Thread: Time Travel?

Sure you are.

In terms of what's traveling quicker, a rocket moving one third the speed of light obviously has a different relationship to the laser pulse I've shot into space than a more stationary object, such as a Xei whale floating in outer space. None of the objects the emitted laser light happens to encounter alter the constant speed at which it is traveling from its laser beam source.

I don't get why you don't just give the figures... I have a feeling from what you're saying that you have an incorrect absolute model of space and time, but I can't work it out because you won't answer the questions.

It's very simple... you're sat on the ground, and from your perspective, light is moving up and away from you at speed c, whilst the rocket is moving up and away from you at speed c/3. The questions are simple; from your perspective, how fast is the light moving away from the rocket, and then from the rocket's perspective, how fast is the light moving away (from the rocket)?

The answer to the latter half is 199,861,639 m/s.

I'm basically utterly unfamiliar with any maths and physics, so I'm not sure how to answer the first bit. Since there are three points of reference, aren't we missing a variable here? Maybe my own speed or the distance the rocket is from me? *embarrassed*

Don't forget you guys have forgotten that our planet is travelling at its orbital speed of 60,000 miles per hour and depending on where your laser is you have to take this speed into account too.

I was actually thinking about that, too, but didn't want to butcher the seemingly simple questions.

If you're totally unfamiliar, you should probably think in terms of distances in a set time. So, if light is moving at 300 million meters per second, that means in the first second it will have travelled 300 million meters. The rocket on the other hand will only have travelled 100 million. Therefore the light has moved away 200 million meters from the rocket in that second, so it is moving away from the rocket at 200 million meters per second.

Or you can think of vehicles on the road. If somebody is driving at 30 mph, and somebody behind them is driving at 10 mph, then the car in front is moving away from the car behind at 20 mph.

Anyway, the point is that you have an incorrect idea of space and time works. It is often misunderstood what 'the speed of light is a constant' actually means. What it means is that irrespective of its source, and irrespective of how fast you (or another object) is moving, the light will always move relative to you (or the object) at 300 million meters per second.

This means we have to come up with a totally different model of space and time. In the question I asked, the point is that although for you sat on Earth the light is moving away from the rocket at 200 million meters per second, for the rocket, the light is moving away at 300 million meters per second, whereas in our standard model of space and time it should still be 200 million.

If somebody fired a light beam towards you, if you tried to run away, it will still get 300 million meters closer to you every second, no matter how fast you ran. Or even if you ran towards it, the light wouldn't move towards you at a greater speed; it would still be coming towards you at 300 million meters per second.

Originally Posted by mcwillis

Don't forget you guys have forgotten that our planet is travelling at its orbital speed of 60,000 miles per hour and depending on where your laser is you have to take this speed into account too.

It's just an example. Disregard how fast the Earth is moving, it's minuscule compared to the speed of light anyway.

Its an interesting conundrum isn't it Xei

Originally Posted by Xei

irrespective of its source, and irrespective of how fast you (or another object) is moving, the light will always move relative to you (or the object) at 300 million meters per second.

Alright, I agree with your point that, relative to absolutely anything, a speed of 300 million m/s must always be attributed to light; that it is a property of light. However,

Originally Posted by Xei

This means we have to come up with a totally different model of space and time. In the question I asked, the point is that although for you sat on Earth the light is moving away from the rocket at 200 million meters per second, for the rocket, the light is moving away at 300 million meters per second, whereas in our standard model of space and time it should still be 200 million.

whether or not I am here to observe the light moving away from the rocket, the rate at which the light surpasses the rocket through space is 200 million m/s greater than that of the rocket. This is not subjective to an outside observer, nor is it denying how the light is still traveling at 300 million m/s. So, in regards to your example:

Originally Posted by Xei

If somebody fired a light beam towards you, if you tried to run away, it will still get 300 million meters closer to you every second, no matter how fast you ran.

although this is true, it is theoretically still possible for me to travel further and further away from the light as long as I'm traveling faster than it.

Originally Posted by Izrail

whether or not I am here to observe the light moving away from the rocket, the rate at which the light surpasses the rocket through space is 200 million m/s greater than that of the rocket. This is not subjective to an outside observer, nor is it denying how the light is still traveling at 300 million m/s.

It is subjective. If you were sat on the rocket, light would be moving away from the rocket at 300 M m/s. If you are stood on the Earth, the light moves away from the rocket at 200 M m/s.

although this is true, it is theoretically still possible for me to travel further and further away from the light as long as I'm traveling faster than it.

It is completely impossible. It makes no sense to travel faster than light, because the light will always be moving towards you at 300 million metres per second. It's catching up to you at a constant rate, and this means you're going slower than it.

Originally Posted by Xei

It is subjective. If you were sat on the rocket, light would be moving away from the rocket at 300 M m/s. If you are stood on the Earth, the light moves away from the rocket at 200 M m/s.

Well, no. As you said, the light is always moving at 300 M m/s. If light forever and always travels at a speed of 300 M m/s, it is an absolute, objective property of light. So, yes, that particular beam is moving at 300 M m/s, regardless the rocket is traveling at 100 M m/s. However, even if I am down here on earth smoking my pipe and observing the laser beam is traveling 200 M m/s faster than the rocket, I am simply observing two different (and hypothetically constant) rates of speed. If the beam was moving 300 M m/s away from point of view of the rocket, that would suggest the light is actually traveling at 400 M m/s.

Originally Posted by Xei

It is completely impossible. It makes no sense to travel faster than light, because the light will always be moving towards you at 300 million metres per second. It's catching up to you at a constant rate, and this means you're going slower than it.

If I have a massive, constant rate of speed as well, nothing is "catching up" to me.

Originally Posted by Izrail

Well, no. As you said, the light is always moving at 300 M m/s. If light forever and always travels at a speed of 300 M m/s, it is an absolute, objective property of light. So, yes, that particular beam is moving at 300 M m/s, regardless the rocket is traveling at 100 M m/s. However, even if I am down here on earth smoking my pipe and observing the laser beam is traveling 200 M m/s faster than the rocket, I am simply observing two different (and hypothetically constant) rates of speed. If the beam was moving 300 M m/s away from point of view of the rocket, that would suggest the light is actually traveling at 400 M m/s.

This is exactly the point. It doesn't suggest it. In the familiar model of space and time, yes, it causes a contradiction. What Einstein did was come up with a different model of space and time in which there is no contradiction.

For any object on Earth, the light is moving away from the rocket at 200 M m/s. For any object around the rocket, the light is moving away from the rocket at 300 M m/s.

Relative speeds of objects can change according to where you are.

This is extremely counter intuitive because on human scales, the effect is not noticeable. Nevertheless, it is true. It was discovered experimentally at the end of the 1800s.

If I have a massive, constant rate of speed as well, nothing is "catching up" to me.

Again this is the whole point. The light isn't just passively moving through some volume of space at 300 M m/s. It is moving towards you at 300 M m/s. No matter what you do, no matter how fast you go, it will still be moving towards you at 300 M m/s. There is no way to avoid the fact that it will catch up with you.

Are you trying to tell me that from aboard a capsule pod floating in outer space a good distance from Earth, I would witness the rocket to have a speed of 0 m/s within the exact moment it passed by me, allowing for the rate at which the light traveled away from the rocket to be 300 M m/s instead of 200 M m/s?

No, it doesn't make any sense for the rocket to not be moving as it moves past you. But if your capsule were moving alongside the rocket, you would see the light flying away from the rocket at 300 M m/s. If the capsule then stopped and the rocket kept flying away at 100 M m/s, you would then see that the light was flying away from the rocket at 200 M m/s.

Let's replace light with you and rocket with me. Let's have a race. The gun sounds, and you're off, whizzing at 300 M m/s while I hobble behind at 100 M m/s. 10 seconds later, I limp unto an accelerator pack that increases my speed by 200 M m/s. Is it feasible that your distance from me will stay the same once I activate the pack?

...

After laying down for a moment, I think I just grasped it. Movement is only a potential attribute of the rocket; it is not an intrinsic property. Yes, it has potential to fly at 100 M m/s. When it does, the exampled light beam is still traveling 300 M m/s; the rocket just happens to be traveling 100 M m/s toward it.

Light doesn't have potential to travel at 300 M m/s. Either it is illuminating and traveling at that speed, or there is no light. Thus, light can only be observed moving at any other speed. This is relativity. (Let me know if I'm wrong.)

It's not really about potentials. It simply is what it is. If there measuring device (your eye, for instance, or electronic recording devices, or whatever) on Earth, it will record that the light is getting 200M meters further away from the rocket every second. This is literally the reality of the situation. If the measuring device is moving with the rocket, it will record that the light is getting 300M meters further away from the rocket every second. This is also just as correct.

Time and space (and therefore velocities) simply work this way. There is no explaining why, it's just how the universe works. Light being constant means that for stuff moving quickly, space and time don't behave as we normally expect them to.

Originally Posted by Xei

If the measuring device is moving with the rocket, it will record that the light is getting 300M meters further away from the rocket every second. This is also just as correct.

Light being constant means that for stuff moving quickly, space and time don't behave as we normally expect them to.

This did it. Good show.

Originally Posted by Xei

There is no explaining why

as of yet, of course.

Originally Posted by Wayfaerer

as of yet, of course.

There will never truly be an explanation of anything without simply relying on some axiomatic observations. The constancy of the speed of light (or statements equivalent to it) is probably such a thing.

Originally Posted by Xei

There will never truly be an explanation of anything without simply relying on some axiomatic observations.

What do you mean by that exactly? The point of science is to explain axiomatic observations in increasingly unifiying models.

Originally Posted by Xei

The constancy of the speed of light (or statements equivalent to it) is probably such a thing.

I just can't help but think that the relations between light, space and time hide more profound connections.

Originally Posted by Xei

It is completely impossible. It makes no sense to travel faster than light, because the light will always be moving towards you at 300 million metres per second. It's catching up to you at a constant rate, and this means you're going slower than it.

Unless your local spacetime is undergoing a metric expansion. Unlikely, I suppose.

Originally Posted by Wayfaerer

What do you mean by that exactly? The point of science is to explain axiomatic observations in increasingly unifiying models.

Not really. The 'point' of science, or at least a very large part of it, and really all of theoretical physics, is to find an increasingly general set of axioms for observed phenomena, the ultimate goal of course being a single exhaustive set. But there will always be a set of axioms, and inherently, these cannot be explained. All reductionism ever does is reduces the number of axioms; it can't eradicate them, so that isn't really the goal. The idea that we'll ever be able to 'explain' reality as such is, unfortunately, mistaken.

Originally Posted by Xei

Not really. The 'point' of science, or at least a very large part of it, and really all of theoretical physics, is to find an increasingly general set of axioms for observed phenomena.

How is that different from what I said?

Originally Posted by Xei

But there will always be a set of axioms, and inherently, these cannot be explained. All reductionism ever does is reduces the number of axioms; it can't eradicate them, so that isn't really the goal. The idea that we'll ever be able to 'explain' reality as such is, unfortunately, mistaken.

That's why I said increasingly unifying, as in explaining long standing axioms with new ones that are simpler and more encompassing, knowing that the process might always continue. I just highly doubt we're anywhere near a supposed absolute axiomatic end concerning the speed of light or anything else really.

What you said suggested to me that you could 'explain axioms' in terms of something which wasn't axiomatic; I see that you meant the same thing.

I'm not sure about the constancy of the speed of light; it's so fundamental and atomic that it seems dubious to me that we'll ever explain it. Any mathematical theory of everything would necessarily encompass it, but it's not clear to what extent you can call that an 'explanation'. A bit like how you can formulate the natural numbers in terms of set theory, yet it's very dubious that that actually means anything.

I guess I just share a less dubious attitude toward fundamantal axioms being seen in new lights with new explainations. I suppose it just seems unlikely to me that history won't repeat itself in that way yet again.