My Problems With Relativity

[DaveTheJackal]

[OK I have to go now as guests are arriving so this may need some editing still. Hopefully it kinda makes sense]

A few of my problems with relativity, both of which might expose my extreme leymanish understanding of relativistic issues! Both problems are about the relatativistic effects of velocity.

I am sure we've all heard the example of time dilation due to velocity where a space ship heads away from the earth to alpha centuri at close to the speed of light and, due to its velocity, we'd see time slowing down due to relativity ...

My problem with that whole example is this:

To the people on the spaceship, they would be the stationary observers and the earth would be moving away relative to them at close to the speed of light and hence (surely) they'd see time slowing down for us.

a. Is this the case?

b. If so then how can the two simultaneously be true in any traditional layman's view of what time is?

c. When physicists say 'time slows down' for an object are they talking about the observed rate at which time passes for the object rather than whats actually happening to it? i.e. we see things happening more slowly on the object rather than them actually slowing down?

I assume all of the above would be true of the theoretical claim that an object 'travelling faster than the speed of light' would travel backwards through time.

Realtive to what? The earth I assume. Surely to any observer on the object would 'see' (for want of a better word) the earth relative to them moving faster and so perceive that moving backwards through time.

Is what the physicists are actually describing the fact that we would see what happened to the object in reverse order - i.e. we would see it moving backwards through time? This makes sense to me, for an object approaching the observer at least.

This would be my understanding of the situation, but I'd thought I'd ask for an expert opinion.

As far as I know although we have some physical evidence of relativity due to gravitation (flying clocks around the world etc) there's none for relativity due to velocity, other than that it correctly predicts what we as 'stationary' observers can expect to see (i.e. it correctly predicts what will be observe in certain situations NOT what is actually happening).

Essentially relativity seems to map the universe on to a space which describes what we observe, and thus the models are dictated by or choice of viewing media. We have the conceit of believing all there is to the universe is what we perceive ... and I have a real problem with this.

Imagine, if you will, a race that evolved to an enlightened state without knowledge of EM radiation, lets say in the dark seas of Europa.

Without light they no eyes, no perception of EM radiation at all all sensory input comes from sonar. They develop a perfectly good working model of their perceived universe, with relativity based around the speed of sound, perhaps a little earlier in their history than us, given that any perceived distortions due to velocity would exaggerated and more easily measured than those of light.

As a result, europan science correctly predicts that as the velocity of an object approaches the speed of sound the mass of the objects approach enourmous proportions (supersonic travel is well beyond the current capabilities of Europan science).

We, on the other hand, with our extra weapon of observation through light, would see no such thing. Europans science merely adds extra mass to the object so that, at the velocity they perceive it moving at (due to their choice of viewing medium) the object's mass etc fits their other perceived experimental data.

What their science predicts is what they will observe, not what is actually happening, and the same, I believe is the case with Relativity.

(Not a perfect analogy I know ... but you understand my my point I hope).

Surely a better approach for either science (human/europan) to take would be to understand the behaviour of their viewing media, take this in to account when making observations, but then, when they have their observations, do a little more work and create a model of the universe as it actually is.

At the very least physicists should be aware of what they're doing (i.e. predicting what might be observed) and stop disappearing up their navels, making idiotic predictions about the universe about such things as time travel!

Such an approach would certainly save a lot of red faces on both europa and planet earth... (Note: unable to perceive 'redness' as such, traditional Europan scientists would describe such a phenomena as 'time dilation due to embarrassment', the speed of sound accelerated by the warmed fluid around the cheeks *joke*).

Anyhoo comments/answers please. I may be completely wrong in my understanding of this whole field. As I have said I don't have an in depth knowledge of these issues!

[Exapno Mapcase]

Originally Posted by DaveTheJackal

To the people on the spaceship, they would be the stationary observers and the earth would be moving away relative to them at close to the speed of light and hence (surely) they'd see time slowing down for us.

a. Is this the case?

b. If so then how can the two simultaneously be true in any traditional layman's view of what time is?

c. When physicists say 'time slows down' for an object are they talking about the observed rate at which time passes for the object rather than whats actually happening to it? i.e. we see things happening more slowly on the object rather than them actually slowing down?

Let's concentrate on this for a moment rather than the rest of your post.

a. This is the case. Relativity theory says that time is meaningful to you only inside of the one particular reference frame you choose to measure from. But see below because this is only part of the answer.

b. Throw out the layman's view. That's the revolution of relativity.

c. Inside any particular reference frame time moves at exactly one second per second for you. This is still true if you're moving near the speed of light. You can only tell that something unusual has happened if you move outside of your reference frame and attempt to sync up your clock with a clock in a different frame.

The physics folk will be here in a second to tell you how important that is. Basically, it's the difference between the special theory of relativity and the general theory of relativity. We really want to apply the general theory here because it cuts out a lot of problems.

Say you're taking a trip to the star Lalande 21185, which has planets orbiting it and is only 8.23 light years away. You accelerate at 1 gravity, to make the calculations smoother, for half the distance and then decelerate at 1 gravity for the second half of the journey so you come to a dead halt at the star.

One gravity acceleration doesn't sound like much but it brings your speed up to 98% of the speed of light by the halfway point, so all the relativistic effects come into play.

Here's what you see onboard the ship. It takes you 2.2685 years to get you to the halfway point and another 2.2685 years to get you to Lalande 21185 for a total of 4.537 years. If you turned around and went home you would arrive there after another 4.537 years. Call it 9 years total.

On earth, however, they would have calculated your voyage this way. It takes you 4.9986 years to get to the halfway point and another 4.9986 to get to Leland 21185, and then the same time to return. Call it 20 years.

Now you get out of your ship and compare chronometers. Yours reads 9 years and you are 9 years older in every possible way. The people on earth say that 20 years have gone past and they are 20 years older in every way.

How do you reconcile these two viewpoints? You can't. There are no layman's terms to express this difference. It's purely a function of relativity. Time and space are part of the same whole. They are not constant. Speed is the only constant. The faster you speed, the more time and space must change to keep the equations straight.

The rest of your analogy doesn't work. Sound is not a universal constant. It has no effect on anything. The speed limit, capital C, the theoretical speed of light in a perfect vacuum, is a constant. That was Einstein's tremendous insight. Everything stems from that one fact. Everything is relative - except the theoretical speed limit. Time really is affected because of this.

Flying clocks around the world is exactly an example of this. So are the effects of speeding particles in an accelerator up to 99.99+% of the speed of light. The equations predict the outcomes perfectly. There can be no doubt about this.

And nothing can go faster than light. Forget trying to make any sense of faster than light travel. Although the equations permit it in theory there are so many obstacles to describing the effects that's it would hopelessly confuse any conversation.

[WoodenTaco]

Originally Posted by Exapno Mapcase

Here's what you see onboard the ship. It takes you 2.2685 years to get you to the halfway point and another 2.2685 years to get you to Lalande 21185 for a total of 4.537 years. If you turned around and went home you would arrive there after another 4.537 years. Call it 9 years total.

On earth, however, they would have calculated your voyage this way. It takes you 4.9986 years to get to the halfway point and another 4.9986 to get to Leland 21185, and then the same time to return. Call it 20 years.

Why does this discrepancy occur? I've never done much reading on the topic, but you seem to have an excellent grasp on it and write in an especially lucid style. I've always wondered about this basic part of the theory.

[Exapno Mapcase]

Originally Posted by WoodenTaco

Why does this discrepancy occur? I've never done much reading on the topic, but you seem to have an excellent grasp on it and write in an especially lucid style. I've always wondered about this basic part of the theory.

Ugh. That's a much harder bit to explain since it means envisioning space-time.

But the simplest way I can explain it, hopefully not too oversimplified, is to think of distances in space-time as including a spatial component and a time component. A trip at relativistic speeds covers a greater amount of space-time than does the corresponding trip at non-relativistic speeds. (Even if the other clock stays still, it moves through time so there is always a space-time distance.)

The equation for it spells it out:
ds²=c²dt² - dx² - dy² - dz².

ds is the space-time distance between two events, dt, dx, dy, and dx are the four dimensions of space and time that are traveled.

But because the traveling clock and the earth-bound clock wind up in the same spatial location, i.e, the ds is equal is both cases, something has to give. We know that the spatial distances are longer, so the time component must be shorter. You can think of it as time speeding up or as less time elapsing. As far as we can tell, time appears absolutely normal inside any reference frame, so the less time elapsing explanation works better.

This all comes from the notions that there are no absolute reference frames, that the one constant must be a limit on speed, and that both space and time are equivalent dimensions in a four-dimensional space-time. Time cannot be considered something separate outside of space. All stem from Einstein's totally counterintuitive inspiration.

Dave, if you're determined to reject the last one hundred years of science there's nothing anybody can do for you. You don't grasp even the basic notions of the physics involved, let alone how general relativity works. Your explanations are at the level of creationism, in that you throw out all theory and experimentation and decide to go with anything that feels right to you. If you want to do that and remain ignorant, fine, but please don't try to argue it in front of actual physicists like Chronos. It's just insulting to him, even though he will patiently try to educate you. I won't. Everything you say is just plain wrong. If you want to learn what is right, then people will spend all the time needed to help you. If not, don't blame anybody but yourself.

[DaveTheJackal]

Originally Posted by Exapno Mapcase

Dave, if you're determined to reject the last one hundred years of science there's nothing anybody can do for you...

I'm not at all rejecting the theory, it correctly predicts what you will see from any particular frame of reference and has been proven to do so, my argument is that it doesn't tell you much about what's actually going on.

Going back to your earlier example, with the starship that accelerates to 0.98c.

From the point of view of the astronaut at mid journey, the point of 0 acceleration, he is stationary and it is the earth that is moving away at 0.98c.

He can shine a torch in any direction and the light beams will shoot off relative to him at c. In fact if he shines his torch back at earth he'd observe the earth receding at 98% of the speed of the photons emitted by the torch.

Viewing the earth he'd correctly observe things going slow there, since, relative to him the earth is moving at 0.98c.

As a result, using relativistic predictions the astronaut would expect to see his clock ahead of those on earth upon his return (since the earth is moving a relativistic velocities).

Please note I am not saying that observations from either earth or the spaceship would disprove relativity. They'd back it up 100%.

The 'problem' (for me) comes when the spaceship returns to earth, the spacemen and earth observers once again share a common frame of reference - each expecting their clocks to be ahead of the others.

Am I missing the point .... does relativity have an explanation for this situation that i'm not aware of ...?

[cmyk]

Originally Posted by DaveTheJackal

He can shine a torch in any direction and the light beams will shoot off relative to him at c. In fact if he shines his torch back at earth he'd observe the earth receding at 98% of the speed of the photons emitted by the torch.

The 'problem' (for me) comes when the spaceship returns to earth, the spacemen and earth observers once again share a common frame of reference - each expecting their clocks to be ahead of the others.

Am I missing the point .... does relativity have an explanation for this situation that i'm not aware of ...?

I hope I'm understanding you right, but the whole key to special relativity is the idea that no matter how fast you are (or are not) accelerating, of you turned on a flashlight, it will always appear to you to be moving away from you at 100% the speed of light. Everything is relative to that. If you were traveling at 99% C (relative to the earth), and shone a flashlight out of your ship in ANY direction, it would STILL recede from you at 100% C. You might expect that if you shone the light in the direction of your movement (since you're going 99% C) that the light would appear to be moving away from you at 1% C. Nope. So there's the crux of the whole thing right there. It's still moving at C relative to you.

The point of science is to create a hypothesis. You make some observations and come up with a hypothesis that might explain what it is you're seeing. Now you need some evidence to test your hypothesis so that it may become a theory. So you create a way, an experiment, to test your ideas (which are likewise based on your keen observations). After you perform some experiments, you obtain data and hopefully are able to extract some evidence from this data. If it supports you hypothesis, GREAT! You now have a theory. Now you need other people to test your theory in their own way. The results you consider evidence for your theory HAVE to be reproducible by everyone else. There are no ifs, ands or buts about this. The more evidence that is accrued in this fashion supporting your theory, the harder it will be to refute. If you doubt relativity, you have to come up with observations that fit with the mountain of reproducible evidence that has been observed over the last 100+ years, develop your own hypothesis, and start experimenting. Otherwise.. you got nothing.

It might be time better spent to learn the theory (and physics in general) you're trying to refute (even if only in part), before you start hypothesizing. There are real-live physicists here that have extensive experience, training and understanding. Keep an open mind and learn from them.

[Exapno Mapcase]

Originally Posted by DaveTheJackal

He can shine a torch in any direction and the light beams will shoot off relative to him at c. In fact if he shines his torch back at earth he'd observe the earth receding at 98% of the speed of the photons emitted by the torch.

This is where you're going wrong.

First, he doesn't need to shine his torch at anything. We see galaxies moving away from us at 98% of the speed of light just fine from their own light. They look entirely normal. Why? Because time moves normally from them just as it does for us. It doesn't matter which reference frame we pick. We're moving away from them at the same rate. Doesn't matter, because there is no absolute frame of reference with which to compare both of them simultaneously. It's that impossibility of simultaneous reference that is, again, Einstein's insight.

But we cannot synchronize our clocks with them because they have never been in the same frame.

The astronaut who has been on earth cannot synchronize his clock with the earth clock while he is an accelerating frame of reference. He does have to wait until both clocks are in the same frame of reference. The earth has not been accelerating; only the astronaut has. They have been through two different space-time routes. General theory, not special theory. Once the astronaut gets back, it is then and only then possible to see the effects on his clock of his having taken a longer space-time route to get back to the same place, thus affecting his time.

So the theory doesn't tell you "what you will see from any particular frame of reference." It tells you what your clocks will read once they have been brought back to the same frame of reference. That's a totally different thing.

And if you want to be believed when you say "I'm not at all rejecting the theory" you've got to stop saying things like "Count me in as an anti revolutionary."

[DaveTheJackal]

Yadda yadda yadda.

a. No they haven;t been able to prove anything by flying clocks around the world, how could they? After all, regarding velocity, each clock would be stationary and every other clock moving relative to it would be expected to be slower through time, so (logically) each clock involved in the would be expected to be behind the others.... since it and only it would be stationary relative to the others.

Meh they've given some evidence for relativity due to gravitation (eg planes flying at different altitudes) but that's about it.

It's a scientific oxymoron. There is no (and i doubt there will be) any verifiable scientific proof of relativity due to velocity.

b. I'd rather keep the lay man's view and remind the physicist that their mathematical short hand of describing what they see on their instruments ain't necessarily what's happening.

The revolution your referring to runs under the slogan 'forget what's really happening let's concentrate on what we can observe and what's easy to formulate'. Einstein's 'revolution'. Easy equations do not make reality.

c. again you're not making sense - to me at least.

Whatever star system astronauts headed out to they'd perceive time slowed down on earth at the same rate as people on earth perceived time slowed for them.... since at any one point each would be traveling (relative to the other) just as close to the speed of light as the object of their attentions would observe them to be traveling at.

So if, at any point a return to earth as made, all clocks (barring natural phenomena) would synchronize.

Count me in as an anti revolutionary.

d. you've missed the point of the Europans completely, to them sound is a universal limit, i was trying to point out how conceited we are to think we've discovered the fastest thing in the universe by giving an example of a science as badly limited (though perhaps more obviously ... to us humans at least) as ours.

Anyways - you haven't dissuaded me from my convictions - much booze - need bed.

Originally Posted by Exapno Mapcase

Let's concentrate on this for a moment rather than the rest of your post.

a. This is the case. Relativity theory says that time is meaningful to you only inside of the one particular reference frame you choose to measure from. But see below because this is only part of the answer.

b. Throw out the layman's view. That's the revolution of relativity.

c. Inside any particular reference frame time moves at exactly one second per second for you. This is still true if you're moving near the speed of light. You can only tell that something unusual has happened if you move outside of your reference frame and attempt to sync up your clock with a clock in a different frame.

The physics folk will be here in a second to tell you how important that is. Basically, it's the difference between the special theory of relativity and the general theory of relativity. We really want to apply the general theory here because it cuts out a lot of problems.

Say you're taking a trip to the star Lalande 21185, which has planets orbiting it and is only 8.23 light years away. You accelerate at 1 gravity, to make the calculations smoother, for half the distance and then decelerate at 1 gravity for the second half of the journey so you come to a dead halt at the star.

One gravity acceleration doesn't sound like much but it brings your speed up to 98% of the speed of light by the halfway point, so all the relativistic effects come into play.

Here's what you see onboard the ship. It takes you 2.2685 years to get you to the halfway point and another 2.2685 years to get you to Lalande 21185 for a total of 4.537 years. If you turned around and went home you would arrive there after another 4.537 years. Call it 9 years total.

On earth, however, they would have calculated your voyage this way. It takes you 4.9986 years to get to the halfway point and another 4.9986 to get to Leland 21185, and then the same time to return. Call it 20 years.

Now you get out of your ship and compare chronometers. Yours reads 9 years and you are 9 years older in every possible way. The people on earth say that 20 years have gone past and they are 20 years older in every way.

How do you reconcile these two viewpoints? You can't. There are no layman's terms to express this difference. It's purely a function of relativity. Time and space are part of the same whole. They are not constant. Speed is the only constant. The faster you speed, the more time and space must change to keep the equations straight.

The rest of your analogy doesn't work. Sound is not a universal constant. It has no effect on anything. The speed limit, capital C, the theoretical speed of light in a perfect vacuum, is a constant. That was Einstein's tremendous insight. Everything stems from that one fact. Everything is relative - except the theoretical speed limit. Time really is affected because of this.

Flying clocks around the world is exactly an example of this. So are the effects of speeding particles in an accelerator up to 99.99+% of the speed of light. The equations predict the outcomes perfectly. There can be no doubt about this.

And nothing can go faster than light. Forget trying to make any sense of faster than light travel. Although the equations permit it in theory there are so many obstacles to describing the effects that's it would hopelessly confuse any conversation.

[Strinka]

Originally Posted by DaveTheJackal

I'd rather keep the lay man's view and remind the physicist that their mathematical short hand of describing what they see on their instruments ain't necessarily what's happening.

No offense, but a layman's understanding is not an understanding at all.

Here's the thing. The speed of light is constant in all inertial frames.
If I'm standing still, and you're running at 6 mph, and I throw a ball at 10 mph in the same direction you're running, it looks to you like the ball is moving only 4 mph.

But if you're running at half the speed of light, and I shine a flashlight, the beam of light is moving away from you at the speed of light. Not half the speed of light as you would intuitively expect. All of relativity is derived from that.

Oh, and the "clocks on airplanes" experiment does give evidence for time dilation by velocity. The planes have to start at rest, take off and accelerate while doing so. I don't know enough about how, but that makes a difference.

[cmyk]

Originally Posted by DaveTheJackal

d. you've missed the point of the Europans completely, to them sound is a universal limit, i was trying to point out how conceited we are to think we've discovered the fastest thing in the universe by giving an example of a science as badly limited (though perhaps more obviously ... to us humans at least) as ours.

Anyways - you haven't dissuaded me from my convictions - much booze - need bed.

I think you're dismissing Relativity too fast, before you truly grasp the idea here. And that's the hard part. It's counter-intuitive with our everyday speeds and experiences. Just like your hypothetical Europans, us humans have limitations. We are not arrogant and we realize this. We may be able to directly detect a VERY small part of the much broader EM spectrum, but we have no experience, and therefore have not evolved the necessary sensations to pick up on the outcomes of relativity. Why? Because we never even come close to relativistic speeds.

You're also making an obtuse assumption. Just because these Europans can't directly detect light (only sound), this means absolutely nothing. The speed of sound is not a universal constant. Please be clear on this: Light itself has nothing to do with C (the universal speed limit). It just happens that light is one of the very few things that can travel at that speed, because it is massless. We call it "The Speed of Light" only for convenience. We could just as well call it "The Speed of Gravity". The Europans surely have noticed gravity, haven't they?

[DaveTheJackal]

Other than the fact that in their neutral buoyancy environment makes gravity pretty much irrelevant for them, forget the Europans for now, they were meant to be an abstract (if imperfect) example of why modeling the universe based on your own personal frame of reference is not always a good idea... and the sort of nonsensical results/observations this can lead to.

[DanBlather]

This confused me as well for a long time. The answer is that for there can be a difference between the two frames of reference if one is accelerating. For example, a oerson in an elevator can feel the effects of acceleration at the begioning and end of their trip. That's how they can tell that they, and not the building are the one moving.

[DaveTheJackal]

Originally Posted by DanBlather

This confused me as well for a long time. The answer is that for there can be a difference between the two frames of reference if one is accelerating. For example, a oerson in an elevator can feel the effects of acceleration at the begioning and end of their trip. That's how they can tell that they, and not the building are the one moving.

That doesn't hold water surely and why in my previous example I deliberately used the example of the astronaut at the point of 0 acceleration.

Remember the earth is moving at one helluva rate to start with - relative to the 'centre' of the universe at least.

If the spaceship moves against the earths movement it's infact 'decelerating' for much of its journey.

Anyhoo such considerations are irrelevant as relativity (wisely) does away such fixed points of reference and correctly predicts what, from your own frame of reference, will be observed (as I have said before, this I do not dispute at all).

Whether it explains what is actually happening in the universe is another question!

[Napier]

1) You can be aware of time passing, and you can keep clocks of whatever accuracy you like, and rulers, and so forth. You will feel a force, a heaviness, a resting-against-something, when you are being accelerated, like in an elevator. You can feel the heaviness because you are close to a big mass, or because you are changing velocity; in fact at a fundamental level these two are actually identically the same thing. A key element of any relativity, the Einsteinian one included, is that all your experiences work out correctly and nothing ever appears wrong to you. Things only look weird when you compare notes with somebody else who has been moving differently than you have.

2) The velocity c is a deeply important thing. It is the speed of causes. It is the limiting speed at which any influence can spread. Light and other electromagnetic radiation and the radiation of gravitational field changes happen to propagate at this speed when nothing interferes with them, but c isn't something about light, it's something about cause and effect.

[SandyHook]

DaveTheJackal wrote:

Without light they no eyes, no perception of EM radiation at all all sensory input comes from sonar. They develop a perfectly good working model of their perceived universe, with relativity based around the speed of sound, perhaps a little earlier in their history than us, given that any perceived distortions due to velocity would exaggerated and more easily measured than those of light.


Having no eyes may not be the drawback you think. We can't directly perceive things like X-rays, cosmic rays, etc. We developed knowledge about them through indrect methods. For instance, infared was discovered (by Newton I think) while working with a prisim. In an attempt to determine the temperature associated with each color (or something like that) he discovered that the highest temp came in a zone next to red where there appeared to be nothing but, "normal" light.


As a result, europan science correctly predicts that as the velocity of an object approaches the speed of sound the mass of the objects approach enourmous proportions (supersonic travel is well beyond the current capabilities of Europan science).


You're also mistaken about the Europen science. Thier models would have fallen apart when actual measurements didn't show the expected change in mass. Regardless of what they thought or expected there would have to be some serious questions when the real world didn't fall into place.

[DaveTheJackal]

Originally Posted by SandyHook

Having no eyes may not be the drawback you think. We can't directly perceive things like X-rays, cosmic rays, etc. We developed knowledge about them through indrect methods. For instance, infared was discovered (by Newton I think) while working with a prisim. In an attempt to determine the temperature associated with each color (or something like that) he discovered that the highest temp came in a zone next to red where there appeared to be nothing but, "normal" light.

Perhaps i wasn't explicit enough. My basic premise was the Europans have no concept of EM radiation at all. The fastest (if not only) thing they know is sound.
Jeeze i deliberately didn't go in to the far reaches of the whole Europan confusion over heat radiation (they're essentially very very cold blooded so more heat to them means time passes faster. To them temperature and the rate as which time passes are the same thing (C) (TM). Ho hum so much for trying to keep things simple.

Originally Posted by SandyHook

DaveTheJackal wrote:

You're also mistaken about the Europen science. Thier models would have fallen apart when actual measurements didn't show the expected change in mass. Regardless of what they thought or expected there would have to be some serious questions when the real world didn't fall into place.

I didn't mention anything about europan science falling apart.

As far as I am concerned it would hold together.

For example... the first time a Europan was shot with an earthen (supersonic) rifle they'd see the bollet going backwards through time. Moving faster than sound the first thing the europan on the receiving end of the bullet would perceive is the impact of the bullet itself. The sound waves from its procession through the ocean would then hit, giving the europan the impression of something moving progressively further away from the point of impact (since the bullet would move ahead of the sound it created the bullet would hit befoe the sound in created say 1 second before impact) ... effectively moving backwards in time.

Put another way ... what does the europan percieve?
The bullet moves faster than the speed of sound.
First perception: the impact of the bullet.
1 sec later it perceives where the bullet was 1 second before impact (as the sound from that event reaches the Europan - ok maybe slightly more than 1 sec as the sound has to travel through the ocean).
2 secs later it perceives where the bullet was 2 seconds before impact (as the sound from that event reaches the Europan).... further away than where the bullet was 1 second before impact (less sound wave travel time).
3 seconds later it perceives where the bullet was 3 second before impact (as the sound from that event reaches the Europan)... further away than where the bullet was 2 seconds before impact (less sound wave travel time).
etc

Effectively the Europan perceives the bullet moving backwards through time, impact preceded by its position 1 second before impact ... then it's position 2 second before impact etc etc ... proving rather than disproving europan relativistic science the bullet is, using Europan relativism moving backwards through time.

That don't say that they're right about the physical nature of the universe though. They are describing what they would perceive rather than what's happening. Sadly, like most modern human scientists, the Europan physicists community have forgotten this is what their equations do.

Europan physics predicts that objects moving faster than the speed of sound are observed to move backwards through time ... and that's just what is observed. However, just like human physicists they've forgotten that what they observe isn't necessarily what's actually happened.

Europan science would not be right just because they could explain the whole shooting incident with their voodoo relativistic witch doctor theories, just like human relativistic physicists, by any common sense understanding they'd be talking nonsense - even if they'd predict what they'd observe correctly.

More examples and explanations later ... atm fighting off the effects of 2 bottles of wine wot ho! l8rs ;-)

[Bosda Di'Chi of Tricor]

DaveTheJackal--Welcome to the SDMB!

[Chronos]

b. If so then how can the two simultaneously be true in any traditional layman's view of what time is?

Define "simultaneously". Since time depends on your reference frame, two events which occur at the same time in one reference frame may well occur at different times in some other reference frame. The only situation where you can say that two events unambiguously occur at the same time is when they also occur at the same place. So if two space travellers meet up again and shake hands, they're going to have to be able to agree, then, on which one is older, but if they don't ever meet again, each one will say the other one is older.

As far as I know although we have some physical evidence of relativity due to gravitation (flying clocks around the world etc) there's none for relativity due to velocity, other than that it correctly predicts what we as 'stationary' observers can expect to see (i.e. it correctly predicts what will be observe in certain situations NOT what is actually happening).

We have a middling amount of experimental evidence of General Relativity (the relativistic theory of gravity) though not nearly as much as we'd like. But the evidence for Special Relativity (which deals with speeds) is absolutely astounding. Special relativity is the most thoroughly tested theory in all of physics, and possibly in all of science, and it has passed all of its tests with straight A+.

Imagine, if you will, a race that evolved to an enlightened state without knowledge of EM radiation, lets say in the dark seas of Europa.

Without light they no eyes, no perception of EM radiation at all all sensory input comes from sonar. They develop a perfectly good working model of their perceived universe, with relativity based around the speed of sound, perhaps a little earlier in their history than us, given that any perceived distortions due to velocity would exaggerated and more easily measured than those of light.

There's no reason that your hypothetical Europans would develop a theory of relativity based on sound, because the Universe doesn't work that way. Measurements of space and time are not affected by relative motions comparable to the speed of sound the way they are by the speed of light. It's not just that light happens to be the fastest thing we know of, it's that there's an inherent speed built into the fabric of the Universe, and light just happens to be one of a few things which travels at that speed. Relativity deals with the inherent speed built into the Universe, and works just as well even if there doesn't happen to be anything which moves at that speed.

[cmyk]

There is no center of the universe. This is why this is so confusing to you. You need a better understanding of some of the basics of physics and space-time before you can really grasp this subject, me thinks.

[DaveTheJackal]

Originally Posted by cmyk

There is no center of the universe....

Isn't that what I just said?

[cmyk]

Originally Posted by DaveTheJackal

Isn't that what I just said?

I quit.

[marshmallow]

The problem with your Europan analogy is that we aren't very different from them in the sense that we can only detect a small band of all possibilities using our evolved senses. We can only see light around the 400-700 nm range and we can't hear very high pitched or very low pitched sounds. We have no idea what it would be like to be an ant, who lives in a world of complex chemical signals from hundreds of invididuals in her immediate vicinity. Or a mole, who uses hyper sensitive tactile sensations to explore his world...

However, we are a technological race and can build machines that can detect such phenomena and translate it into a language we can understand. Presumably an intelligent, social, and technological echolocating race would as well. There's no reason they wouldn't know as much about EM radiation as we do.

[DaveTheJackal]

Originally Posted by mstay

The problem with your Europan analogy is that we aren't very different from them in the sense that we can only detect a small band of all possibilities using our evolved senses. We can only see light around the 400-700 nm range and we can't hear very high pitched or very low pitched sounds. We have no idea what it would be like to be an ant, who lives in a world of complex chemical signals from hundreds of invididuals in her immediate vicinity. Or a mole, who uses hyper sensitive tactile sensations to explore his world...

However, we are a technological race and can build machines that can detect such phenomena and translate it into a language we can understand. Presumably an intelligent, social, and technological echolocating race would as well. There's no reason they wouldn't know as much about EM radiation as we do.

The Europans - they were an abstract example. Yes I know they would probably have discovered EM radiation were they real - i was postulating an artificially created race who could perceive the world only through sound to illustrate my point.

... in the same way physicists use the idea of 2 dimensional species (also extremely unlikely to exist) to explain such issues as the curvature of space and extra dimensions in space time.

[DaveTheJackal]

Originally Posted by cmyk

I quit.

"Anyhoo such considerations are irrelevant as relativity (wisely) does away such fixed points of reference and correctly predicts what, from your own frame of reference, will be observed (as I have said before, this I do not dispute at all)."

Was it really that hard to understand?

[cmyk]

Originally Posted by DaveTheJackal

Surely a better approach for either science (human/europan) to take would be to understand the behaviour of their viewing media, take this in to account when making observations, but then, when they have their observations, do a little more work and create a model of the universe as it actually is.

At the very least physicists should be aware of what they're doing (i.e. predicting what might be observed) and stop disappearing up their navels, making idiotic predictions about the universe about such things as time travel!

Such an approach would certainly save a lot of red faces on both europa and planet earth.

It's assumptions like these that make me roll my eyes. How stupid do you think scientists are? Everything imaginable is taken into consideration, especially the idea that we might not be able to detect something directly. It's almost what science is all about. Reverse engineering the universe, so to speak. This is also what makes science hard... especially when the results of such don't meet intuitive expectations (and then explain this to the laymen). Sound familiar?

[DaveTheJackal]

Originally Posted by cmyk

It's assumptions like these that make me roll my eyes. How stupid do you think scientists are? Everything imaginable is taken into consideration, especially the idea that we might not be able to detect something directly. It's almost what science is all about. Reverse engineering the universe, so to speak. This is also what makes science hard... especially when the results of such don't meet intuitive expectations (and then explain this to the laymen). Sound familiar?

About as stupid as the idea of a 2-d race living on a balloon...

They're called 'thought experiments', abstract examples to illustrate points.

Anyways back to my original question. Let me break it down:

The first part:

Since the spaceman perceives himself at rest would he observe time slowing down on earth, since, relative to him, the earth is moving at 0.98c?

[cmyk]

Originally Posted by DaveTheJackal

About as stupid as the idea of a 2-d race living on a balloon...

They're called 'thought experiments', abstract examples to illustrate points.

Anyways back to my original question. Let me break it down:

The first part:

Since the spaceman perceives himself at rest would he observe time slowing down on earth, since, relative to him, the earth is moving at 0.98c?

Huh? That comment was in response to the idea that scientists don't take anything but their own evolved senses into consideration. Which is utter nonsense. The thought experiment of the Europans I was not knocking in any way (no matter how flawed it actually is). You were making a direct and insulting criticism of science in general, and I was merely pointing out how invalid and silly it was.

Thought experiments I regard when they are accurate and actually expose a truth. Einstein had a lot of these... look into them.

[DaveTheJackal]

Originally Posted by cmyk

Einstein had a lot of these...

One of these being the use of sound to illustrate the behavior of light at relativistic speeds as I remember. Adds a bit of gravitas to my example I guess.

[phaemon]

The "who ages faster/slower" question is sometimes referred to as "The Twin Paraxdox". There's an explanation of how it works here.

Originally Posted by DaveTheJackal

There is no (and i doubt there will be) any verifiable scientific proof of relativity due to velocity

Yes, there is. There are multiple experiments that confirmed the predictions. The effects are taken into account every day for adjusting your GPS.

[DaveTheJackal]

Originally Posted by phaemon

The "who ages faster/slower" question is sometimes referred to as "The Twin Paraxdox". There's an explanation of how it works here.

Yes, there is. There are multiple experiments that confirmed the predictions. The effects are taken into account every day for adjusting your GPS.

Again you're missing my point. Relativity accurately predicts the behaviour of light and allows for corrections in the received signal I don't refute this.

[phaemon]

Originally Posted by DaveTheJackal

Again you're missing my point. Relativity accurately predicts the behaviour of light and allows for corrections in the received signal I don't refute this.

What? The first link explains what you clearly don't understand about how the time dilation effect works.

The second tells of all the effects that have to be taken into account to keep GPS accurate, including dilation. Would you prefer I linked to another experiment instead? Try these.

[DaveTheJackal]

Originally Posted by phaemon

What? The first link explains what you clearly don't understand about how the time dilation effect works.

The second tells of all the effects that have to be taken into account to keep GPS accurate, including dilation. Would you prefer I linked to another experiment instead? Try these.

Yes, relativity does explain what you can expect to observe from a certain frame of reference.

Now please, someone answer my original question:

Since the spaceman moving at constant velocity perceives himself to be at rest, would he observe time slowing down on earth, since, relative to him, the earth is moving at 0.98c?

[Senegoid]

Originally Posted by phaemon

The "who ages faster/slower" question is sometimes referred to as "The Twin Paraxdox". There's an explanation of how it works here.

Before I even read any more in this thread, I must reply: Phaemon, thank you relatively massively very much for this link. This particular question in particular, standing out amidst Mr. Jackal's commentary, is one that I have long wondered about, in my non-technical lay ignorance. (And yes, I did note your correction to the link in the following post.) I never heard of the paradox under the term "Twin Paradox" before. I just took at a quick glance there, and I've bookmarked it for a more thorough perusal at my leisure. I am gathering that the non-intuitive asymmetry in their aging profiles is due to the fact that, for all their relative relativity, the fact is that one is accelerating WRT the other and can detect that, while the other (on earth) sees himself as "stationary" with the other (in the ship) as accelerating, and can detect that. This, after all the math is done, leads to the asymmetry in their aging when they finally meet again? Have I got at least this much right?

[phaemon]

Oops, wrong page for the Twin Paradox, just click "Top" on that page.

[cmyk]

Didn't seem to sink in, though.

You do realize there's a fundamental difference between how sound and light works, right? Sound cannot travel at C, light can. And you can catch up to sound wave (sonic boom), you cannot with light.

[DaveTheJackal]

Originally Posted by cmyk

Didn't seem to sink in, though.

You do realize there's a fundamental difference between how sound and light works, right? Sound cannot travel at C, light can. And you can catch up to sound wave (sonic boom), you cannot with light.

Since the spaceman moving at constant velocity perceives himself to be at rest, would he observe time slowing down on earth, since, relative to him, the earth is moving at 0.98c?

[snailboy]

I have a question on this topic. General relativity says that acceleration and gravity are the same, but when it says gravity, is it referring to freefalling (actual acceleration although you can't feel it) or standing on the surface of a planet (not accelerating but feels like it)?

[cmyk]

Originally Posted by snailboy

I have a question on this topic. General relativity says that acceleration and gravity are the same, but when it says gravity, is it referring to freefalling (actual acceleration although you can't feel it) or standing on the surface of a planet (not accelerating but feels like it)?

IANAPhysicist, but as I understand it, if it FEELS like acceleration, then it's acceleration or gravity. You have to be in the right context to understand where it's coming from. So, If you were in a box that completely shut out the world, you wouldn't be able to tell the difference between the pull of earth on your body, or if you were away from any gravitational influence, yet accelerating at 1G. Same inertia... same feeling.

If you are falling... this is no different than if you were standing firmly on the ground. The earth ALWAYS has this pull on you... this acceleration. As far as you're concerned, it could be that you're in zero G, floating peacefully, as the earth is rushing toward you at 120 mph. The difference being, is that earth will try and accelerate your body up to 120 mph in a split second (when you hit ground). That hurts. It's better to never have jumped from that plane to begin with... as before you left the ground, you were already "traveling" at 120 mph with the earth. That's why parachutes are important... they decelerate you (or the earth, depending on how you look at it) slow enough where your body can handle it.

One minor detail: the earth has an atmosphere, which introduces "terminal velocity". This is the point where the friction of the air, counteracts the acceleration of gravity. If the earth had no air... then you'd just keep accelerating faster and faster until you hit pay-dirt. No ~120 mph speed limit.

Also, I suppose then, the effects of earth's gravitational pull on you, could be lessened or increased if you were able to accelerate the earth as well. But once you reached a constant speed/velocity, everything will feel like it's not moving again. Just be sure to brace yourself. (as I am now doing for anything I may have gotten wrong here)

[tomh4040]

May I assure you all that if anything travels faster than light, it does not travel in time, and nor does anything else. Causality is not violated, it just appears to be so to a particular observer. If I set off in my fast jet, break the sound barrier, and land (all in a straight line), I can then listen to myself arriving. I have not arrived before I set off. Likewise, if I fly my spaceship faster than light, and then come to a stop (in a straight line), I can see myself arriving. I have not arrived before I set off.
I think we can all agree that two clocks which are experiencing 1G run at the same rate, and therefore stay in sync. This is still true if one is experiencing 1G because it is on the surface of the Earth, and the other is undergoing an acceleration of 1G. Einstein’s equivalence principle and the experiment with the man in the chest :- “Relativity The Special And The General Theory”, Methuen and Co 1920, chapter XX .

I set off in my spaceship to Alpha Centauri with the rocket accelerating at 1G. At the half way point it turns round and decelerates at 1G. It comes to a stop at AC, and without cutting the motor, is immediately accelerated back towards Earth at 1G, again turning and decelerating at the half way point, coming to a halt at Earth. The total journey time was 7.8 years, and the total distance covered was 8.8 light years. The clocks on the spaceship were always subject to 1G as were those on Earth, therefore keeping in sync with each other. I certainly did not arrive at AC before I set off, and did not arrive back at Earth before I set off.
The above scenario is allowed. As the rocket and the rocket motor are in the same reference frame (FR), there is no mass increase between the two, and I can use the Lorentz transformations to show this.
Remember that the v in these equations refers to the velocity of the rocket relative to a different FR, which the observer is in (and by inference the propulsion force : the only experiments which have been done to show mass increase with velocity have been under those circumstances). The applicable equation is m = m0 / sqrt (1-(v/c) ^2 ). Because v = 0 (the motor is in the same FR as the rocket, so there is no relative velocity), v/c = 0, and (v/c) ^2 = 0. The square root of 1 - (v/c) ^2 = 1, and m = m0 / 1. Therefore m = m0. As the acceleration is held to 1G for a distance of 2.2 light years before turning round to decelerate, the space ship will reach a speed greater than that of light (the velocity in meters per second at turn around will be 63.87 X 10e7 [ c = 30 X 10e7] ), and time on this space ship will pass at exactly the same rate as back at home on earth.

I urge you to look up :- http://myweb.tiscali.co.uk/carmam/Hollings.html by Tom Hollings
And :- http://www.aquestionoftime.com/ by Hans Zweig

[The Hamster King]

tomh4040, do you agree that light travels at the same speed in every reference frame? If not, how you do explain the Michelson-Morley experiment?

[ZenBeam]

Originally Posted by tomh4040

I think we can all agree that two clocks which are experiencing 1G run at the same rate, and therefore stay in sync.

I don't agree.

ETA: And of course, anything you derive by assuming this is suspect as well.

[Keeve]

Originally Posted by tomh4040

If I set off in my fast jet, break the sound barrier, and land (all in a straight line), I can then listen to myself arriving. I have not arrived before I set off. Likewise, if I fly my spaceship faster than light, and then come to a stop (in a straight line), I can see myself arriving. I have not arrived before I set off.

The two cases are significantly different in the eyes of mainstream science, which holds that nothing can go faster than light. Thus, according to mainstream science, the first case is quite possible, and the second is quite impossible, and therefore nothing can be proven or even demonstrated simply by waving your hand and asserting:

Originally Posted by tomh4040

May I assure you all that if anything travels faster than light, it does not travel in time, and nor does anything else. Causality is not violated, it just appears to be so to a particular observer.

You're gonna need more evidence than you've shown so far.

[Keeve]

Originally Posted by tomh4040

I think we can all agree that two clocks which are experiencing 1G run at the same rate, and therefore stay in sync. This is still true if one is experiencing 1G because it is on the surface of the Earth, and the other is undergoing an acceleration of 1G. Einstein’s equivalence principle and the experiment with the man in the chest :- “Relativity The Special And The General Theory”, Methuen and Co 1920, chapter XX.

Nope. It only works if the 1G is in the same frame of reference, as was Einstein's example, where they were both on Earth. But if we are in free fall above the Earth, or in free fall above the Moon, or in free fall above Pluto, all will experience the same 0G, but because of the difference frames of reference, which are traveling at different velocities, mainstream science says that they will be experiencing time at slightly different rates, and the clocks will NOT be in sync.

[tomh4040]

Originally Posted by Keeve

Nope. It only works if the 1G is in the same frame of reference, as was Einstein's example, where they were both on Earth. But if we are in free fall above the Earth, or in free fall above the Moon, or in free fall above Pluto, all will experience the same 0G, but because of the difference frames of reference, which are traveling at different velocities, mainstream science says that they will be experiencing time at slightly different rates, and the clocks will NOT be in sync.

Einstein's example was not based solely on the Earth. The man in the room was on the surface of the Earth, but the man in the chest was being accelerated "by a hyothetical being pulling on a rope...". Also, before the experiment starts, Einstein places the man in the chest "...in a large portion of empty space..." and says "Gravity naturally does not exist for this observer." If we are to believe Einstein that gravity and acceleration are indistinguishable, then the clocks must run at the same rate, or they would not be indistinguishable. I totally agree with Keeve that in freefall, or under any acceleration other than 1G, the clocks will not stay in sync, but these 2 clocks are both in 1G, and therefore will stay in sync. Keeve's argument ( and any argument along the same lines) is therefore flawed.

I am of course aware that mainstream science says that nothing can travel faster than c, and I covered that with the Lorentz equations concerning mass increase. Perhaps I did not go into enough detail, but paragraph 3 covers it as far as I can see. Maybe I was being a bit theatrical in the opening sentence, for that I apologise.

If anyone disagrees that 2 clock both under 1G will not run at the same rate, would you please explain why.

[Frylock]

Originally Posted by Dave

I'm not at all rejecting the theory, it correctly predicts what you will see from any particular frame of reference and has been proven to do so, my argument is that it doesn't tell you much about what's actually going on.

What does "what's actually going on" mean and why are you saying physics ought to be telling us about it?

[northdakotatroy]

I didn't read all the responses to this question, so I apologize if I'm repeating.

Time travels slower for those on the ship. If we could observe them from Earth, they would appear to be moving in slow motion.

However, traveling faster than the speed of light is impossible no matter the size and power of the ship because relativity states the faster you travel, the ships mass increases exponentially. So the faster you go, the heavier the ship is, the more power required, increasing the necessary fuel load which makes the ship heavier, requiring more power to go faster, and on and on...

An interesting side note: according to Stephen Hawking, time travel to the past is impossible, but time travel to the future can be done... On a ship traveling at 99% of the speed of light, each day that passes equates to one year on Earth. So if you could travel at 99% of the speed of light for one year, you would return to Earth 365 years in the future.

But you can't go back.

[zombywoof]

Originally Posted by northdakotatroy

An interesting side note: according to Stephen Hawking, time travel to the past is impossible, but time travel to the future can be done...

I think you'll find those principles were worked out (without benefit of time travel) some decades before Stephen Hawking was born.

[northdakotatroy]

Originally Posted by zombywoof

I think you'll find those principles were worked out (without benefit of time travel) some decades before Stephen Hawking was born.

I'm quite aware of that, but I was referring to a specific speech I heard Stephen Hawking give, so I credited him. Is that OK with you?

[tomh4040]

Originally Posted by northdakotatroy

I didn't read all the responses to this question, so I apologize if I'm repeating.

However, traveling faster than the speed of light is impossible no matter the size and power of the ship because relativity states the faster you travel, the ships mass increases exponentially. So the faster you go, the heavier the ship is, the more power required, increasing the necessary fuel load which makes the ship heavier, requiring more power to go faster, and on and on...

I'm not going anywhere while you are all still talking about me.
The above point is easy to refute. It is on my web site and on this forum in a very early posting of mine (if not the first).

The applicable equation is :- m = m0 / sqrt(1 - (v/c)^2) .

m = mass of body under discussion
m0 = rest mass of same body
v = velocity (but see below)
we all know c

All experiments which have been done to "prove" mass increase, have used an external power source ie a particle accelerator. The PA and the particle itself consist of two seperate FRs, and the power source is electro magnetic. The PA is pushing (from eg FR1) the particle (in eg FR2) using a force which is itself constrained to c, so cannot possible push anything faster than that speed, hence the illusion of mass increase.
Contrast that scenario with this one. The rocket motor is in the rocket, therefore in the same FR as the rocket. The v in the above equation is the relative velocity between the rocket and its power source (the rocket motor). The relative velocity between motor and rocket is zero. Make v = 0 in the above equation and you will see that m = m0. There is no mass increase.

[northdakotatroy]

Originally Posted by tomh4040

I'm not going anywhere while you are all still talking about me.
The above point is easy to refute. It is on my web site and on this forum in a very early posting of mine (if not the first).

The applicable equation is :- m = m0 / sqrt(1 - (v/c)^2) .

m = mass of body under discussion
m0 = rest mass of same body
v = velocity (but see below)
we all know c

All experiments which have been done to "prove" mass increase, have used an external power source ie a particle accelerator. The PA and the particle itself consist of two seperate FRs, and the power source is electro magnetic. The PA is pushing (from eg FR1) the particle (in eg FR2) using a force which is itself constrained to c, so cannot possible push anything faster than that speed, hence the illusion of mass increase.
Contrast that scenario with this one. The rocket motor is in the rocket, therefore in the same FR as the rocket. The v in the above equation is the relative velocity between the rocket and its power source (the rocket motor). The relative velocity between motor and rocket is zero. Make v = 0 in the above equation and you will see that m = m0. There is no mass increase.

Well it looks like you've suceeded at disproving one of the most tested theories in the history of science.

Can we expect a paper to be published in a peer-reviewed scientific journal of some kind soon?