Value of c and strange things that don't happen when at c

[ZirkMan]

Hi there,

I became really serious studying the basic principles of physics few months ago. There is a plenty of good study material out there, so there was no need to ask anybody anything. Until now.

The problem is with the speed of light c and why it has properties and value it has.
Few questions which I would like to elaborate:

1. Is there really no theory or framework from which I can calculate the value of speed of light without knowing in advance what it value should be nor by measuring it directly?

2. The basic principle of the Special relativity is that all observers perceive a light wave move at c regardless of their relative speeds to each other and to the light source. So it must be true that if you reverse it, relative to a light wave all (matter) objects move with one speed the c. For a light wave this would be as real as it gets. If matter moves at c, it's mass becomes infinite and time in the matter world stops for the observer (it essentially becomes a singularity. I quess that's why there is the fear that LHC will create miniscule black holes by accelerating some particles too close to the speed of light).
If this reversal of perspective is true, why the path of light rays we see doesn't act as if any mass object it encounters was a singularity?

 

[ramparts]

Hi there,

I became really serious studying the basic principles of physics few months ago. There is a plenty of good study material out there, so there was no need to ask anybody anything. Until now.

The problem is with the speed of light c and why it has properties and value it has.
Few questions which I would like to elaborate:

1. Is there really no theory or framework from which I can calculate the value of speed of light without knowing in advance what it value should be nor by measuring it directly?

No. As far as we know, the speed of light is a fundamental constant of our universe. If you think about it, we need to have at least one of those, otherwise there's nothing to calculate the other "constants" from! So it's possible there's some deeper constant from which we can derive the speed of light, but none we know of or have predicted so far.

2. The basic principle of the Special relativity is that all observers perceive a light wave move at c regardless of their relative speeds to each other and to the light source. So it must be true that if you reverse it, relative to a light wave all (matter) objects move with one speed the c. For a light wave this would be as real as it gets. If matter moves at c, it's mass becomes infinite and time in the matter world stops for the observer (it essentially becomes a singularity. I quess that's why there is the fear that LHC will create miniscule black holes by accelerating some particles too close to the speed of light).
If this reversal of perspective is true, why the path of light rays we see doesn't act as if any mass object it encounters was a singularity?

This is getting really speculative, but if matter were to move at the speed of light, it wouldn't become a singularity. This thought experiment is supposed to show that it's impossible to make matter move at c (rather than what happens if matter moves at c). Photons (light particles) don't perceive time so none of this matters for them - we can't really talk about "their perspective".

 

[ZirkMan]

No. As far as we know, the speed of light is a fundamental constant of our universe. If you think about it, we need to have at least one of those, otherwise there's nothing to calculate the other "constants" from! So it's possible there's some deeper constant from which we can derive the speed of light, but none we know of or have predicted so far.

OK, case solved. Thanks for an elegant and true reply.

This is getting really speculative, but if matter were to move at the speed of light, it wouldn't become a singularity. This thought experiment is supposed to show that it's impossible to make matter move at c (rather than what happens if matter moves at c). Photons (light particles) don't perceive time so none of this matters for them - we can't really talk about "their perspective".

OK, I switch from impossible to possible frame of reference of an observer with a nonzero rest mass and relative speed of 0.999c (which has a meaning now). All other mass objects I would encounter with this relativistic speed would have a relative mass (due to the relativistic effect of energy having mass) much higher as when I was in rest in relation to them.
My question is if this higher mass will effect the gravitation of those objects so that they will attract me with much higher gravity than if I was in a state of rest in relation to them? If not, why is gravitational field not relative to speed?

 

[darkmatter4brains]

c is not the only fundamental constant that appears in physics with no real explanation, or more fundamental theory from which it can be derived. hbar, from quantum mechanics is another.

Actually, the fine structure constant is considered the most fundamental constant (that we know of). One reason is that it is a comglomeration of the speed of light, hbar and the fundamental unit of charge. The most important reason is that it is dimensionless, no matter what system of units you choose to use. It is often called a god-given number.

But once again, nobody knows where it "comes from". I think it was Feynman that said if we could figure out where the fine sturcture constant comes from, we'd know everything. This constant shows up in QM and is very prevalent in QED as well.

Physicists do have hopes that some more fundamental theory will come along from which you will be able to "derive" these constants. We'll just have to wait and see ...

The fine-tuned values of these constants also factor into numerous debates because, if they were slightly different, life would not exist and, in fact, the Universe would be MUCH different.