A question about the speed of light and electromagnetism

[PeroK]

I'm not convinced that the oversimplification that time is not passing in the reference frame of a particle with no rest mass has no use.

The reference to particle decay is interesting, but we were trying to establish the kinematics of light in relativity. Light is studied using an affine parameterisation (so we don't need proper time along a light-like trajectory). Ironically, many of the tests of GR are experiments involving light: the Pound-Rebka experiment; Eddington's original experiment using a solar eclipse; the Shapiro delay. So, far from being problematic, the kinematics of light are well understood and modelled within relativity, and provide many of the key tests of the theory.

 

[PeterDonis]

the reference frame of a particle with no rest mass

There is no such thing. It is impossible to have a reference frame in which a zero rest mass object is at rest.

You can have a coordinate chart in which the worldline of a zero rest mass object is one of the coordinate axes. But that chart will not meet the requirements for a reference frame, because it is impossible to construct an orthonormal frame field using that coordinate chart's basis vectors.

 

[PeterDonis]

This oversimplification could be useful in understanding why individual photons, gluons, and gravitons do not decay, no matter how much energy they carry.

No, it isn't, because even though the spacetime arc length along the worldlines of such particles is zero, those worldlines still consist of distinct events, and a decay could still happen at any of those events, if all we are looking at is the spacetime geometry. To explain why decays do not happen at any of those events, you have to show that the amplitude for such decays is zero at all of those events; and just showing that the arc length along the worldline is zero is not sufficient to do that.

none of the forces carried by zero rest mass bosons do experience CP violation.

I don't think this is true. Above the electroweak symmetry breaking threshold, the electroweak gauge bosons are massless, but AFAIK they can still induce CP violating interactions.

 

[Mister T]

I'm not convinced that the oversimplification that time is not passing in the reference frame of a particle with no rest mass has no use.

It may have some use, but it's still an oversimplification and is the source of a lot of misunderstanding.

 

[johnfrancismurray]

We should be cautious about this line of argument. The standard formulas of SR are derived using assumptions that imply that $v\lt c$ so cannot be expected to apply when it is not. Thus the infinities that appear in these standard formulas when we plug in $v=c$ (and likewise the negative numbers that appear under a square root sign when we plug in $v\gt c$) aren't telling us anything about how the world works, they're the math telling us that we're misusing it.

I'm happier with the argument that no matter how much energy we add to an object initially at rest relative to us, the resulting speed of the object relative to us will be less than $c$. This result follows from the velocity addition rule without introducing any infinities or trying to make sense out of a division by zero.

Thank you Nugatory, it's a very good point that you have made here and if other contributors from this thread are reading I want to pass on a thankyou to all of them also. Although I feel like my original statement and idea still stands up and is important I have learnt a lot from reading all the responses that overwhelmingly state that it should not be, is not, or is not relevant to an overall picture.
When I have time I can make my point again from a better position with the appropriate language. But if I may leave you with a thought for consideration as you have with me, it is that infinity has a very important function and is vital to the possibility of a universe and is not a place where the maths breaks down and speculation is out of bounds.
many thanks and hope 2025 is a great year for all
john

 

[phinds]

Although I feel like my original statement and idea still stands up

It would appear that you have not taken in what you have been told. Your original idea "an observation that light has both a 'true' and 'apparent' speed." most emphatically does NOT stand up and changing the language isn't going to change that.

Also, in physics, usually infinity IS the place where our models break down. To claim otherwise, in those cases, is pointless.

 

[Nugatory]

Thread is open again after a bit of minor cosmetic surgery to clean up confusing quoting

 

[Dale]

But if I may leave you with a thought for consideration as you have with me, it is that infinity has a very important function and is vital to the possibility of a universe and is not a place where the maths breaks down and speculation is out of bounds.

The concept of infinity is pretty well understood. It is not part of the real numbers, but there are infinite hyperreal numbers.

However, be aware that even though the hyperreals have infinite numbers, division by 0 is still undefined.

 

[Hornbein]

But I assume that you are NOT implying that a photon does experience (zero) time.

It depends on what you mean by experiencing zero time. I'd say that time depends on change. We able to perceive time because things change. A photon hits some rhodopsin in the the retina which causes it to change. If our body were completely unchanged then we could not perceive anything, could not think, and would have no concept whatsoever of time or anything else for that matter. Neither could a static observer use us to measure time. Something that isn't moving and never changes -- seems timeless to me. Similarly, if there is a completely empty Universe then there is no such thing as time. It never changes at all so how could anyone say that time is passing there.

AE said "time is what a clock measures." If clocks of any sort cannot exist (stopped clocks don't count) is there such a thing as time?

As far as we know a photon doesn't change at all until it is absorbed and ceases to exist. This is why we can see clearly galaxies billions of years old. So I think it is fair to say the photon doesn't experience time. An observer may be able to measure the movement of pulses of light, but the photon doesn't know anything about that so it is the observer experiencing time, not the photon.

How about a Universe with nothing but photons that don't interact? If there were an observer there they might see change. But there is no observer there. So is time passing or isn't it? I dunno.

 

[renormalize]

How about a Universe with nothing but photons that don't interact? If there were an observer there they might see change. But there is no observer there. So is time passing or isn't it? I dunno.

Consider an expanding universe like ours, but filled with nothing but the photons of the cosmic background radiation. According to physics, that radiation continuously reddens, which corresponds to the passage of time, even with no observers.
Or are you pondering philosophy, like whether a falling tree makes a sound when there's no observer around to hear it?

 

[phinds]

It depends on what you mean by experiencing zero time. I'd say that time depends on change. We able to perceive time because things change. A photon hits some rhodopsin in the the retina which causes it to change. If our body were completely unchanged then we could not perceive anything, could not think, and would have no concept whatsoever of time or anything else for that matter. Neither could a static observer use us to measure time. Something that isn't moving and never changes -- seems timeless to me. Similarly, if there is a completely empty Universe then there is no such thing as time. It never changes at all so how could anyone say that time is passing there.

AE said "time is what a clock measures." If clocks of any sort cannot exist (stopped clocks don't count) is there such a thing as time?

As far as we know a photon doesn't change at all until it is absorbed and ceases to exist. This is why we can see clearly galaxies billions of years old. So I think it is fair to say the photon doesn't experience time. An observer may be able to measure the movement of pulses of light, but the photon doesn't know anything about that so it is the observer experiencing time, not the photon.

How about a Universe with nothing but photons that don't interact? If there were an observer there they might see change. But there is no observer there. So is time passing or isn't it? I dunno.

As far as I can tell, none of that has anything at all to do with whether or not a photon experiences time.

 

[weirdoguy]

When I have time I can make my point again from a better position with the appropriate language.

Please don't. Your point has been refuted over and over again. It's not a matter of opinion, it's a matter of facts. Facts are against your point. Period.

Similarly, if there is a completely empty Universe then there is no such thing as time.

Nonsense. And I don't even see why someone with so many posts would even say such things. You should know better.

 

[jbriggs444]

I'm not convinced that the oversimplification that time is not passing in the reference frame of a particle with no rest mass has no use.

Any sentence involving "the reference frame of a particle with no rest mass" is sure to be nonsense. There is no such reference frame.

It is a classic blunder. Like "Never go up against a Sicilian when death is on the line".

 

[PeroK]

It is a classic blunder. Like "Never go up against a Sicilian when death is on the line".

Are you talking about chess?

 

[jbriggs444]

Are you talking about chess?

Popular movie reference.

 

[PeroK]

Popular movie reference.

Ah, okay. Personally, I'd be more worried by the King's Indian Defence.

 

[DaveC426913]

Are you talking about chess?

PeroK inadvertently reveals he is not actually an Earthling...