moving them towards the observer in a straight line. These photon streams exist at a discrete instance in time and all the x, y and z axis are measured in units of time so that c is truly invariant in this time-space. This pattern (for 45 degree tilt) will appear when the total distance from the rotating sources to the observer equals 2 * Pi * r * c/v, the sources continue to emit photons and rotate for one complete cycle, and the photon paths are not blocked or distorted. The colors of the paths reflect the direction of the source with respect to the observer when the photons were emitted. The distance from the observer to the center of mass equals r * sqrt[((2 * Pi * c)/v)^2 -1] after one complete rotation and all of the photons in the paths will pass through the observer if it remains stationary at this distance from the center of mass.


After one quarter of rotation the source originally at 1,0 has moved to 4,0 and the source originally at 3,0 has moved to 2,0.
After two quarters of rotation the source at 4,0 has moved to 3,0 and the source at 2,0 has moved to 1,0.
After three quarters of rotation the source at 3,0 has moved to 2,0 and the source at 1,0 has moved to 4,0.
After four quarters of rotation the source at 2,0 has moved back to its original position 1,0 and the source at 4,0 has moved back to its initial position 3,0.

Originally Posted by merumario

Now let's assume that one could travel at speed c and still retain his human vision and other features but remaining massless so to agree with E=mc2, what will one see? How will the universe appear?

What can be taken out from this proposal is that the entire causal history available to an observer is defined instantaneously (from the frame of reference of a photon) by all the information contained within the observers defined hubble volume. If the entire information state of that hubble volume can be defined as a quantum wavefunction, then the instantaneous collapse of that wavefunction would define a classical universe from the frame of reference of that observer.

I think that this is the general thrust being sought from LQG theories such as Causal Dynamic Triangulation. While it is non-sensical in relativity terms to talk of riding a photon from the frame of reference of an observer, the instantaneous access to the information contained within the entire universe is very useful to quantum mechanics and in current attempts to unify GR and QM through Quantum Gravity approaches.

By adopting an observer dependent context to the information exclusively available to a single observer, this approach overcomes some of the issues associated with the 'static' nature of the Wheeler-DeWitt equation (Universal Quantum Wavefunction) and is actively being pursued at Stanford in QG theoretical research. In essence the multiverse approach in String Theory is being replaced by a multi-observer viewpoint in LQG defined by the frame of reference taken from each point in spacetime.