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Author Topic: Physics/Theory of Relativity questions  (Read 4029 times)

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Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #25 on: June 15, 2012, 05:00:05 AM »
Ok, here's one that I've been curious about for a while. I get the whole space/time thing in that the faster something moves the slower time goes... and the whole idea of wormholes. My question comes into the spot right here... if someone made a wormhole pair, sent one out on a ship (wormhole X) at ~speed of light then return so that for the one that traveled (wormhole X), only a few hours passed while on Earth (wormhole Z) several years passed... so, in essence, we'd be able to travel between two times using those wormholes, right?

So, if that is true, then while X is in transit, and we were able to look through those wormholes and see the other side just fine, what does physics say we'd see from Earth? Does it say that we'd see the traveling side in real time to us or would it be slowed down to the point where it appears frozen? The way I am seeing it in my head, we'd have to see the other side in real time for the time travel to be possible.

Personally, I don't see time travel being possible. It makes the universe feel like a very messy place and all I've read and heard of physics at all levels, if something is messy, it is usually wrong. I know, couch-potato physics ideas like my own are usually missing some big peaces of the puzzle.

Now, for it to feel more... 'pretty?'... not right word, but at almost 5am, it will do... in my head, I can see the universe having time as a constant. Just hear me out a bit before pointing out that I am wrong and experiments have proven such. Time being a constant in that we can't escape the 'now'. Everything, be it billions of light years away or in the next room, all happens 'now'. However, that doesn't restrict us from perceiving or moving through now at a faster or slower rate.

Lets go back to those wormholes and see if I can't try and explain myself a little better by using examples.

As X moves near the speed of light, instead of it moving through time faster, it is actually still in the 'now', just moving really really slowly through 'now'. The same time dilation effects would still be seen and when returned to Earth, the same time differences would be seen, except that both wormholes would still be in the 'now'. There wouldn't be any time travel. While in transit, if we looked into Z to see what was happening on X, what we would see would be a very nearly frozen in time place as it traveled through 'now' at a very slow rate of speed even though it was traveling at a very high rate of speed through space.

I am just not sure if there are proven meth equations that show one way or the other, or even what kind of experiments could be had which would say one way or the other. Again, I've read a few books on this (they made my brain implode) and have watched many videos (Ted.com is awesome) but I've not found any that have really said anything that the way I'm seeing things is backwards. Again, in my head, it all works out well enough that it doesn't conflict with any theory that I know about.

Ideas anyone or did I just lose everyone with my random 5am ramblings... thanks ahead of time.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #26 on: June 15, 2012, 01:42:41 PM »
Ok, here's one that I've been curious about for a while. I get the whole space/time thing in that the faster something moves the slower time goes... and the whole idea of wormholes. My question comes into the spot right here... if someone made a wormhole pair, sent one out on a ship (wormhole X) at ~speed of light then return so that for the one that traveled (wormhole X), only a few hours passed while on Earth (wormhole Z) several years passed... so, in essence, we'd be able to travel between two times using those wormholes, right?

By just using Relativity, yes.

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So, if that is true, then while X is in transit, and we were able to look through those wormholes and see the other side just fine, what does physics say we'd see from Earth? Does it say that we'd see the traveling side in real time to us or would it be slowed down to the point where it appears frozen? The way I am seeing it in my head, we'd have to see the other side in real time for the time travel to be possible.

Remove the wormhole from the equation for a moment - it isn't necessary.

Someone is moving at .86 of c away from you. This gives a nice time dilation factor of 2.

8 seconds passes for you, you see that 4 seconds has passed for them. Likewise, 8 seconds passes for them, they see that 4 seconds has passed for you. These are both perfectly accurate statements about the Universe, but for as long as you are moving apart at .86 of c, you will each see each other as experiencing time at half of the 'proper' rate.

This is where time travel rears its ugly head - both of your frames of reference are perfectly legitimate. So if you have some sort of ansible to communicate with, you send a message at t=8, the target gets it at t=4, and you get the reply at t=2...

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Personally, I don't see time travel being possible. It makes the universe feel like a very messy place and all I've read and heard of physics at all levels, if something is messy, it is usually wrong. I know, couch-potato physics ideas like my own are usually missing some big peaces of the puzzle.

Meaningful FTL, Relativity, Causality, pick two. There are some very limited exceptions - you can use wormholes whose faces are fixed with respect to each other, for example (trying to do the typical ansible trick will cause the face of the wormhole to be deformed from your perspective, thus preserving causality), but otherwise, if meaningful FTL is possible in a universe that still maintains causality despite it, then something must be wrong with Relativity.

Note that what's wrong can certainly still permit our current understanding of Relativity - a preferred frame of reference that exists outside of our Universe is not observable, and thus, Relativity still holds for our 'limited' purview but there would be a point at which a new theory had to accommodate observations that occurred if/when some observable FTL phenomenon was discovered.

Note that there are faster-than-light phenomenon within our universe - matter falling into a black hole and the expansion of space - but these things are hidden from observers because they represent spacetime being deformed at such speeds.

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Now, for it to feel more... 'pretty?'... not right word, but at almost 5am, it will do... in my head, I can see the universe having time as a constant. Just hear me out a bit before pointing out that I am wrong and experiments have proven such. Time being a constant in that we can't escape the 'now'. Everything, be it billions of light years away or in the next room, all happens 'now'. However, that doesn't restrict us from perceiving or moving through now at a faster or slower rate.

The first thing anyone should study when looking into Relativity is the concept of frames of reference. Your idea of 'now', no matter how constant you think it is, is still a part of that frame.

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Lets go back to those wormholes and see if I can't try and explain myself a little better by using examples.

As X moves near the speed of light, instead of it moving through time faster, it is actually still in the 'now', just moving really really slowly through 'now'.

But Earth seems to be moving really slowly, from the perspective of the people on the other end of the wormhole. It isn't until they bring themselves back into Earth's frame (or at least close enough) that there can be any agreement. If Earth started zipping off after them at the same speed after several years, it would be the Earthlings who had very little time pass.

A 'true now' still represents a preferred frame - and is still verboten by Relativity. No concept of such that exists within our Universe is permissible by our observations.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #27 on: June 15, 2012, 04:15:00 PM »
By just using Relativity, yes.

Remove the wormhole from the equation for a moment - it isn't necessary.

Someone is moving at .86 of c away from you. This gives a nice time dilation factor of 2.

8 seconds passes for you, you see that 4 seconds has passed for them. Likewise, 8 seconds passes for them, they see that 4 seconds has passed for you. These are both perfectly accurate statements about the Universe, but for as long as you are moving apart at .86 of c, you will each see each other as experiencing time at half of the 'proper' rate.

This is where time travel rears its ugly head - both of your frames of reference are perfectly legitimate. So if you have some sort of ansible to communicate with, you send a message at t=8, the target gets it at t=4, and you get the reply at t=2...

Meaningful FTL, Relativity, Causality, pick two. There are some very limited exceptions - you can use wormholes whose faces are fixed with respect to each other, for example (trying to do the typical ansible trick will cause the face of the wormhole to be deformed from your perspective, thus preserving causality), but otherwise, if meaningful FTL is possible in a universe that still maintains causality despite it, then something must be wrong with Relativity.

Yeah, figured there was a lot I wasn't catching. Didn't think that wormholes fell into that 'FLT' category. I always thought of it as a ... non-travel? You enter one point, come out the other having gone a great distance but actually never did any traveling due to those two points being the same point, but at two different location.




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But Earth seems to be moving really slowly, from the perspective of the people on the other end of the wormhole. It isn't until they bring themselves back into Earth's frame (or at least close enough) that there can be any agreement. If Earth started zipping off after them at the same speed after several years, it would be the Earthlings who had very little time pass.

This one is hard for me to wrap my mind around. So, being on the ship, traveling at near the speed of light, everyone looking out would see everything going real slow, the same as anyone looking into the ship? I can't understand how that would happen, because as they slowed down, there would be at some point where everything would have to either jump or move way faster than the time differences should be for it to all come back into proper perspective.

(I know these aren't the actual correct time differences, but using them as a rough example)

From Earth, they are gone 100 years, on the ship they are only gone a few days. From either perspective time is moving really slow? At least that's how you made it sound from that part I quoted of what you said.

Offline AndyZTopic starter

Re: Physics/Theory of Relativity questions
« Reply #28 on: June 15, 2012, 05:04:29 PM »
Try wrapping your mind around it this way, AriDarrow:

No matter how fast they're going, no matter how much time dilates, light always appears to be travelling at c.

Whether the person is standing still or moving parallel to a laser beam, that laser beam appears to be travelling at the same speed.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #29 on: June 15, 2012, 06:26:35 PM »
Yeah, figured there was a lot I wasn't catching. Didn't think that wormholes fell into that 'FLT' category. I always thought of it as a ... non-travel? You enter one point, come out the other having gone a great distance but actually never did any traveling due to those two points being the same point, but at two different location.

The definition of FTL, for practical purposes, is that information moves between two points faster than a photon can. So yes, wormholes are generally regarded as an FTL mechanism.

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This one is hard for me to wrap my mind around. So, being on the ship, traveling at near the speed of light, everyone looking out would see everything going real slow, the same as anyone looking into the ship? I can't understand how that would happen, because as they slowed down, there would be at some point where everything would have to either jump or move way faster than the time differences should be for it to all come back into proper perspective.

Yes.

If it helps, picture, instead of Earth and a spaceship, just two spaceships in an endless void.

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(I know these aren't the actual correct time differences, but using them as a rough example)

From Earth, they are gone 100 years, on the ship they are only gone a few days. From either perspective time is moving really slow? At least that's how you made it sound from that part I quoted of what you said.

They look back on Earth after those days, they've only seen a few moments pass on Earth.

And this is why talking about wormholes tends to cause headaches with causality. Whose frame of reference is the correct one? Relativity says both, but if you want to maintain causality, you need to say 'neither'. Earth's can't be valid, else we could play this trick out over gigaparsecs and end up with even more ludicrous results.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #30 on: June 16, 2012, 02:17:39 AM »
Ah, I see where we are differing. If I am understanding you right, you are talking about looking at the Earth from the ship, that would cause the differences in what is seen with the flow of time. That's not what I am talking about though, my question lies in what is seen through the wormhole.

From what I understand of some views of a wormhole, they are in effect opposite sides of a 2 dimensional point in space, enter one side, come out the other, no space traveled even though the two sides could be light years apart.

If what would be seen from the ship looking back at Earth would be the same as what would be seen through the wormholes, then wouldn't that show time travel by such a method to be impossible and lean credence to the idea that time, or the 'now' that we are in, is 'static'? That's not a good way of phrasing it... but the time of night isn't letting my mind think of a better way.

The reason I ask that it not mattering if we view from the ship back to Earth or view through the wormhole, that what is seen would be the same is due to pretty much every scientist that I've seen talk about wormholes say it'd be otherwise due to that being the strongest possibility for time travel.

I do hope I was able to make my question a bit more clear on this and you see what I am talking about better.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #31 on: June 16, 2012, 04:35:30 AM »
Ah, I see where we are differing. If I am understanding you right, you are talking about looking at the Earth from the ship, that would cause the differences in what is seen with the flow of time. That's not what I am talking about though, my question lies in what is seen through the wormhole.

I am answering what is seen through the wormhole.

You fly away at .9999... of c (whatever level of Lorentz contraction you need for that), you see Earth through the wormhole as if the planet was nearly standing still, the light so redshifted you need to do hour-long exposures in pure darkness to know what's going on at the other end. A few days pass for you, you know you've moved 100 light-years from Earth's perspective... but Earth looks like mere seconds have passed. You bring yourself to a stop, and you and Earth both agree on the rate of time progression, but the Earth in the wormhole is still a century into the past from where someone on Earth looking into the now-non-redshifted wormhole is.


Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #32 on: June 16, 2012, 12:33:59 PM »
I really am trying to wrap my mind around this, and I think I see what you are saying. Just trying to picture it in my head on how it works. Never been one for trying to use the lingo of a field of study to try and explain it to someone who isn't a student of that field.

I just hitting a wall as to seeing how it would actually make a difference to a wormhole. I can see everything else just fine, but to me that one thing just throws it for a loop. As I said, the idea of time travel just seems to make everything feel messy but the rest of physics, even quantum physics, is very eloquent and beautiful.

Being that it is a 2 dimensional surface, so there being no space between the two sides, it puzzles me why having one side traveling at near the speed of light or sitting right next to it, would make any difference to the flow of time that you could see from the other side. As you are saying, it's is relative, so two rockets, each traveling at half the speed of light in opposite directions from each other, you look from one to the other, you see the other as if it were traveling at the speed of light away.

So, you look through the wormhole, and see an image that isn't moving any faster in relation to what you are, but the other side is actually traveling at great speeds away. Why would what you see through the wormhole be the same kind of image that you would see from the ship looking back? That's the part I am not grasping. You mention red-shift, c, Lorentz contraction... etc... those words have no meaning to me due to, as I said, not having taken any official studies in the field. Is there a way that you can put it, describe a scene, a story maybe, but without any of the jargon? Maybe that could help me wrap my mind around why the image you see through a wormhole, which seems like it wouldn't be traveling any speed in relation to it's other half, wouldn't differ from what could be seen from the ship itself back to the planet.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #33 on: June 16, 2012, 02:05:27 PM »
Well, it appears that I have managed to work my mind around the whole wormhole issue I was having. Don't really like the results that I can see though.

The ship relative to Earth, without the wormhole, time dilation takes effect, appears to slow down... etc. However, with the wormhole, in relation to the two sides, no traveling is taking place. Step through one side, you are on the other. What a person would see in looking in one side is real time on the other. So, time travel would be possible because the passage of time on the ship, say one year, would be what would be seen when the ship returns say 100 years later to Earth. So, in the past on Earth, a person would be looking 100 years into the future through the wormhole.

That is, if the actual results of said experiment would show the same results. Even today, experiments have shown that actual experiments of what was only theory give results different than what was expected, that is what I hope will result when this kind of a test is actually possible. As messy as I feel time travel make the universe, it may actually be a possible result.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #34 on: June 16, 2012, 02:29:41 PM »
The physical definition of travel is that information moves from point a to point b. Matter is a form of information.

If it's faster than a photon traveling the same route, it is, by definition, faster than light. Traveling is taking place, and your declaration that it isn't is physically nonsensical - information that was on Earth is now 100 light-years away, or vise-versa. That is travel. It violates the dominant energy condition by its very occurrence.



Your problem isn't that some sort of FTL travel is impossible while preserving causality. Your problem is in the assumption that Earth would be a preferred frame in such a scenario. This is the most common flaw of home-grown FTL constructs for science fiction. In order to have FTL and Causality, Relativity must, at some point, be wrong. Okay, this is fine - but it's certainly true for the Universe as we currently observe it, and, most critically, we observe no preferred frame, which is the simplest means by which FTL and causality can be permitted.

So that frame of reference, if it exists, cannot exist 'within' our universe. This means that your idea of a Universal 'now' can only, at best, be approximated (some researchers have posited that the IGM (Inter-galactic medium would best represent such a thing)... so can have your FTL and your Causality, but it means that certain things that people use in their descriptions of such things - like 'fifty times the speed of light' do not actually make sense. The speed of light remains a sort of infinite quantity, even in a universe where FTL and Causality still hold.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #35 on: June 16, 2012, 04:01:54 PM »
The physical definition of travel is that information moves from point a to point b. Matter is a form of information.

If it's faster than a photon traveling the same route, it is, by definition, faster than light. Traveling is taking place, and your declaration that it isn't is physically nonsensical - information that was on Earth is now 100 light-years away, or vise-versa. That is travel. It violates the dominant energy condition by its very occurrence.



Your problem isn't that some sort of FTL travel is impossible while preserving causality. Your problem is in the assumption that Earth would be a preferred frame in such a scenario. This is the most common flaw of home-grown FTL constructs for science fiction. In order to have FTL and Causality, Relativity must, at some point, be wrong. Okay, this is fine - but it's certainly true for the Universe as we currently observe it, and, most critically, we observe no preferred frame, which is the simplest means by which FTL and causality can be permitted.

So that frame of reference, if it exists, cannot exist 'within' our universe. This means that your idea of a Universal 'now' can only, at best, be approximated (some researchers have posited that the IGM (Inter-galactic medium would best represent such a thing)... so can have your FTL and your Causality, but it means that certain things that people use in their descriptions of such things - like 'fifty times the speed of light' do not actually make sense. The speed of light remains a sort of infinite quantity, even in a universe where FTL and Causality still hold.


Not sure I understood everything you were talking about there, again, using the terminology that I am not fully educated in is only adding to the confusion. The only reason I am using Earth instead of 2 ships or even 2 planets, is just one for convince. We live on Earth, and for the most part, it is the center of all that happens to us. Familiar starting point and something we can all feel safe using.

I understand that anything going over a distance is travel, but what distance is traveled between the wormhole sides? It's a 2 dimensional space, right? Someone walking at say, 2mph going into one side is walking the same 2mph coming out the other and if those ends of the wormhole are at opposite sides of the universe, does that mean that they have said ungodly high speed of some FTL travel, or were they only going at 2mph at all points?

It's well known that there are galaxies out there that are traveling away from us at speeds greater than the speed of light. It's not due to said galaxy actually traveling faster than the speed of light, but due to our mutual speeds traveling away from a random set neutral point between our two galaxies and the expansion of the universe. At no point is any going FTL, but combine all the factors and FTL is observed. I don't like saying it this way, but it's one of the better ways of putting, all speed is relative. Two ships traveling in the same direction next to each other at the speed of light, relative to each other neither is traveling but you put them heading opposite directions and they are now traveling at twice the speed of light... relative to each other.

Back to the wormhole on the Earth/ship reference. Again, if I am understanding what you are saying, when someone looks into either side of the wormhole, either from the ship or from Earth, everything appears slowed down. Again, that is if I am understanding what you are saying.

But, there is no FTL travel, or even any travel beyond what travel could be hand when looking from one room into another through a door frame. But, that is only if what I understand of wormholes to be correct and they are (put simply) just two sides of a 2 dimensional surface.


I have an idea, instead of replying back to this whole post, lets start from fresh.

A wormhole, is it just two sides of a two dimensional space where traveling between the two puts you from one point to the other by just taking a step through the opening? Where there is actually no space between the sides so no travel is had from entering to exiting. If there is a distance between the two sides, then how far is it? Does the distance between the containers of the openings affect the distance had between the entrance and exit?

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #36 on: June 16, 2012, 05:29:22 PM »
Not sure I understood everything you were talking about there, again, using the terminology that I am not fully educated in is only adding to the confusion.

I'm trying to avoid being too snarky, but there is plenty of information publicly available on the Internet to help you familiarize yourself with basic concepts of relativity and, most importantly for our discussion, the concept of frames of reference and the fact that there is no preferred frame.

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I understand that anything going over a distance is travel, but what distance is traveled between the wormhole sides? It's a 2 dimensional space, right?

No, I'm not sure why you would think this.

Take a balloon, pinch part of it together, poke a whole in the middle and seal the edges of the hole. The entire surface, including the 'wormhole', is two-dimensional. Scale this up a dimension, and the wormhole gains one too. The wormhole still has 'depth'.

However, it isn't remotely necessary for our discussion to be at all concerned with that. An ansible or other instant teleport device or reducing the wormhole to such is not necessary, it's just convenient, because it's where math as in the above is the most accurate.

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Someone walking at say, 2mph going into one side is walking the same 2mph coming out the other and if those ends of the wormhole are at opposite sides of the universe, does that mean that they have said ungodly high speed of some FTL travel, or were they only going at 2mph at all points?

It means they have violated the dominant energy condition. It's not generally appropriate to consider any sort of remotely physical (and physicists will probably poke at me for that, but whatever) faster-than-light travel to have 'a speed'. How fast something moves FTL is going to depend on the frame of reference of whomever is observing it. It is, in fact, possible for many FTL mechanisms to appear as slower than light in some suitably absurd frame of reference. Star Trek is the most typical example.

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It's well known that there are galaxies out there that are traveling away from us at speeds greater than the speed of light. It's not due to said galaxy actually traveling faster than the speed of light,

Correct.

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but due to our mutual speeds traveling away from a random set neutral point between our two galaxies and the expansion of the universe.

The former is meaningless. The latter is correct.

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At no point is any going FTL,

Correct.

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but combine all the factors and FTL is observed.

Incorrect. The expansion of spacetime across the Universe creates a horizon, past which we cannot observe. Therefore, while we are well aware of this phenomenon, the actual observation is not possible - the FTL is created because of the deformation of spacetime itself, and galaxies past this horizon cannot send a photon to reach us, thus preventing our observation.

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I don't like saying it this way, but it's one of the better ways of putting, all speed is relative. Two ships traveling in the same direction next to each other at the speed of light, relative to each other neither is traveling but you put them heading opposite directions and they are now traveling at twice the speed of light... relative to each other.

Incorrect. A ship moving at the speed of light would presumably have an infinite horizon, but if you have two ships at rest, and each moves in opposite directions away from each other at .9999 of c, they will each observe the other ship receding from them at a rate defined by the relativistic velocity addition formula.

(.9999 + .9999) / (1 + .9999^2) = 0.999999995

In order for the relative speed between them to actually exceed the speed of light, the expansion of space between them needs to be what pushes them over the edge. Much easier to just drop one into a black hole, but the finality of that might disturb the occupants of said ship.

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Back to the wormhole on the Earth/ship reference. Again, if I am understanding what you are saying, when someone looks into either side of the wormhole, either from the ship or from Earth, everything appears slowed down. Again, that is if I am understanding what you are saying.

While the faces of the wormhole have a relativistic speed difference, yes.

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But, there is no FTL travel, or even any travel beyond what travel could be hand when looking from one room into another through a door frame. But, that is only if what I understand of wormholes to be correct and they are (put simply) just two sides of a 2 dimensional surface.

We could pretend such a wormhole existed as a thought experiment, but it wouldn't change the reality that travel occurs.

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I have an idea, instead of replying back to this whole post, lets start from fresh.

A wormhole, is it just two sides of a two dimensional space where traveling between the two puts you from one point to the other by just taking a step through the opening? Where there is actually no space between the sides so no travel is had from entering to exiting. If there is a distance between the two sides, then how far is it? Does the distance between the containers of the openings affect the distance had between the entrance and exit?

I think you're confused.

You're declaring that it isn't travel by some sort of authorial fiat, like declaring pi to be 4.5 or the Sun to be a giant orange. Mass-energy has vanished from one part of the universe and appeared 100 light-years away. The distance is certainly much shorter in a very localized context, but a distant observer is still going to see a hundred light-years of near-instantaneous travel, and is going to have difficulty ordering the events on either side of the wormhole. That travel - regardless of the mechanism - still occurs.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #37 on: June 16, 2012, 08:29:07 PM »
I'm trying to avoid being too snarky, but there is plenty of information publicly available on the Internet to help you familiarize yourself with basic concepts of relativity and, most importantly for our discussion, the concept of frames of reference and the fact that there is no preferred frame.

At least you said you tried to avoid being snarky. And I could have sworn that I said
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Again, I've read a few books on this (they made my brain implode) and have watched many videos (Ted.com is awesome) but I've not found any that have really said anything that the way I'm seeing things is backwards.

And that my initial post was made at an early time, so it is very likely that my thinking was clouded.

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No, I'm not sure why you would think this.

Did a quick check and found a wormhole described in this way. Take a piece of paper and curve it, poke a hole through opposite ends that overlap and that is a simplified example of what a wormhole is, a shortcut between two otherwise very distant points. It may have been incorrect of me saying it was 2 dimensional, so lets say that the distance traveled in the wormhole that we do not have an method today to measure such a small space. I'm not finding any reason why there needs to be space between those two points inside the wormhole, so I simply was saying that it was a 2 dimensional "window" between two points.

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Take a balloon, pinch part of it together, poke a whole in the middle and seal the edges of the hole. The entire surface, including the 'wormhole', is two-dimensional. Scale this up a dimension, and the wormhole gains one too. The wormhole still has 'depth'.

Here it seems like you just contradicted yourself... you say that it's 2 dimensional yet then say it has depth. If we are referring to the entrance and exit to the wormhole having height and width, and it being a 2 dimensional surface, then how could it also have depth?

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It means they have violated the dominant energy condition. It's not generally appropriate to consider any sort of remotely physical (and physicists will probably poke at me for that, but whatever) faster-than-light travel to have 'a speed'. How fast something moves FTL is going to depend on the frame of reference of whomever is observing it. It is, in fact, possible for many FTL mechanisms to appear as slower than light in some suitably absurd frame of reference. Star Trek is the most typical example.


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The former is meaningless. The latter is correct.

Again, you confuse me. First you seem to say what I describe, then say it's meaningless then say I am correct again? In the example I was providing, I was saying how two ships moving away from a mutual neutral frame of reference. You say that is meaningless, but it is key to have a frame of reference or another point to compare to, to have any sort of speed. If there was a ship in a total void, how could you tell how fast it was going without anything to reference it to.

My phrasing may have confused you on what I was saying, so lets try this. You are the neutral point. You look left and see a point traveling away from you at 75% the speed of light, you look right and see another point traveling away also at 75% the speed of light. Using you as the neutral point, those two points are traveling away from each other at 150% the speed of light. Those two points being along the same line and opposite directions from each other.

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Incorrect. The expansion of spacetime across the Universe creates a horizon, past which we cannot observe. Therefore, while we are well aware of this phenomenon, the actual observation is not possible - the FTL is created because of the deformation of spacetime itself, and galaxies past this horizon cannot send a photon to reach us, thus preventing our observation.

And I was wrong with using "observe" at that point, but again it seems you are saying exactly what I've been trying to describe.

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Incorrect. A ship moving at the speed of light would presumably have an infinite horizon, but if you have two ships at rest, and each moves in opposite directions away from each other at .9999 of c, they will each observe the other ship receding from them at a rate defined by the relativistic velocity addition formula.

(.9999 + .9999) / (1 + .9999^2) = 0.999999995

In order for the relative speed between them to actually exceed the speed of light, the expansion of space between them needs to be what pushes them over the edge. Much easier to just drop one into a black hole, but the finality of that might disturb the occupants of said ship.

Here again you confuse me. You just said that the expansion of the universe, which I have no problems with and feel I've tried to get that point across, would make their speeds away from each other faster than the speed of light without either actually exceeding that speed itself. But here you say that they wouldn't be traveling away from each other faster than light?

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I think you're confused.

You're declaring that it isn't travel by some sort of authorial fiat, like declaring pi to be 4.5 or the Sun to be a giant orange. Mass-energy has vanished from one part of the universe and appeared 100 light-years away. The distance is certainly much shorter in a very localized context, but a distant observer is still going to see a hundred light-years of near-instantaneous travel, and is going to have difficulty ordering the events on either side of the wormhole. That travel - regardless of the mechanism - still occurs.

And yet I keep thinking you are the one being confusing. In this instance, I wasn't declaring anything, I was asking questions and giving a possible example to try and help clarify the question.

Now, from what I am understanding of what you are trying to tell me, is that it doesn't matter if someone is looking through the wormhole or looking from ship to Earth or back, the same would be viewed?

Wormholes and Time Travel - Ian Morison

That seems contrary to what he describes. Or, in my head it does at least. For what Ian Morison describes, what would be seen through the wormhole would be the same as looking through a window or into the next cabin on the ship. If time dilation was viewed through the wormhole, then the times differences of the two sides of the wormhole would be even greater by the time he returned to Earth.

Honestly, I feel we are saying the same thing, but putting it in such a way as to be confusing to the other. My original question, that being what would be observed, has been answered. I may not like the result, that being time travel is actually possible, but it's a result that I will have to be content with. At least until such a wormhole experiment is possible and tested to see if it really holds true. Thank you for you time.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #38 on: June 16, 2012, 10:15:06 PM »
At least you said you tried to avoid being snarky. And I could have sworn that I said 
And that my initial post was made at an early time, so it is very likely that my thinking was clouded.

Ted is cool but it's not a source of education about stuff like this.

I don't have the time to provide a full education. You're asking me to actually 'argue' very basic relativity with you. You make statements like:

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My phrasing may have confused you on what I was saying, so lets try this. You are the neutral point. You look left and see a point traveling away from you at 75% the speed of light, you look right and see another point traveling away also at 75% the speed of light. Using you as the neutral point, those two points are traveling away from each other at 150% the speed of light. Those two points being along the same line and opposite directions from each other.

This is false. If two things are moving away from each other faster than the speed of light, that means a photon cannot travel to one and then travel to the other. However, a photon most certainly can bounce between these spaceships nigh indefinitely in Minkowski spacetime.

The speed between the ships is given by the relativistic velocity addition equation that I linked. They are moving away from each other at
(.75 + .75) / (1 + .75^2) = .96 of c



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Did a quick check and found a wormhole described in this way. Take a piece of paper and curve it, poke a hole through opposite ends that overlap and that is a simplified example of what a wormhole is, a shortcut between two otherwise very distant points. It may have been incorrect of me saying it was 2 dimensional, so lets say that the distance traveled in the wormhole that we do not have an method today to measure such a small space. I'm not finding any reason why there needs to be space between those two points inside the wormhole, so I simply was saying that it was a 2 dimensional "window" between two points.

Here it seems like you just contradicted yourself... you say that it's 2 dimensional yet then say it has depth. If we are referring to the entrance and exit to the wormhole having height and width, and it being a 2 dimensional surface, then how could it also have depth?

Those are two-dimensional wormholes, in two-dimensional universes. They both have some concept of depth in those universes. You add a dimension to the universe, you add a dimension to the wormhole along with it.

It's not terribly relevant, regardless.

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Again, you confuse me. First you seem to say what I describe, then say it's meaningless then say I am correct again? In the example I was providing, I was saying how two ships moving away from a mutual neutral frame of reference. You say that is meaningless, but it is key to have a frame of reference or another point to compare to, to have any sort of speed. If there was a ship in a total void, how could you tell how fast it was going without anything to reference it to.

There does not need to be a mutual neutral frame of reference for the discussion - it merely adds complexity to an issue that, plainly, doesn't need to have complexity added. It's irrelevant, unless you're picking a point which is within both points' event horizons. But such points are merely useful for discussion about the issue - they aren't necessary to discuss spacetime's expansion and its effects.

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My phrasing may have confused you on what I was saying, so lets try this. You are the neutral point. You look left and see a point traveling away from you at 75% the speed of light, you look right and see another point traveling away also at 75% the speed of light. Using you as the neutral point, those two points are traveling away from each other at 150% the speed of light. Those two points being along the same line and opposite directions from each other.

See above. They are not moving apart at 1.5c, they are moving apart at .96c.

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And I was wrong with using "observe" at that point, but again it seems you are saying exactly what I've been trying to describe.

You're still having issues with normal motion versus recession caused by the expansion of spacetime.

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Here again you confuse me. You just said that the expansion of the universe, which I have no problems with and feel I've tried to get that point across, would make their speeds away from each other faster than the speed of light without either actually exceeding that speed itself. But here you say that they wouldn't be traveling away from each other faster than light?

They would not. If two things are moving apart faster than light, that means a photon cannot cross the gap between them. It requires an exceptional situation for this to occur.

Main subject to look up, here, is Lorentz Contraction. You move at .86c in a direction, distance is compressed along that direction by a factor of 2.  This includes behind you. Thus, you need a different equation when adding the velocities, as I linked.

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And yet I keep thinking you are the one being confusing. In this instance, I wasn't declaring anything, I was asking questions and giving a possible example to try and help clarify the question.

Now, from what I am understanding of what you are trying to tell me, is that it doesn't matter if someone is looking through the wormhole or looking from ship to Earth or back, the same would be viewed?

Not sure what you mean by 'same' here.

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Wormholes and Time Travel - Ian Morison

That seems contrary to what he describes. Or, in my head it does at least. For what Ian Morison describes, what would be seen through the wormhole would be the same as looking through a window or into the next cabin on the ship. If time dilation was viewed through the wormhole, then the times differences of the two sides of the wormhole would be even greater by the time he returned to Earth.

Having it return to Earth makes for fewer headaches, like trying to seriously answer 'could his wife actually look at Andromeda after only four hours?'

Regardless, it's true - 4 hours later, 2.5myear difference, 8 hours, 5myear.

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Honestly, I feel we are saying the same thing, but putting it in such a way as to be confusing to the other. My original question, that being what would be observed, has been answered. I may not like the result, that being time travel is actually possible, but it's a result that I will have to be content with. At least until such a wormhole experiment is possible and tested to see if it really holds true. Thank you for you time.

And that isn't, actually, what I said.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #39 on: June 17, 2012, 01:54:59 AM »
And that isn't, actually, what I said.

Ok, will try one more time, starting over from scratch. We know the chorus by now, ship traveling at near speed of light, wormhole on ship and on Earth.

Now, to put my original question as simply as I can, what would a person see when looking into the wormhole on the ship?

My challenge to you, answer it as if a 12 year old asked you that question.

I put it this way due to a lot of frustration I am having at your answers seeming to contradict other answers you give also in you saying I am wrong when I try and put what you say into a more simple form that seems nearly identical to what you say, but again say I am wrong. I would really like a 3rd person to read over this whole line and say if I am just seeing what isn't there or if some of your answers really do seem to contradict each other. Regardless, this will most likely be one of, if not my last, post along this thread, but I do wait with baited breath for your final attempt at the challenge I have put forth.

Offline AndyZTopic starter

Re: Physics/Theory of Relativity questions
« Reply #40 on: June 17, 2012, 02:21:03 AM »
I've been watching this thread, and here's a question from me:

Incorrect. A ship moving at the speed of light would presumably have an infinite horizon, but if you have two ships at rest, and each moves in opposite directions away from each other at .9999 of c, they will each observe the other ship receding from them at a rate defined by the relativistic velocity addition formula.

(.9999 + .9999) / (1 + .9999^2) = 0.999999995

In order for the relative speed between them to actually exceed the speed of light, the expansion of space between them needs to be what pushes them over the edge. Much easier to just drop one into a black hole, but the finality of that might disturb the occupants of said ship.

Please point out my flaw.

Now, let's say that at point O, two spaceships blast off away from each other, each going at .9999 C.  To an observer watching at point O, the distance between the two would increase at a rate equal to 1.9998 C.  This would mean that as O watches (ignoring the fact that he needs light to watch and that he would have to use redshifting and calculations to figure out actual time), the light created by the rocket of one ship would never be able to bounce off of the other.  The two ships would not be able to see each other.

Now, from the perspective of one ship, the distance between the two is increasing at a rate of  0.999999995 C.  This would mean that, however long it would take, light created by the rocket of one ship would be able to bounce off of the other ship.  The people on each ship would still be able to see each other.

Please point out my flaw.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #41 on: June 17, 2012, 02:44:25 AM »
I've been watching this thread, and here's a question from me:

Please point out my flaw.

Now, let's say that at point O, two spaceships blast off away from each other, each going at .9999 C.  To an observer watching at point O, the distance between the two would increase at a rate equal to 1.9998 C.  This would mean that as O watches (ignoring the fact that he needs light to watch and that he would have to use redshifting and calculations to figure out actual time), the light created by the rocket of one ship would never be able to bounce off of the other.  The two ships would not be able to see each other.

Now, from the perspective of one ship, the distance between the two is increasing at a rate of  0.999999995 C.  This would mean that, however long it would take, light created by the rocket of one ship would be able to bounce off of the other ship.  The people on each ship would still be able to see each other.

Please point out my flaw.

Do a mental experiment for a moment.

Give person O a laser pointer, and a mirror on the back of each ship (call them A and B)

O points the laser at A's mirror. It eventually reaches A (because we all agree that it can reach it. Hits it, and bounces back - extremely redshifted, but it's still bouncing back. Because it's returning at the speed of light from all frames of reference, it will eventually reach O's position again, and assuming O steps out of the way, will be racing towards B - still at the speed of light. Possibly redshifted beyond any hope of retrieval, but maybe it's an X-ray laser or something. The light bounces off of B's mirror, and O will see it, some significant time later. Or O can step out of the way and watch it hit A again, let it bounce back to B again... as often as O likes until it's so redshifted that it isn't able to be distinguished from background radiation.

Does that help?

Offline AndyZTopic starter

Re: Physics/Theory of Relativity questions
« Reply #42 on: June 17, 2012, 02:50:13 AM »
Yes.  Thank you.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #43 on: June 17, 2012, 03:02:27 AM »
There are a lot of fun paradoxes with Relativity.

The Ladder Paradox:

A farmer has a barn, 20 units long. A runner has a ladder, 30 units long.

The runner starts running towards the open barn at .86 of c. The barn appears, to the runner, to be 10 units long.

To the farmer, the runner's ladder is 15 units long. Once the runner is entirely inside, the farmer has had enough of these relativistic hijinx and closes the barn doors, and the runner is completely inside the barn - 15 unit ladder and all.

The farmer's son considers the runner a friend, or at least doesn't feel like cleaning up the mess. He presses the button, the doors open an instant later, and the runner continues on his way.

How is this possible?

The answer is of course on-line, but there's at least one clue to it in this thread.

*snip* I do wait with baited breath for your final attempt at the challenge I have put forth.

If all I'm going to get are sarcastic quips, I'll spend my time on others, instead.

Offline AriDarrow

Re: Physics/Theory of Relativity questions
« Reply #44 on: June 17, 2012, 03:25:42 AM »
I've been watching this thread, and here's a question from me:

Please point out my flaw.

Now, let's say that at point O, two spaceships blast off away from each other, each going at .9999 C.  To an observer watching at point O, the distance between the two would increase at a rate equal to 1.9998 C.  This would mean that as O watches (ignoring the fact that he needs light to watch and that he would have to use redshifting and calculations to figure out actual time), the light created by the rocket of one ship would never be able to bounce off of the other.  The two ships would not be able to see each other.

Now, from the perspective of one ship, the distance between the two is increasing at a rate of  0.999999995 C.  This would mean that, however long it would take, light created by the rocket of one ship would be able to bounce off of the other ship.  The people on each ship would still be able to see each other.

Please point out my flaw.

But, with the expansion of space, wouldn't the combination of the distance between the two ships as well as the rate at which the space between them expanding make it, at some point, impossible for the ships to see each other?

Offline piece

Re: Physics/Theory of Relativity questions
« Reply #45 on: June 17, 2012, 12:09:49 PM »
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There are a lot of fun paradoxes with Relativity.

The Ladder Paradox:

A farmer has a barn, 20 units long. A runner has a ladder, 30 units long.

The runner starts running towards the open barn at .86 of c. The barn appears, to the runner, to be 10 units long.

To the farmer, the runner's ladder is 15 units long. Once the runner is entirely inside, the farmer has had enough of these relativistic hijinx and closes the barn doors, and the runner is completely inside the barn - 15 unit ladder and all.

The farmer's son considers the runner a friend, or at least doesn't feel like cleaning up the mess. He presses the button, the doors open an instant later, and the runner continues on his way.

How is this possible?

Wouldn't this go back to the concept of that frame of reference, and with the original question Ari posed about what would be seen via the wormhole?

I am by no means highly educated in this subject, but I'd like to take a stab here. And I'm perfectly willing to sound foolish if I learn from it! I have heard of this paradox before, but I don't fully grasp all the mechanics and principles behind it.

So, here goes. The ladder appears to be moving really, really fast to the barn, and the barn would appear to be moving really, really fast to the ladder. So the ladder, as seen from the barn, would be 15 units long, which would fit in the actual 20 unit space of the barn. From the barn's frame of reference, the ladder fits.

But what happens from the ladder's frame of reference? That's what I'm not completely sure how to reconcile, because going from the ladder's point of reference, the barn would only be 10 units in length. Help, please?

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #46 on: June 17, 2012, 12:35:35 PM »
The answer has been hinted at in this thread.

Blatant hint
'Now' is relative. Events that are simultaneous from one perspective are not necessarily simultaneous from another, and spacelike events (events not within each others' light cones) cannot have any special ordering according to relativity - A->B or B->A depends on the observer.

Constructing a mechanism that permits FTL and maintains Causality requires that there be a correct special ordering. However, people would still observe the incorrect ordering from some frames.

Offline piece

Re: Physics/Theory of Relativity questions
« Reply #47 on: June 17, 2012, 02:18:57 PM »
Oh! Now it makes much more sense to me! The paradox isn't just in the ladder fitting in the barn, but also the boy opening the door.

Offline Vekseid

Re: Physics/Theory of Relativity questions
« Reply #48 on: June 17, 2012, 02:31:55 PM »
Not exactly.

Spoiler: Click to Show/Hide
The doors closing and opening are separate events, A and B. They are not within each others light cone, so there is no true ordering as to which is actually first. To the farmer and his son, events A and B are simultaneous. Now thing about what the runner will see.
[/quote]

Offline piece

Re: Physics/Theory of Relativity questions
« Reply #49 on: June 17, 2012, 04:35:54 PM »
Spoiler: Click to Show/Hide
So...

If A and B are simultaneous from the perspective of the farmer and his son, in the barn, they might not be from the runner's perspective with the ladder? If there's no ordering of A and B from the runner's perspective, the two events can happen in a different order than what the farmer saw.

Which would mean B can precede A from a different frame of reference.

Without an understanding of the math behind it, I'm still looking at this from a weak position, but I think I see how that would eliminate the paradox of the ladder not fitting for the runner. It wouldn't ever actually be closed in, if the rear doors opened before the front door closed, if I'm understanding rightly?