Surpassing the speed of light? Why not?

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Discussion Overview

The discussion revolves around the possibility of surpassing the speed of light, exploring the implications of the laws of physics in different inertial frames of reference. Participants examine the nature of wave propagation, the differences between sound and light, and the mathematical underpinnings of relativistic physics.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that the speed of any wave is constant in all inertial frames, questioning why mass could not exceed the speed of light.
  • Others argue that no matter how much energy is added to mass, its speed will remain below the speed of light, referencing relativistic velocity addition.
  • There is a discussion about the differences between sound and light, with some noting that sound requires a medium and its speed is not invariant across reference frames, unlike light.
  • Participants mention the implications of time dilation and redshift/blue shift in relation to the speed of light, suggesting that these phenomena are consistent with the idea that mass cannot exceed light speed.
  • Some express confusion about the application of classical kinetic energy formulas in relativistic contexts, emphasizing that such formulas are approximations and not applicable at relativistic speeds.
  • There are claims that the wavelength of light changes based on the motion of the source, similar to sound, but others challenge this comparison, stating that the fundamental nature of light differs significantly from sound.
  • Questions are raised about measuring speeds in different reference frames and how this relates to the invariance of the speed of light.

Areas of Agreement / Disagreement

Participants generally disagree on the possibility of surpassing the speed of light, with some supporting the idea and others firmly rejecting it based on established relativistic principles. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Participants express uncertainty regarding the application of classical physics in relativistic scenarios and the implications of wave behavior in different media. There are unresolved questions about the measurements of speed and the nature of energy transfer in wave propagation.

quincy harman
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The first postulate is perfect, the laws of physics are the same for all uniform inertial frames of reference. In fact the second postulate is perfect as well the speed of light is constant in all uniform inertial frames of reference. But here is my problem with it, the speed of any wave is constant in all inertial frames of reference. By adding speed all you're doing is giving the wave energy in the direction of motion and taking energy from it the opposite direction. So why would mass not be able to exceed the speed of light? Especially when the laws of physics are the same in all inertial reference frames. This means all motion is relative.When you surpass the speed of sound you get a sonic boom because the said object is moving to fast for the wave to keep up. But for the speed of sound we don't measure v-s or v+s, where s = speed of sound, like we would in classical mechanics but we don't calculate time dilation from it. I see a problem here. Mass cannot force light to accelerate but this doesn't necessarily mean mass cannot surpass a photon. If the laws of physics are the same in all reference frames once we we reach escape velocity why wouldn't we be able to reach speeds beyond the speed of light?
 
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quincy harman said:
By adding speed all you're doing is giving the wave energy in the direction of motion and taking energy from it the opposite direction.
There is no "direction-dependent energy" where you could take something away.
quincy harman said:
So why would mass not be able to exceed the speed of light?
No matter how much energy you give the mass, its speed will be below the speed of light.
quincy harman said:
This means all motion is relative.
Correct.

Sound is propagating in a medium and the speed relative to observers depends on their motion, this is completely different from light.
quincy harman said:
If the laws of physics are the same in all reference frames once we we reach escape velocity why wouldn't we be able to reach speeds beyond the speed of light?
No matter how long and how intense you accelerate, the result is always a speed below the speed of light.
You can verify this with the formula for url=https://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity]relativistic velocity addition[/url]. Take some starting speed, assume your rocket accelerates by 10m/s^2 for one second, add this to the starting speed with the relativistic formula, see how much the speed changes: it will be less than 10m/s. You can keep adding those speed increments and you will never surpass the speed of light.
 
mfb said:
There is no "direction-dependent energy" where you could take something away.
No matter how much energy you give the mass, its speed will be below the speed of light.Correct.

Sound is propagating in a medium and the speed relative to observers depends on their motion, this is completely different from light.
No matter how long and how intense you accelerate, the result is always a speed below the speed of light.
You can verify this with the formula for url=https://en.wikipedia.org/wiki/Velocity-addition_formula#Special_relativity]relativistic velocity addition[/url]. Take some starting speed, assume your rocket accelerates by 10m/s^2 for one second, add this to the starting speed with the relativistic formula, see how much the speed changes: it will be less than 10m/s. You can keep adding those speed increments and you will never surpass the speed of light.
Red shifting if it is moving away from you blue shifting it is moving toward you, +frequency=+energy, and I understand m0/sqrt 1-v2/c2 is why it is currently thought that no mass can exceed the speed of light, same for time dilation, but the math is based off the idea that you cannot measure light with v+c,v-c, light oscillates through electromagnetic fields similar to the way sound oscillates through a medium by which I mean If a moving object can give a energy too light in the same way as it can sound, how is it different? If an object is moving towards you at 99.99% the speed of light you wouldn't see anything because it would be beyond the visible wavelength spectrum. Same if it was moving away from you. If the laws of physics are universal in all inertial frames of reference then K=1/2mv^2 is all it would take to accelerate at all velocities but relative to what? Why are the clock rates different?
 
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quincy harman said:
but the math is based off the idea that you cannot measure light with v+c,v-c
And this is based on experimental results, yes. Those results are extremely precise.
quincy harman said:
light oscillates through electromagnetic fields similar to the way sound oscillates through a medium
This is not similar at all.
quincy harman said:
If the laws of physics are universal in all inertial frames of reference then K=1/2mv^2 is all it would take to accelerate at all velocities but relative to what?
That formula is a nonrelativistic approximation, you cannot use it in relativity.
quincy harman said:
Why are the clock rates different?
Otherwise the speed of light could not be constant. But again, it is based on measurements. All special relativistic effects have been measured extremely well.
 
quincy harman said:
Red shifting if it is moving away from you blue shifting it is moving toward you, +frequency=+energy, and I understand m0/sqrt 1-v2/c2 is why it is currently thought that no mass can exceed the speed of light, same for time dilation, but the math is based off the idea that you cannot measure light with v+c,v-c, light oscillates through electromagnetic fields similar to the way sound oscillates through a medium by which I mean If a moving object can give a energy too light in the same way as it can sound, how is it different? If an object is moving towards you at 99.99% the speed of light you wouldn't see anything because it would be beyond the visible wavelength spectrum. Same if it was moving away from you. If the laws of physics are universal in all inertial frames of reference then K=1/2mv^2 is all it would take to accelerate at all velocities but relative to what?
mfb said:
And this is based on experimental results, yes. Those results are extremely precise.This is not similar at all.That formula is a nonrelativistic approximation, you cannot use it in relativity.Otherwise the speed of light could not be constant. But again, it is based on measurements. All special relativistic effects have been measured extremely well.
You didn't finish reading what I said about why they are similar. They are similar because wavelength changes from the object emitting them based on the direction of motion. Of course the speed of light isn't going to oscillate the same. One oscillates threw electric and magnetic fields while another oscillates through a medium. Also I'm want to make it very clear I'm not denying the consistency of c and if you think that you're missing my point. My point is c in vacuum is just a product of waves. wavelength*frequency=speed, I also understand that sound travels at different speeds in different mediums but given a medium ^
Also you didn't answer my question can you measure the speed of the object and the speed + the speed of sound?
 
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quincy harman said:
light oscillates through electromagnetic fields similar to the way sound oscillates through a medium by which I mean If a moving object can give a energy too light in the same way as it can sound, how is it different?
The key difference is that the speed of a sound wave is not invariant. Different reference frames disagree on how fast a given sound wave is moving. That is not at all the same as with light.

Suppose there is a lightning strike near where I am on the ground and you are in a supersonic aircraft passing overhead. We will both agree on the speed of the light, but not on the speed of the thunder.
 
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quincy harman said:
They are similar because wavelength changes from the object emitting them based on the direction of motion.
Wavelength in which frame?
The answers are completely different for light and for sound.
quincy harman said:
My point is c in vacuum is just a product of waves.
It is not.
There is a fundamental speed in special relativity - this has nothing to do with light.
Light happens to travel at this fundamental speed, for purely historical reasons we call this speed "speed of light".
quincy harman said:
Also you didn't answer my question can you measure the speed of the object and the speed + the speed of sound?
You can measure every speed. I don't understand what the question is.
 
quincy harman said:
You didn't finish reading what I said about why they are similar. They are similar because wavelength changes from the object emitting them based on the direction of motion. Of course the speed of light isn't going to oscillate the same. One oscillates threw electric and magnetic fields while another oscillates through a medium.
Also you didn't answer my question can you measure the speed of the object and the speed + the speed of sound?
quincy harman said:
You didn't finish reading what I said about why they are similar. They are similar because wavelength changes from the object emitting them based on the direction of motion. Of course the speed of light isn't going to oscillate the same. One oscillates threw electric and magnetic fields while another oscillates through a medium. Also I'm want to make it very clear I'm not denying the consistency of c and if you think that you're missing my point.
Also you didn't answer my question can you measure the speed of the object and the speed + the speed of sound?
My point is that the consistency of c is just a product of waves and not time dilation or length contraction.
DaleSpam said:
The key difference is that the speed of a sound wave is not invariant. Different reference frames disagree on how fast a given sound wave is moving. That is not at all the same as with light.

Suppose there is a lightning strike near where I am on the ground and you are in a supersonic aircraft passing overhead. We will both agree on the speed of the light, but not on the speed of the thunder.
Doesn't that have to do with location? and light being much faster?
 
mfb said:
Wavelength in which frame?
The answers are completely different for light and for sound.
It is not.
There is a fundamental speed in special relativity - this has nothing to do with light.
Light happens to travel at this fundamental speed, for purely historical reasons we call this speed "speed of light".
You can measure every speed. I don't understand what the question is.
you cannot measure the speed of the object that the wave is coming from + the speed of the wave
 
  • #10
okay I think I get it, the speed of light appears instantaneous for all observers because it doesn't travel through time even though it has a finite speed through space?
 
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  • #11
quincy harman said:
Doesn't that have to do with location? and light being much faster?
No, it is a fundamental difference in the behavior of light and sound.
 
  • #12
quincy harman said:
okay I think I get it, the speed of light appears instantaneous for all observers? Because it doesn't travel through time?
DaleSpam said:
No, it is a fundamental difference in the behavior of light and sound.
how does no time pass for the photon yet we observe a finite speed for light?
 
  • #13
quincy harman said:
okay I think I get it, the speed of light appears instantaneous for all observers
No, it doesn't.

quincy harman said:
because it doesn't travel through time even though it has a finite speed through space?
?
 
  • #14
Doc Al said:
No, it doesn't.?
no time passes for light because it has no rest frames
 
  • #15
There is no notion of time for photon - because there is no reference frame of photon.

"no time passes for light because it has no rest frames"

No notion of time does not mean "no time passes". It means that you can't say anything meaningful about time for photon. It is a difference. There has been a lot of threads discussing that issue, search for them.
 
  • #16
Most of the OP has to do with why c is frame-independent, rather than why you can't go faster than that. We have a FAQ on that topic: https://www.physicsforums.com/threads/why-is-the-speed-of-light-the-same-in-all-frames-of-reference.534862/

The discussion of waves is based on a common misconception that relativity, and c, are fundamentally related in some way to light waves. They aren't. See http://physics.stackexchange.com/q/35404/4552 .

Re why you can't go faster than c, see http://physics.stackexchange.com/a/61129/4552 . It has nothing to do with light waves, because neither c nor relativity have anything to do with light waves.
 
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  • #17
quincy harman said:
how does no time pass for the photon yet we observe a finite speed for light?
The statement that no time passes for a photon is not correct, although it does crop up from time to time in pop-sci works from authors who should know better.
 
  • #18
weirdoguy said:
There is no notion of time for photon - because there is no reference frame of photon.

"no time passes for light because it has no rest frames"

No notion of time does not mean "no time passes".
we see the photon as it left 14 billion light years ago. if you were a photon you would not experience time. but we observe it as moving through space at a finite speed
DaleSpam said:
The statement that no time passes for a photon is not correct, although it does crop up from time to time in pop-sci works from authors who should know better.
well thank you for making fun of me :)
 
  • #19
quincy harman said:
well thank you for making fun of me :)
Hi Quincy Harman, I am not sure what I said that could have been interpreted as making fun of you. I certainly am not doing so.
 
  • #20
DaleSpam said:
Hi Quincy Harman, I am not sure what I said that could have been interpreted as making fun of you. I certainly am not doing so.
can you explain what a rest frame please?
 
  • #21
quincy harman said:
can you explain what a rest frame please?
A rest frame is a reference frame where a given object is at rest. In other words, its velocity is 0 in that frame.
 
  • #22
DaleSpam said:
A rest frame is a reference frame where a given object is at rest. In other words, its velocity is 0 in that frame.
and a frame is a specific point in space and time?
 
  • #23
quincy harman said:
and a frame is a specific point in space and time?
No, a frame in special relativity is a coordinate system. So it extends over all of spacetime. In GR the definition is more technical, but typically GR frames also cover all of spacetime.
 
  • #24
quincy harman said:
can you explain what a rest frame please?

The term "The rest frame of <something>" means "a frame in which that <something> is not moving". Choose a coordinate system in which your ##x##, ##y##, and ##z## coordinates are not changing (but of your course your ##t## coordinate is changing, as it must in all frames) and you've chosen your own rest frame.

One implication of this definition is that light in a vacuum has no rest frame - it moves at speed ##c## in all frames, so there is no frame in which it is not moving.
 
  • #25
quincy harman said:
and a frame is a specific point in space and time?

There is a classic film that might help here:





It's necessary to have a clear understanding of this sort of thing in the pre-relativity context before one can understand relativity. That's why physics classes do Newtonian mechanics and frames of reference first, and relativity later.
 
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  • #26
quincy harman said:
we see the photon as it left 14 billion light years ago.
Years ago, not light years. It gets redshifted and its direction gets influenced by gravity. We could also see massive neutrinos as they were emitted 13.7 billion years ago - our detectors are just not sensitive to them (yet?), but this is not a fundamental problem.
 
  • #27
we are always consider 0- 300,000 km , but all things are moving and matter too, What are the things clash to can not move more speed light?
 
  • #28
I don't understand that question.
 
  • #29
Jose Leal said:
we are always consider 0- 300,000 km , but all things are moving and matter too, What are the things clash to can not move more speed light?
If you are simply asking "what stops an object from moving faster than the speed of light?", to answer that, you need to learn the theory of relativity. There is no simpler explanation.
 

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