Wave

[Speakpigeon]

As I understand it, time isn't supposed to elapse for anything moving at speed c, and therefore, in particular, for photons. However, light is also supposed to be an electromagnetic wave, i.e. essentially a wave of orthogonal magnetic and electric magnitudes moving at c in a vacuum.

I'm not entirely sure how this is supposed to go, however.

As I see it, a wave is a propagation of a quantity in a medium, but an electromagnetic wave is a propagation in spacetime, which is supposed to be nothing else but all events considered collectively. The only things which seem changing in the case of light are the magnetic and electric magnitudes at the location the wave is moving across. However, there seems to be two possible scenarios...

One scenario, (A), is as follows. Let's assume that at a point x in space and just before the front of a light wave gets there at t0, the magnetic and electric magnitudes are zero or near zero. When the front of the wave gets to x, the magnetic and electric magnitudes will take one particular value each and those two values will no change as the wave moves across point x. I think that's called a stationary wave...

In a second scenario, (B), the wave is moving as a block so that the values of the magnetic and electric magnitudes at point x will keep changing according to which part of the wave is moving across this point.

It may be a bit complicated to understand like this, so a nice picture might help:

​

So, in the case of light propagating "freely" through space, in a vacuum, which of the scenarios A and B is the correct one?

Or is it something else altogether?

Thanks,
EB

 

[ryan]

I believe they are like ocean waves because layered onto space-time are fields. 2 of those fields are the electric and magnetic fields. These fields are like 2 "oceans" overlapping for anything that can influence them such as a charged particle.

 

[steve_bank]

In general a wave is anything propagating that is periodic. A square or triangle wave as opposed to a sine wave.

EM propagates as an oscillation. Energy cyclically transfer between electric and magnetic fields. The sinusoidal variation in an EM wave can be measured in a device called a slotted transmission line.

There are two types of waves, transverse and longitudinal.

EM waves are transverse, the power vector is orthogonal to the direction of travel. The Poynting Vector.

Air is a longitudinal wave, as is a slinky toy. The power vector is in line with the direction of propagation. Hit a metal rod with a hammer on one end and the wave is longitudinal. Lay a slinky out and give one end a push.

Standing waves in EM can be set up on a transmission line. Analogous to a QM potential well and a particle.

Imagine light prop gating from a distant star. The wave front is a sphere expanding around the star at C. If you are at a stationary point relative to the star you will see a sinusoidal variation in amplitude as the wave passes. If a pulsed laser burst passes you by you will see a rectangular amplitude change and within the pulse a sine wave. In QM a wave packet.

 

[Speakpigeon]

A or B?
Or some C?
EB

 

[fast]

As I understand it, time isn't supposed to elapse for anything moving at speed c, and therefore, in particular, for photons.

Science has that wrong. That’s not to say their math is incorrect or useless. Science has hi-jacked the term, “time.” Time is not what they say it is. Their calculators and formulas are just fine. It’s just their word choice that has fallen short.

Time is independent of motion. Time neither slows nor speeds up. It’s perfectly rhythmic. Confuse not the worldly movements that allows for our sense of time and time itself.

Thought experiment: (but, get it right): at a spaceship speed of c-c (0 m/s in a vacuum, or oh say outer space as a proxy), light shall not exceed c, and your measurements of a second will not be illusory. If you increase your speed, c will not change; therefore, you will approach the speed of light. But, substantively increase your speed and do some measurements. It will appear to the observer in their frame of reference that light is traveling at c (and strangely enough, they’d be right), but everything else is distorted. It’s not time and distance that has changed. Time has not dilated. Our perceptions become distorted, and the math shows by how much.

 

[Speakpigeon]

As I understand it, time isn't supposed to elapse for anything moving at speed c, and therefore, in particular, for photons.

Science has that wrong. That’s not to say their math is incorrect or useless. Science has hi-jacked the term, “time.” Time is not what they say it is. Their calculators and formulas are just fine. It’s just their word choice that has fallen short.

Time is independent of motion. Time neither slows nor speeds up. It’s perfectly rhythmic. Confuse not the worldly movements that allows for our sense of time and time itself.

Thought experiment: (but, get it right): at a spaceship speed of c-c (0 m/s in a vacuum, or oh say outer space as a proxy), light shall not exceed c, and your measurements of a second will not be illusory. If you increase your speed, c will not change; therefore, you will approach the speed of light. But, substantively increase your speed and do some measurements. It will appear to the observer in their frame of reference that light is traveling at c (and strangely enough, they’d be right), but everything else is distorted.

So far, so good. I guess we can all agree with that.

It’s not time and distance that has changed. Time has not dilated. Our perceptions become distorted, and the math shows by how much.

That's apparently not what Special Relativity says of the twin paradox thought experiment: Send one twin for a trip of twenty years at 0.6c and he will come back four years younger than the twin that kept himself safe here on Earth. That's an actual difference, not just something that "appears distorted to the observer". Well, at least that's what Paul and Albert claimed.

A or B?

Or some C?
EB

 

[bigfield]

As I understand it, time isn't supposed to elapse for anything moving at speed c, and therefore, in particular, for photons. However, light is also supposed to be an electromagnetic wave, i.e. essentially a wave of orthogonal magnetic and electric magnitudes moving at c in a vacuum.

I'm not entirely sure how this is supposed to go, however.

As I see it, a wave is a propagation of a quantity in a medium, but an electromagnetic wave is a propagation in spacetime, which is supposed to be nothing else but all events considered collectively. The only things which seem changing in the case of light are the magnetic and electric magnitudes at the location the wave is moving across. However, there seems to be two possible scenarios...

One scenario, (A), is as follows. Let's assume that at a point x in space and just before the front of a light wave gets there at t0, the magnetic and electric magnitudes are zero or near zero. When the front of the wave gets to x, the magnetic and electric magnitudes will take one particular value each and those two values will no change as the wave moves across point x. I think that's called a stationary wave...

In a second scenario, (B), the wave is moving as a block so that the values of the magnetic and electric magnitudes at point x will keep changing according to which part of the wave is moving across this point.

It may be a bit complicated to understand like this, so a nice picture might help:

View attachment 20888​

So, in the case of light propagating "freely" through space, in a vacuum, which of the scenarios A and B is the correct one?

Or is it something else altogether?

Thanks,
EB

Photons aren't EM waves. That's mixing Electromagnetic Theory and Quantum Theory, which are different takes on electromagnetism.

In EM theory, light is an electromagnetic vibration that travels at c, and behaves more of less like drawing B shows. RF technology wouldn't work if it didn't.

In quantum theory, light is quantised and each photon consists of a "wave packets".

https://en.wikipedia.org/wiki/Wave_packet

These also propagate through space like drawing B, but it moves like a standing wave surrounding a moving point in space, which is different than the way a EM wave emanates from an RF transmitter.

Delta-t is only non-zero for a theoretical observer, such as the one at x. This is because Special Relativity (a different theory again) suggests that objects moving at c experiences no passage of time, which is a bit of a noodle-bender.

 

[steve_bank]

A or B?
Or some C?
EB

Y = A*sin(2PI*f*t) where f is frequency and t seconds. A is magnitude. Pick a frequency and a ste of points at time intervals and plot it by hand.

C is velocity.

That is all there is to it. Velocity - distance/time. You question is the same for a golfball in flight or or an EM wave.

Attach a rope to a wall and move one end up and down. If the rope is long enough you will see something like a sine wave on the rope. It is a transverse wave like EM waves. Amplitude varies orthogonal to line of propagation. Try that as a visualization to answer your question.

 

[Speakpigeon]

Thanks. B seems good to me.

OK for QM and Special Relativity being completely distinct perspectives, but I was really talking only of Special Relativity, though I didn't made that clear. Still, I expect both EM waves and photons together, right?
EB

 

[steve_bank]

It is easy to overthink the problem when trying to tie in trlstivity and QM.

In practical terms we only actually see macroscopic effects. Voltage, current and other things. A propagating wave is simple. Simple calculations. The intensity or power in the wave is reduced to photons when the wave interacts with a photo detector. A detector can be described by electrons per photon as a voltage or current.

At the practical level we try to stay macroscopic as much as possible.

Don't know if it is in print, there used to be a paperback All About Waves. Good read.

 

[fast]

That's apparently not what Special Relativity says of the twin paradox thought experiment: Send one twin for a trip of twenty years at 0.6c and he will come back four years younger than the twin that kept himself safe here on Earth. That's an actual difference, not just something that "appears distorted to the observer". Well, at least that's what Paul and Albert claimed.

If they truly believed that it would have actually been time that would change (and not keep a steady beat), the conjured up thought experiment helps explain the actual ramifications but only if what they believed is true. Our true age and signs of aging have not been put to scientific testing...just that clocks diverge.

 

[bigfield]

Thanks. B seems good to me.

OK for QM and Special Relativity being completely distinct perspectives, but I was really talking only of Special Relativity, though I didn't made that clear. Still, I expect both EM waves and photons together, right?
EB

Well, not really. Not in the same theory. They are two different ways of modelling electromagnetism.

Quantum field theory, specifically quantum electrodynamics, attempts to reconcile particle physics (like photons) with special relativity and EM theory. In QED, photons are still particles, and particles are considered to be excited states of fields. Photons are excited states of the EM field. But the field in QED doesn't have waves like the field in EM theory.

 

[steve_bank]

Is QED a working theory?

To the OP my point is that regardless of underlying theory we only have a limited number of ways to effect a measurement.

Regardless of the photons traveling in a wave resulting in an electric and magnetic field in the end we measure an amplitude in volts.

 

[bigfield]

Is QED a working theory?

Yes.

See here: https://en.wikipedia.org/wiki/Precision_tests_of_QED

 

[steve_bank]

Is QED a working theory?

Yes.

See here: https://en.wikipedia.org/wiki/Precision_tests_of_QED

Thanks. Are you inferring QED is a unified field theory?

Jump to search



Quantum electrodynamics (QED), a relativistic quantum field theory of electrodynamics, is among the most stringently tested theories in physics.

The most precise and specific tests of QED consist of measurements of the electromagnetic fine-structure constant, α, in various physical systems. Checking the consistency of such measurements tests the theory.

Tests of a theory are normally carried out by comparing experimental results to theoretical predictions. In QED, there is some subtlety in this comparison, because theoretical predictions require as input an extremely precise value of α, which can only be obtained from another precision QED experiment. Because of this, the comparisons between theory and experiment are usually quoted as independent determinations of α. QED is then confirmed to the extent that these measurements of α from different physical sources agree with each other.

The agreement found this way is to within ten parts in a billion (10−8), based on the comparison of the electron anomalous magnetic dipole moment and the Rydberg constant from atom recoil measurements as described below. This makes QED one of the most accurate physical theories constructed thus far.

Besides these independent measurements of the fine-structure constant, many other predictions of QED have been tested as well.

 

[bigfield]

Is QED a working theory?

Yes.

See here: https://en.wikipedia.org/wiki/Precision_tests_of_QED

Thanks. Are you inferring QED is a unified field theory?

No. It's only concerned with electromagnetism. A UFT would cover all of the fundamental interactions.

 

[Speakpigeon]

That's apparently not what Special Relativity says of the twin paradox thought experiment: Send one twin for a trip of twenty years at 0.6c and he will come back four years younger than the twin that kept himself safe here on Earth. That's an actual difference, not just something that "appears distorted to the observer". Well, at least that's what Paul and Albert claimed.

If they truly believed that it would have actually been time that would change (and not keep a steady beat),

As I understand it, time doesn't exist as such. Spacetime does. There are apparently different perspective on what is spacetime, but let's ignore those for now.
The consequence seems to be that things have paths in spacetime, and that two things, say twin A and twin B, coinciding twice, at some two distinct locations in spacetime, say L1 and L2, may in between those two locations come to follow distinct paths, with the result that the time components of their respective spacetime paths will end up being different. Assuming the two twins have the same age at L1, they may really no longer have the same age at L2. That's what I understand the theory implies at any rate.

the conjured up thought experiment helps explain the actual ramifications but only if what they believed is true.

Sure. But there are some observations that seem to confirm the veracity of the phenomenon, in particular particle decay where the observed lifetime of the particle depends on its velocity relative to the observer, and as predicted by special relativity.

Our true age and signs of aging have not been put to scientific testing...just that clocks diverge.

Sure, but if clocks diverge, I mean good German clocks, I would expect the body clock of two twins to tick-tack accordingly.
EB