Instantaneous Communications plus Time Dilation Equals ???

[Xavier Onassiss]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

If you'd read the linked Wiki article' date=' you'd see that we're not talking about Doppler shift in light.[/quote']

 

True, the wiki article doesn't discuss the frequency shift of the light, but yes, that's also another effect of relativity. As I understand it, the stationary observer would see the light on board the train 'blue shift' as it's approaching, and 'red shift' as it's receding. The observer on board the train, however, wouldn't observe this effect.

 

In answer to the question, how can the light do both? --it doesn't, actually, at least not both in the same reference frame. In different reference frames, measurements of the same light will give different results. Which one is considered 'real'? According to Einstein, both are equally vaild. What does this mean?

 

Suppose instead of a moving train car and a platform, you had two parallel tracks, each with an observer in a train car. You run the experiment with car A moving, and car B stationary, then run it with car A stationary and car B moving in the opposite direction. Using only the measurements of the lights aboard the cars, can you tell which car was moving and which was stationary in each trial? Good luck.

 

Don't look at me,

Xavier Onassiss

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

True' date=' the wiki article doesn't discuss the frequency shift of the light, but yes, that's also another effect of relativity. As I understand it, the stationary observer would see the light on board the train 'blue shift' as it's approaching, and 'red shift' as it's receding. The observer on board the train, however, wouldn't observe this effect.[/quote']

 

Unless I'm mistaken, the Doppler shift in light isn't an effect of relativity.

[IndianaJoe3]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

True, the wiki article doesn't discuss the frequency shift of the light, but yes, that's also another effect of relativity. As I understand it, the stationary observer would see the light on board the train 'blue shift' as it's approaching, and 'red shift' as it's receding. The observer on board the train, however, wouldn't observe this effect.

 

In answer to the question, how can the light do both? --it doesn't, actually, at least not both in the same reference frame. In different reference frames, measurements of the same light will give different results. Which one is considered 'real'? According to Einstein, both are equally vaild. What does this mean?

 

I'm not a physicist, but it seems that, "frequency" is a function of the observer, not of the light itself.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

BTW, I am sorry about getting worked up and derailing the thread. I'm going to have to do a lot of reading to reconcile that train example with an objective universe, I'm afraid. I am convined that the universe is objective, so everything, IMO, has to work from there.

[dmjalund]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

the universe is objective - but time (and the concept of now) isn't

[Xavier Onassiss]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Unless I'm mistaken' date=' the Doppler shift in light isn't an effect of relativity.[/quote']

 

At any speed high enough to cause a measurable doppler shift in light waves, special relativity is a factor. See this article for more details.

 

 

 

Don't look at me,

Xavier Onassiss

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

At any speed high enough to cause a measurable doppler shift in light waves' date=' special relativity is a factor. See this article for more details.

 

Which is coincidental, not causal, and not related to the effect being claimed in the "passing train" example.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

the universe is objective - but time (and the concept of now) isn't

 

Then the universe wouldn't be objective. You can't have it both ways.

[Xavier Onassiss]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Which is coincidental' date=' not causal, and not related to the effect being claimed in the "passing train" example.[/quote']

 

That's right, it's a different experiment. (And I never said otherwise.) However, it stands as a demonstration of relativity, as observers in different reference frames will see the same phenomenon in different ways. And both sets of measurements will be equally valid.

 

 

Don't look at me,

Xavier Onassiss

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

That's right' date=' it's a different experiment. (And I never said otherwise.) However, it stands as a demonstration of relativity, as observers in different reference frames will see the same phenomenon in different ways. And both sets of measurements will be equally valid.[/quote']

 

How is Doppler shift a demonstration of relativity? It's a demonstration that the wave (or wave-like phenomenon) appears compressed or stretched by the motion of the source and/or the "observer", not a demontration of Special or General Relativity. Not all things that are relative are part of Relativity.

[sinanju]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Then the universe wouldn't be objective. You can't have it both ways.

 

Well, actually, you can. The whole basis of Relativity is that the only constant is the speed of light. Everything else folows from that. Whether you're moving at a snail's pace or at .99C, you will still see light moving at lightspeed. Since the only way that can work mathematically is if the speed of passage of time changes with (meaningful) changes in your velocity, you get time dilation effects. And redshifts in light coming from distant galaxies that are moving away from us at large fractions of C.

 

Your intuitions about constancy (an "objective" universe) are based on a brain which evolved in a single frame of reference, where nothing ever moved at more than an incredibly tiny fraction of the speed of light, so relativity effects were negligible. Questions of simultaneity don't arise because everyone and everything on earth is in the same frame of reference. Newton's laws of gravity aren't exactly right, but they're close enough to right to be useful, just like our intuitions about simultaneity and the like are good enough for a single frame of reference. But when you start working with velocities and forces at the levels Relativity is concerned with...they're not.

 

However much it offends one's sense of reality, Relativity works. There are real-world, practical problems that can only be adequately addressed if Relativity is taken into effect (the timing of GPS satellite signals, for one). Even if Relativity is eventually superceded by another theory, that theory will have to explain everything Relativity explained, just like Relativity had to adequately cover Newtonian physics (and answered some of hte questions Newton's theory couldn't, like the known but inexplicable issues with Mercury's orbit around the sun).

 

The universe IS objective--but some of the standards we take for granted on a daily basis (simultaneity, constant rate of time, etc.) aren't, in fact, actually fixed. They can change, based on other criteria. (It's kind of like having a Platonic yardstick that is always exactly a yard long...unless forces beyond anything we could ever hope to apply are applied, in which case it will stretch or contract. For all practical purposes that yardstick is always exactly a yard long. Under the ight circumstances, however, it isn't.)

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Well, actually, you can. The whole basis of Relativity is that the only constant is the speed of light. Everything else folows from that. Whether you're moving at a snail's pace or at .99C, you will still see light moving at lightspeed. Since the only way that can work mathematically is if the speed of passage of time changes with (meaningful) changes in your velocity, you get time dilation effects. And redshifts in light coming from distant galaxies that are moving away from us at large fractions of C.

 

Your intuitions about constancy (an "objective" universe) are based on a brain which evolved in a single frame of reference, where nothing ever moved at more than an incredibly tiny fraction of the speed of light, so relativity effects were negligible. Questions of simultaneity don't arise because everyone and everything on earth is in the same frame of reference. Newton's laws of gravity aren't exactly right, but they're close enough to right to be useful, just like our intuitions about simultaneity and the like are good enough for a single frame of reference. But when you start working with velocities and forces at the levels Relativity is concerned with...they're not.

 

However much it offends one's sense of reality, Relativity works. There are real-world, practical problems that can only be adequately addressed if Relativity is taken into effect (the timing of GPS satellite signals, for one). Even if Relativity is eventually superceded by another theory, that theory will have to explain everything Relativity explained, just like Relativity had to adequately cover Newtonian physics (and answered some of hte questions Newton's theory couldn't, like the known but inexplicable issues with Mercury's orbit around the sun).

 

The universe IS objective--but some of the standards we take for granted on a daily basis (simultaneity, constant rate of time, etc.) aren't, in fact, actually fixed. They can change, based on other criteria. (It's kind of like having a Platonic yardstick that is always exactly a yard long...unless forces beyond anything we could ever hope to apply are applied, in which case it will stretch or contract. For all practical purposes that yardstick is always exactly a yard long. Under the ight circumstances, however, it isn't.)

 

Fine, fine. I'm not saying anything about the GPS signals or any other experiements. Obviously, there's a lot of confirmation there.

 

But the idea that the light in the train thought experiment can actually, physically strike the ends of the train car both simultaneously and at different times is nonsense.

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

But the idea that the light in the train thought experiment can actually, physically strike the ends of the train car both simultaneously and at different times is nonsense.

 

This is the root of the problem right here: you're assuming that "simultaneously" is an objective quality, based on your experience in a world where nothing is moving relative to anything else. The fact is, the intuition and common sense that you learned in this world are just not adequate to make predictions beyond the meter-scale, standard temperature and pressure, low-velocity world that humans evolved in.

 

The universe is not obligated to make sense within our limited experience.

 

You can find a good starting point on this subject Here.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

The question I'm asking has nothing to do with limited experience or brain evolution or common sense or intuition or anything of the sort.

 

Does the light, itself, physically hit the ends of the train car at the same time, or not? Pick one.

 

I'm not asking what someone on the platform would see, I'm not asking what someone on the train would see. I'm asking about what the light does.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Does the light' date=' itself, physically hit the ends of the train car at the same time, or not? Pick one.[/quote']

Is an electron a particle or a wave? Pick one.

 

Look, you are not going achieve understanding about the relativity of simultaneity on an RPG forum. If you are serious about figuring this out, you should go audit a college course on relatvity, or find a physics professor who is willing to sit down with you and go over things.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Is an electron a particle or a wave? Pick one.

 

An electron is an electron, as a photon is a photon.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

An electron is an electron' date=' as a photon is a photon.[/quote']

 

Ah, ah, ah, play fair please. That is not the question I asked.

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Does the light, itself, physically hit the ends of the train car at the same time, or not? Pick one.

 

It depends on how you're moving relative to the train; because "at the same time" is not absolute for events separated in space.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

It depends on how you're moving relative to the train; because "at the same time" is not absolute for events separated in space.

 

I'm not asking about someone moving along with the train.

 

I'm asking about the light.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Ah' date=' ah, ah, play fair please. That is not the question I asked.[/quote']

 

It's not a wave, and it's not a particle. It's an electron.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

It's not a wave' date=' and it's not a particle. It's an electron.[/quote']

 

OK, in that case, the light does not physically hit the end of the train car at the same time, and the light does physically hit the end of the train car at the same time. If you avoid my "pick one", then I have to avoid your "pick one."

 

The basic problem is: under the relativity of simultaneity, there is no such thing as "the same time." It does not exist, not in an absolute sense. So your question is unanswerable.

 

Like I said: find a professor of physics and ask them.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

So if an electron is neither a wave nor a particle, and that "avoids your question", you're saying that the light neither hits at the same time nor at different times?

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

So if an electron is neither a wave nor a particle' date=' and that "avoids your question", you're saying that the light neither hits at the same time nor at different times?[/quote']

Yes.

In the same sense, you are neither a male nor a female, you are a Kristopher.

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

The light hits the front of the train first.

The light hits the front of the train and the back of the train at the same time.

The light hits the back of the train first.

 

All of these are true; which version is true depends on the observer's motion relative to the train.

 

I really don't know how to put it more plainly than that.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

The light hits the front of the train first.

The light hits the front of the train and the back of the train at the same time.

The light hits the back of the train first.

 

All of these are true; which version is true depends on the observer's motion relative to the train.

 

I really don't know how to put it more plainly than that.

 

Yeah, I get what you're saying, I've gotten that all along.

 

What I've been saying is, how the hell?

 

The light appearing to do something different, I can accept. The light actually, physically doing all three and more? No, that's just goofy.

 

And I don't know how to put it more plainly than that.