Time Halt and Speed of Light

[Tom Mattson]

Solid reasoning, folks.

 

If you can do better, then I'm all ears. So far all you've done is present arguments of incredulity, based on false statements made about relativity. Surely you don't expect anyone to be convinced by that.

[swansont]

Nevermind. I'm wrong, and you are all correct. When something travels FTL wrt something else, it's time and length both become imaginary. Of course it makes no physical sense, but that's just the way it is becuase the SR equations say so. And, since SR was apparently constructed to deal with every possible speed, all numbers (useful or otherwise) produced by an equation with a defined upper limit for real answers[/b'] should also simply be accepted. Beyond that, we should accept that reality will follow that equation into the imagination of the mathematician. Solid reasoning, folks.

 

You keep hammering on this point and it's wrong. c isn't a defined upper limit. That's the conclusion that is drawn, because the terms in the SR equations are meaningful only if they are real and nonnegative. You can have equations where negative or imaginary terms have physical meaning, it's just that this isn't one of those cases.

 

And I agree with what Tom said in the last post. Feel free to build a better mousetrap, but don't expect science to discard a process that works just because it doesn't give you a warm fuzzy feeling.

[Mowgli]

Space and time are modes by which we think, not conditions in which we live. It is not easy to think of time in moving coordinate systems, because motion mixes space and time. The best model we have so far to handle it is SR, which does not apply to FTL travel. So don't ask questions about the nature of time for FTL travel and expect sensible answers

 

SR has been around for about 100 years, may be we will have a better model soon...

[Saint]

You keep hammering on this point and it's wrong. c isn't a defined upper limit. That's the conclusion that is drawn, because the terms in the SR equations are meaningful only if they are real and nonnegative. You can have equations where negative or imaginary terms have physical meaning, it's just that this isn't one of those cases.

 

you paraphrased (although you highlighted it correctly)- I said it was the defined upper limit for real answers. If you input a FTL speed, you get an imaginary number. That is, non-real. So c is the upper bound for real answers.

 

 

And I agree with what Tom said in the last post. Feel free to build a better mousetrap, but don't expect science to discard a process that works just because it doesn't give you a warm fuzzy feeling.

 

As I said, this post isn't about bashing relativity. It's about the misuse, in my opinion, of relativistic equations. That's all.

 

And, I'm not trying to build a better mousetrap here. I'm trying to tell people not to misuse the one they have. It's a mousetrap, not a catch-all.

[Saint]

No' date=' Saint, SR was designed to answer the question, "What type of universe is it that has the same speed of light for all inertial observers, and the same laws of physics for all inertial observers." As long as those two things hold true, then we are in the domain of applicability of SR.

[/quote']

 

So you believe that the speed of light is held contant for an inertial observer travelling FTL? Or, you believe that the laws of physics are the same for an inertial observer whose time and length are both imaginary?

 

I don't know how you can make that claim when no one seems to have a physical correlation to imaginary length and time. The laws of physics are still based in a physical reality. Can you show me how the same laws of physics apply to an inertial frame with imaginary space and time? And, if you can, how do you come by the knowledge of how imaginary space and time behave? What assumptions do you have to make?

[swansont]

you paraphrased (although you highlighted it correctly)- I said it was the defined upper limit for real answers. If you input a FTL speed' date=' you get an imaginary number. That is, non-real. So c is the upper bound for real answers.

 

(...)

 

As I said, this post isn't about bashing relativity. It's about the misuse, in my opinion, of relativistic equations. That's all.

 

And, I'm not trying to build a better mousetrap here. I'm trying to tell people not to misuse the one they have. It's a mousetrap, not a catch-all.[/quote']

 

The equations give an imaginary answer for v>c. How is that a misuse of relativistic equations?

[Tom Mattson]

So you believe that the speed of light is held contant for an inertial observer travelling FTL? Or' date=' you believe that the laws of physics are the same for an inertial observer whose time and length are both imaginary?

[/quote']

 

No, I believe that observers can't travel FTL.

[rajama]

I know when something is accelerated it will be moving slower.

and I know when something is going faster than the speed of light - in theory - time would go backwards.

 

Common misconception. Time would not go backwards at FTL speeds' date=' it would become imaginary (a product of the square root of -1) [/quote']

 

Doesn't this misconception stem from the thought experiment where two light signals (say A & B) are intercepted by two observers having a relative speed greater than c and one sees A then B & the other B then A..?

[parkinho]

'two observers having a relative speed greater than c'

 

but this cannot happen. Or have I misunderstood the point that you were making?

[rajama]

Oh, I was thinking of lines drawn on a 'light cone' type diagram...

 

You know - where the horizontal axis is a space dimension and the vertical axis is time, and light moves at 45 degrees?

 

Your sub-c observer is a line sloping more than 45 degrees (timelike), the super-c less than 45 degrees (spacelike). Then, if you also have two 45 degree lines (light signals) crossing the paths of the two observers, they cross in opposite order..? They can't agree in which order the signals arrived..?

[timo]

'two observers having a relative speed greater than c'

 

but this cannot happen. Or have I misunderstood the point that you were making?

While I didn´t understand rajama´s post, I think I can help you out here:

Two particles can have a relative velocity greater than c. If one particle travels to the left with 3/4c and the othe one to the right with 3/4c, then they do have a relative velocity of 6/4c = 1.5c > c. That´s not forbidden by relativity as both have a velocity of < c (for the nitpickers I´d like to explicitely exclude non-observable and non-observed particles here).

 

However: In contrast to nonrelativistic physics and intuition the relative velocity of two particles does not remain the same when switching to a different frame of reference. In fact, the relative velocity will change in such a way that the relative velocity of the particles will allways be <= c in a frame in which one of the particles is at rest. If it wasn´t like that the other particle would have to have a velocity > c which isn´t possible since a velocity <= c in any coordiante system will be <= c in any other (the number which describes whether a particle travels with lightspeed, slower than c or >c is the same in any coordiante system).

 

To sum it up: Relative velocities >c are possible if none of the particles / observes is at rest in the frame of reference the relative velocity is measured in but relative velocity is frame-dependent.

 

Oh, and: Every particle that travels with <c is a valid observer.

[parkinho]

Yeah, cheers. I had my wires crossed/not thinking properly.

[Mowgli]

Two particles can have a relative velocity greater than c. If one particle travels to the left with 3/4c and the othe one to the right with 3/4c, then they do have a relative velocity of 6/4c = 1.5c > c. That´s not forbidden by relativity as both have a velocity of < c.

Hmmm.... this seems to imply that the light emitted by the particle going left will never reach the particle going right, in my frame of reference.

In fact, the relative velocity will change in such a way that the relative velocity of the particles will allways be <= c in a frame in which one of the particles is at rest.

This implies that the light from the first particle will always reach the other particle, in the frame of reference of the first particle. Now, reality cannot change (at least, I don't think it can ) just because we change frames of reference. Genuine paradox or pure ignorance on my part?

[Janus]

Hmmm.... this seems to imply that the light emitted by the particle going left will never reach the particle going right' date=' in my frame of reference.

 

[/quote'] No, because light travels at c relative to you in your frame. Therefore it will catch the particle going to the right at 3/4c.

This implies that the light from the first particle will always reach the other particle, in the frame of reference of the first particle. Now, reality cannot change (at least, I don't think it can ) just because we change frames of reference. Genuine paradox or pure ignorance on my part?

 

Yes it does reach the other particle in this frame, just as it does in every frame.

[greentea]

Maybe Syd's comment is actually quite relevant since it illustrates another model, namely v=s/t, which yields a different result. Still, we 'know' (punctuation intentional, please do not go into semantics) that relativity is a better model in this case. Whether it gives meaningful results for speeds above that of light is purely a speculation in my opinion (and a nice thread topic, I guess).

[Tom Mattson]

v=s/t is not another model. In fact it isn't a model at all and it doesn't give results of any kind. It's a definition. It holds true in Galilean Relativity, Special Relativity, or General Relativity.

[iglak]

But you'll really have a few choices:

 

1) stop

2) faster

3) reverse

 

reverse doesn't exist in the real world.

speed and length can't be negative.

 

 

imagine a line on a linear graph, with one endpoint centered at 0, and the other endpoint free to move negative and positive on the graph.

at point 5, the line is 5 units long.

at point 2, the line is 2 units long.

at point -2, the line is 2 units long.

at point 0, the line is non-existant.

you could say that point -2 is positive in the negative direction, and thus the measurement is negative, but that's false outside of mathematics. in the real world, you can simply flip the measurement system around, and create a different reference point to make the line positive length in the positive direction again. negative doesn't existant in real measurements.

there is no negative direction in reality, only different directions.

 

speed acts the same. the speed of a vehicle can't ever be negative.

the speed of time, as a number (with an imaginary unit), can be thought of as the length of the line.

it can increase and decrease, but it can't go negative. there is, again, no negative direction for the speed of time to be measured. only positive.

 

also, notice that a value of 0 causes the measurement to be nonexistant. if an object has a size of 0, it can't be sensed or measured, and thus doesn't exist. if an object moves at 0 velocity, it's not moving. in real measurements, there is no such thing as moving at 0 velocity, only an absence of movement.

 

similarly, if the speed of time were to become 0, time would no longer exist. that can't happen, because time does exist.

the speed of time can, however, get infinitely close to 0, and be observed as not moving.

 

 

but that doesn't cover imaginary. imaginary does, in fact, exist in the theoretical real world.

 

that line from the above thought experiment can go imaginary. in that case, it would no longer appear on the graph, but could still be measured on an imaginary graph.

 

it is thought, by some, that imaginary objects appear the same as real objects, but are inverted (or maybe everted) on a level that can't be seen. one possible way of visualizing this is anti-matter. i have no idea if anti-matter is or isn't imaginary matter, but the visualization could help anyway. to my knowledge (which is very limited on the subject), anti-matter and objects made of anti-matter look the same as matter and objects made of matter.

[Nicholas]

Time never stops.

 

Where time slows in gravity light also slows. They go hand in hand.

So time for light is distorted only by gravity and not its motion.

[Luminous]

light particles are always going the speed of light, so shouldnt time be stoped right now? or going backwards?

[swansont]

light particles are always going the speed of light, so shouldnt time be stoped right now? or going backwards?

 

You aren't a light particle, and can't be in a frame where a photon would be at rest. So the answer is no.

[LCD]

I don't think time stops, but our ability to observe it through reflected photons would be greatly altered.

 

In the direction of our travel vector the light we are using to measure time, movement, etc. would be caught at the back end, so to speak, and we'd be seeing light that already passed. The light parallel to us or behind us would not be able to keep up and would appear to fall away, or rather wouldn't reach our eyes, thus it would go dark.

 

the atomic clock would keep on keeping on though.... so time didn't stop, or reverse, only our ability to observe it would.

[brokenbin]

whatever divides by zero gives infinite.