Understanding Relativity and Its Effects on Lightspeed

[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.

 

[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.