Understanding Relativity and Its Effects on Lightspeed

[Ambitwistor]

Originally posted by dace
Ordinarily, when someone undergoes velocity-induced time dilation, they will not find themselves in the past but only younger in the present (twins paradox). So why does the wormhole negate the usual effect?

The wormhole doesn't "negate" any time dilation. Someone spun in a the centrifuge undergoes time dilation whether or not there is a wormhole nearby.

Fred passes through the wormhole and drops back in time by 55 seconds. Why?

Because the wormhole mouth is connected to another wormhole mouth at a different time.

The mouth of the wormhole itself is still fully present, its five seconds dilated twelve-fold into a full minute.

But the other wormhole mouth that it is connected to, in the lab, has only experienced five seconds of laboratory time. When you travel through a wormhole, you are jumping from one event to another. There is nothing that says that those two events have to be simultaneous according to a particular observer.

In fact, why would anything happen to him at all? It was the mouth of the wormhole that got spun and dilated in time, not Fred.

Yes, that's the point. Fred, Francine, or Frank (who stayed in the laboratory the whole time and was never spun) can all step through the spun wormhole mouth and emerge 55 seconds in the past. The time travel is all due to the wormhole, not due to what happened to any particular observer before he steps through the wormhole.

Of course, if the wormhole mouth did drop back into the past, Fred could not enter it anyway because he's presumably still in the present, like everyone else.

The spun wormhole mouth doesn't "drop into the past"; it's simply connected to another wormhole mouth (in the lab) that is in the past.

What is so special about a wormhole? Why would it transfer its dilated time to someone passing through it?

A wormhole doesn't "transfer dilated time". It just let's you travel directly to whatever event the opposite mouth is at.

And more importantly, why does it enable you to exchange your five slowed-down seconds for five "normal" seconds when you come out?

I don't know what you're talking about. This has nothing to do with whether you experienced any time dilation yourself.

Look, what do you think ought to happen instead?? Think carefully about what it means for a wormhole to exist, and what you will see:

If I'm on one side of a wormhole mouth and my friend is on another, then I can in principle reach through it and touch him: when I reach through it, his clock won't be moving fast or slow or anything --- no matter how he and the wormhole are moving: he will just be sitting there, like I am, holding a normal conversation with me. I can reach through the wormhole mouth and grab his wrist and look at his wristwatch --- even pull his arm through the wormhole into my lab if I want a closer look --- and check the time: his watch will be ticking normally. Do you disagree with this?

So, put him and his wormhole mouth in a centrifuge for a minute according to me (five seconds according to him). Suppose he grabs my hand just as the centrifuge starts, and says he'll let go as soon as the centrifuge stops. Then I see the centrifuge start to spin.

According to him in the centrifuge, he stops after five seconds and let's go of my hand. But of course he's only been holding my hand for five seconds according to me, too, and we've only had time for five seconds of conversation through the wormhole. The centrifuge next to me with him and his wormhole mouth in it are still spinning, of course, and will continue to do so for 55 more seconds on my watch. Do you disagree with that?

After that five seconds has elapsed and he let's go of my hand, I grab his arm and haul him through his wormhole mouth, through mine, into the lab. He's standing next to me, five seconds elapsed on his watch, five seconds elapsed on mine, while the centrifuge is still spinning. Do you disagree with that?

55 seconds later, the centrifuge stops. I look in, and see him get hauled into his wormhole mouth arm-first, whereupon he disappears from the lab. I peer into the wormhole mouth, and see him and I, 55 seconds in the past. Do you disagree with that?

Drop all this abstract "swapping time dilated seconds for normal seconds" nonsense. Which part of what actually happens do you disagree with? Which description that I gave, specifically, is the one that you think is impossible? Where does your agreement with me begin to diverge? In the very first part of my description of the scenario, or later on?

 

[dace]

Because the wormhole mouth is connected to another wormhole mouth at a different time.

This is really the core of our disagreement. Both mouths of the wormhole occupy the same time. That one mouth is spun at high velocity doesn't mean it drops back to another time. It merely dilates, aging less than it should while remaining present.

It's the same thing with muons or other particles sent through a collider. Do the muons actually drop back in time or merely decay less than normal?

The spun wormhole mouth doesn't "drop into the past"; it's simply connected to another wormhole mouth (in the lab) that is in the past.

This doesn't make sense. Certainly the wormhole mouth that hasn't been spun is not in the past. That's not the issue. The issue is whether the mouth that has been spun is in the past. I'm saying that it would not be in the past either, according to the principles of time dilation.

According to him in the centrifuge, he stops after five seconds and let's go of my hand. But of course he's only been holding my hand for five seconds according to me, too, and we've only had time for five seconds of conversation through the wormhole. The centrifuge next to me with him and his wormhole mouth in it are still spinning, of course, and will continue to do so for 55 more seconds on my watch. Do you disagree with that?

His five seconds will equal one minute for you, since you are not in the centrifuge. When you pull him out through the wormhole, five seconds will have passed for him and one minute for you and the lab. He has never left the present but only aged 55 seconds less than normal.

 

[Ambitwistor]

Originally posted by dace
This is really the core of our disagreement. Both mouths of the wormhole occupy the same time.

What does it mean for the wormhole mouths to "occupy the same time"? If I spin one wormhole mouth and take it out of the centrifuge, both mouths are still there at the same time, but they're not connected to each other at the same time: one mouth at one time is connected to the other mouth at a different time.

That one mouth is spun at high velocity doesn't mean it drops back to another time. It merely dilates, aging less than it should while remaining present.

The spun wormhole mouth doesn't go back in time. It time dilates like you said. But it's still connected to the other wormhole mouth at an earlier time.

It's the same thing with muons or other particles sent through a collider.

<sigh> No, it isn't. That's what I keep telling you. Particles in a collider can't jump to completely distant spacetime events.

This doesn't make sense. Certainly the wormhole mouth that hasn't been spun is not in the past. That's not the issue. The issue is whether the mouth that has been spun is in the past.

Read what I said. I didn't say that the spun wormhole mouth travels into the past. I said that it's connected to the unspun wormhole mouth in the past.

His five seconds will equal one minute for you, since you are not in the centrifuge. When you pull him out through the wormhole, five seconds will have passed for him and one minute for you and the lab. He has never left the present but only aged 55 seconds less than normal.

Okay, so you disagreed with my very first statement: that through the wormhole, his time passes at the same rate as yours. So, for instance, you disagree that you can talk to him through the wormhole normally; you disagree that he can grab your hand through the wormhole without his hand being time dilated; you disagree that after five seconds (according to you in the lab), he let's go of your hand. Is that right?

If so, sorry, but that's how wormholes work: no matter how the other end of the wormhole is moving with respect to you, there is no time dilation through the wormhole.

 

[Ambitwistor]

Originally posted by David
Although it is commonly called “time dilation,” it’s actually a “clock rate change” (a slowdown or speedup) caused by some sort of force placed on or removed from the fundamental mechanism of the clock, or a changing force being felt by the clock mechanism.

Not in general relativity, it isn't. Gravity doesn't even exert a force on a body.

Do you know of any kind of clock that doesn’t measure time by means of some kind of physical vibration or motion taking place inside or at the clock or a motion of the clock relative to something else?

Radioactive decay, for one. (Anticipating your response: no, radioactive decay rates of particles aren't determined by how fast something inside the particle is vibrating around.)

For that matter, atomic clocks have nothing to do with the oscillation rates or velocities of atoms or particles in atoms; they measure time according to the frequency of photons emitted by electronic energy transitions. (The frequency is determined by the energy gap, not by the rate at which electrons transition between energy levels or anything.)

I understand that a high gravitational potential speeds up pendulum clocks while it slows down atomic clocks at the same location,

Gravitational time dilation affects all clocks equally, no matter what their construction. The problem with a pendulum clock, however, is that it is designed to only work in one gravitational field. Even in Newtonian gravity, a pendulum clock will tick at different rates at different gravitational potentials; this has nothing to do with gravitational time dilation, which Newtonian gravity does not possess

 

[dace]

Originally posted by Ambitwistor
I didn't say that the spun wormhole mouth travels into the past. I said that it's connected to the unspun wormhole mouth in the past.

Nor did I claim that it travels to the past. Davies claims that it progresses through time more slowly and therefore falls back into the past as the rest of the world proceeds into the future. But it does not progress through time more slowly and does not remain in the past. It stays present while aging more slowly. This is because time-slowing equals time-stretching. Davies appears to be decoupling the concepts, which was the source of my original confusion. I appreciate that you cleared up my confusion on this point. However, in the process you've helped me understand why Davies' model is invalid.

What does it mean for the wormhole mouths to "occupy the same time"? If I spin one wormhole mouth and take it out of the centrifuge, both mouths are still there at the same time, but they're not connected to each other at the same time: one mouth at one time is connected to the other mouth at a different time.

So the mouths of the wormhole are in the same time and are not in the same time. I assume you mean that they're in the same time externally but at different times internally. But it doesn't matter how you slice it; they're still in the same time. The mouth that gets spun in the centrifuge does not recede into a different time but merely ages more slowly while remaining present.

If so, sorry, but that's how wormholes work: no matter how the other end of the wormhole is moving with respect to you, there is no time dilation through the wormhole.

I understand that there's no dilation from one end of the wormhole to the other. It doesn't matter as long as both mouths of the wormhole occupy the same timeline.

 

[Ambitwistor]

Originally posted by dace
However, in the process you've helped me understand why Davies' model is invalid.

Davies' model is valid, assuming it's the same as the Thorne model I'm describing.

So the mouths of the wormhole are in the same time and are not in the same time.

The spun wormhole mouth at lab time T=1 minute is linked to the unspun wormhole mouth at lab time T=5 seconds. It is not linked to the unspun wormhole mouth which is sitting right next to it at lab time T=1 minute.

The mouth that gets spun in the centrifuge does not recede into a different time but merely ages more slowly while remaining present.

For the Nth time: you're right that the spun wormhole does not "recede in time". But it is still linked to the unspun wormhole at an earlier time.

I understand that there's no dilation from one end of the wormhole to the other.

If you accept that, then you are logically forced to accept time travel. You admit that when the spun observer's watch reads 5 seconds, as seen by the lab observer through the wormhole, the lab observer's watch also reads 5 seconds. You also admit that when the spun observer's watch reads 5 seconds, the centrifuge stops. There is nothing preventing the spun observer from immediately stepping through the wormhole and meeting the unspun observer, when both of their watches still read 5 seconds.

It doesn't matter as long as both mouths of the wormhole occupy the same timeline.

I don't even know what it means for both mouths to "occupy the same timeline". Does that mean that they both exist at the same time, according to some observer? If so, fine, but that doesn't mean that they are connected at that same time.

 

[Janus]

Mentor note: I split off the discussion between David and Ambitwistor to a new thread of the same name to be found in the theory development forum

 

[dace]

There is nothing preventing the spun observer from immediately stepping through the wormhole and meeting the unspun observer, when both of their watches still read 5 seconds.

I do not agree that both of their watches read 5 seconds. After Fred returns from his ride in the centrifuge, his watch reads five seconds. But Frank, who merely watched the ride, shows 1 minute on his watch. The reason Fred's watch shows only 5 seconds is that the high speed at which he traveled dilated him in time twelve-fold, so that his 5 seconds are stretched out to equal one minute of "normal" time. He has not dropped into the past but simply aged 55 seconds less than normal.

The wormhole is neither here nor there (so to speak). It doesn't matter whether a wormhole mouth has been sent through the centrifuge along with Fred. It doesn't matter whether Fred steps through this wormhole to get back to the lab or just walks through a door. The wormhole cannot transmute Fred's 5 dilated seconds into 5 normal seconds. Regardless of how Fred returns to the lab, his 5 seconds will equal the 1 minute that passed outside the centrifuge, and he will not be back in time.

The mind can play tricks on us. A seemingly magical element comes along, in this case the wormhole, and all judgment is suspended. Surely the fabulous wormhole will not let us down! Like Dorothy, who disovers that the power to get back to Kansas is within her, we cannot travel back to the past except in our minds.

By the way, Davies credits Thorne for the model, with the only change being that Thorne attaches a mouth of the wormhole to a rocket while Davies attaches it to a centrifuge. Davies also points out that gravity will have the same effect, with one end of the wormhole placed near a neutron star.

 

[Ambitwistor]

Originally posted by dace
I do not agree that both of their watches read 5 seconds.

Now you're contradicting yourself; you said that you agreed that the watches tick at the same rate through the wormhole.

So, I take it that I was right:

Okay, so you disagreed with my very first statement: that through the wormhole, his time passes at the same rate as yours. So, for instance, you disagree that you can talk to him through the wormhole normally; you disagree that he can grab your hand through the wormhole without his hand being time dilated; you disagree that after five seconds (according to you in the lab), he let's go of your hand.

You disagree with all of those statements. But it is a simple fact that you can do all of those things, if a wormhole is present: that's the definition of a wormhole.

After Fred returns from his ride in the centrifuge, his watch reads five seconds. But Frank, who merely watched the ride, shows 1 minute on his watch.

That's fine, but 55 seconds earlier on Frank's watch, when Frank's watch read 5 seconds, Fred's watch also read 5 seconds, through the wormhole, and Fred can step through the wormhole at that time.

The reason Fred's watch shows only 5 seconds is that the high speed at which he traveled dilated him in time twelve-fold, so that his 5 seconds are stretched out to equal one minute of "normal" time. He has not dropped into the past but simply aged 55 seconds less than normal.

For the N+1th time, Fred doesn't drop into the past by being centrifuged. Fred, Frank, or anybody else can drop into the past, regardless of whether they were centrifuged or time dilated with respect to anyone, if they step through the spun wormhole mouth.

It doesn't matter whether a wormhole mouth has been sent through the centrifuge along with Fred.

Of course it does. If you just have two synchronized wormhole mouths, then if you step through one of them, you will immediately appear out the other at the same time. It's only if you centrifuge one of them that the mouths are connected to each other at different times.

The wormhole cannot transmute Fred's 5 dilated seconds into 5 normal seconds.

Nobody's dilated seconds are being "transmuted", traded or anything else. Why do you keep repeating yourself after being corrected several times? It doesn't matter whether Fred experiences any time dilation: he can still go back in time if one of the wormhole mouths experiences time dilation, and so can anybody else, time dilated or not.

Regardless of how Fred returns to the lab, his 5 seconds will equal the 1 minute that passed outside the centrifuge, and he will not be back in time.

Your statement is has nothing to do with the predictions of general relativity, or even logic.

 

[dace]

Fred's 5 seconds in the centrifuge equal Frank's 60 seconds in the lab. If Fred pulls Frank's arm into the wormhole, then Frank's watch will also be dilated 12-fold and will show only 5 seconds passing. However, unbeknownst to Fred, Frank is wearing a second watch on his other arm, and when he pulls his dilated arm from the wormhole, he compares watches and finds that the dilated watch reads 5 seconds while the one on his other arm reads 60 seconds. This does not mean that his dilated arm is now 55 seconds behind the other arm in time. Both his arms are fully present at his sides, but one of them is now 55 seconds younger than the other.

That's fine, but 55 seconds earlier on Frank's watch, when Frank's watch read 5 seconds, Fred's watch also read 5 seconds, through the wormhole, and Fred can step through the wormhole at that time.

...and cash in his 5 dilated seconds for 5 normal seconds. That's what you're saying. Somehow, through the magic of wormholtronics, Fred's 5 slowed-down seconds in the wormhole are translated into 5 normal seconds when he leaves the wormhole through the stationary end. What this means, in effect, is that the slowing down of time is decoupled from the stretching out of time. If time is slowed down, then by logical necessity, the interval between events is stretched out. As Lurch stated, when it comes to time, slowing down and stretching out are two different ways of saying the exact same thing. Ordinarily, as with the twins paradox, we recognize this. But when a wormhole shows up, it's like we're hypnotized, and all of a sudden we imagine that when time slows down, instead of stretching out and remaining present while aging less, it literally recedes into the past.

Fred, Frank, or anybody else can drop into the past, regardless of whether they were centrifuged or time dilated with respect to anyone, if they step through the spun wormhole mouth.

Wormholes are no different from anything else. You can spin one end of it as long as you want, but all it does is to dilate in time, to stretch out the intervals so that it's still at the same time as the other end. Yes, wormholes have a special property of internally connecting one place to another, but both places are always going to be in the same timeline. The difference we see from one end of the wormhole to the other is not a difference in time but a difference in age. The spun end is younger. That's it. No magic show.

Nobody's dilated seconds are being "transmuted", traded or anything else. Why do you keep repeating yourself after being corrected several times?

Because you keep demonstrating that you're not following.

Your statement is has nothing to do with the predictions of general relativity, or even logic.

Logic? Time travel to the past opens up insoluble paradoxes. Not exactly logical.

When something vanishes into the past, the matter-energy comprising it is gone. Meanwhile, back in the past, it's now doubled up, a copy having been produced out of seemingly nothing. If Fred is waving at himself 55 seconds in the past, he's been destroyed in the present and copied in the past.

Now take a look at the following syllogism:

1. No energy can be created or destroyed
2. Time travel entails both the creation and destruction of energy.
3. Therefore, time travel is impossible.

Now that's logic.