Wormholes in Space

[Sindri]

Originally Posted by lwcamp

This is one possibility. Another possibility is that the topology of space-time fundamentally cannot be changed. If this were the case, you simply cannot ever create wormholes to another part of this universe, but any wormholes left over as relics of creation (if any) cannot ever fully collapse. They can shrink down to specks on the order of the Plank scale, but if you find one, you can always pump it back up with negative energy stuff and see where the other end is located.

Another nifty thing - if the topology of space-time cannot change, you can pump massive amounts of energy into a tiny speck of it to initiate inflation, and then this universe will always be connected to the universe you just created with a wormhole. Use time dilation tricks to wait until things have quieted down and you have stars and planets and stuff, then open up the wormhole to see where it goes (there are ways to propel and steer wormholes from the other side, making use of time dilation effects to mean everyone at home doesn't have to wait long even though the wormhole on the other side might experience thousands of years of proper time en route to its new home).

At this time, we have no experimental or theoretical justification for preferring topology changing versus non-topology changing physics.

Luke

Let me see if I understand this properly. By arbitrarily stating that the universe's topology is unchangeable I can get a finite unkillable wormholes around this universe and new wormholes go to new universes?

Do you think the wormholes left over from creation would be all over the place or rare if they existed?

[lwcamp]

Originally Posted by Sindri

Let me see if I understand this properly. By arbitrarily stating that the universe's topology is unchangeable I can get a finite unkillable wormholes around this universe and new wormholes go to new universes?

Yes. And unkillable wormholes to other universes.

If topology changes are allowed, you can still make and get wormholes to other universes, but they can collapse, forever pinching off the new universe, if you are not careful with them.

In a universe that allows topology changes, you can get wormholes that cannot completely collapse if you introduce what is called a "conserved topological charge" during their creation. This is a flux of some field without a charge carrier that threads the mouth of the wormhole, such as a magnetic field. A fully collapsed wormhole can only go down to about the Planck scale and is then prevented from completely pinching off by the threaded field. At this point, the wormhole acts like a charge carrier for that field. It can only completely go away if it meets another wormhole mouth with the field going the other way (something like matter and antimatter), which would probably result in the two left-over mouths being linked to each other, or if it met its own other mouth, which would completely destroy the wormhole.

Originally Posted by Sindri

Do you think the wormholes left over from creation would be all over the place or rare if they existed?

Relics of creation would probably have been extraordinarily diluted during the inflationary period of our universe, making them extremely rare.

Probably.

We guess.

Fact is, we are often surprised by all sorts of things in science - no one expected the bizarre zoo of exoplanets we have seen, for example.

So, going back to the idea of wormholes with conserved topological charge acting as if they were charge carriers - what if all fundamental electrically charged particles were actually wormholes, with the electric field the thing that prevents them from going away? Now every electron in the universe is a wormhole that leads to some other positive charge (this version probably requires quarks to be quasiparticle excitations in a field with charge +/- 1, so most electrons will link up to a proton). You will not have any idea where a particular electron will go until you try it, but you will have LOTS and LOTS of opportunities to try!

Luke

[Tuoni]

lwcamp . . . you are my most favourite person ever.

[Sindri]

He's pretty awesome.

Regarding wormholes is it possible to construct a system of wormholes where you can go somewhere and come back relatively quickly without being able to shoot yourself in the back or other time travel shenanigans?

[sir_pudding]

Originally Posted by lwcamp

In general relativity, you have to be careful about this. All wormholes have regions which have negative energy densities (which is more or less equivalent to negative mass density), but the far-field curvature of space-time commonly matches that of a body of zero or positive mass, so that they would behave like a body with zero or positive mass. There are good reasons to believe that quantum mechanics forbids net zero or negative mass bodies (the statement is more sophisticated than this, but this helps you get the idea). So you end up with an object that essentially has a positive mass.

Interesting. I probably already should have known that. Thank you.

Now, it is quite likely that the mass will be very large - the mass of Jupiter, the mass of a million suns, something like that. This depends on the particular implementation of the wormhole.

Well parking a Jupiter or a million suns on a planet is also something to avoid. :)

A million suns would easily put it in the OP's desired "outside of Pluto's" range. :)

[Sindri]

Originally Posted by sir_pudding

A million suns would easily put it in the OP's desired "outside of Pluto's" range. :)

That was just an example really. I'd just like it to be within reasonable torch access as opposed to requiring a substantial journey in it's own right. I should crunch some numbers on how close I'd like it.

[lwcamp]

Originally Posted by Sindri

Regarding wormholes is it possible to construct a system of wormholes where you can go somewhere and come back relatively quickly without being able to shoot yourself in the back or other time travel shenanigans?

It is possible. It is suspected (although not proven) that any configuration of space-time that allows time-travel paradoxes is unstable due to quantum fluctuations. Think of it this way - a quantum fluctuation can propagate around the same closed curve to arrive back where it started, thus amplifying itself. This gives you a resonator that drives these virtual excitations to very large amplitudes, which then destroys your time machine. Any wormhole or configuration of wormholes that would allow you to shoot yourself in the back of the head would destroy itself before it could form.

What is left are space-time configurations that cannot loop back on themselves to the same place and time. This prevents paradoxes.

Wormholes always allow a limited form of time travel - they connect one location in space and time to another location in space and time, and the two times do not necessarily need to have the same coordinate measure. But if the wormholes are far enough separated in space, such that a light speed signal cannot get from one to the other in less time than the time jump when going between them, there is no paradox and none of the disturbing issues you get from unlimited time travel.

Luke

[lwcamp]

Originally Posted by sir_pudding

Interesting. I probably already should have known that. Thank you.

You can see this in wormhole geometries that are "cut-and-paste" of other, known, geometries. The classic Morris-Thorne wormhole takes two Schwarzschild metrics, cuts off the "bottoms" (the high gravity, low radius part) and stitches the two together at the cut with their negative mass stuff (the Casimir vacuum, in this case). Since everywhere except at the "stitches," the space-time has the Schwarzschild geometry, it acts to particles in that space-time as if affected by the mass of an object with the mass of the thing that made the original Schwarzschild gravity well.

Another example is the Visser wormhole, which cuts a hypersurface out of two separate Minkowski space-times and stitches them together at the hypersurface cut. Since these are made from Minkowski space-time, there is zero curvature everywhere except at the "stitches" and there is no gravity. These wormholes are identically massless. (Actual implementations of wormholes that are approximations of Visser wormholes would probably have a small but finite positive mass).

Luke

[Sindri]

Originally Posted by lwcamp

It is possible. It is suspected (although not proven) that any configuration of space-time that allows time-travel paradoxes is unstable due to quantum fluctuations. Think of it this way - a quantum fluctuation can propagate around the same closed curve to arrive back where it started, thus amplifying itself. This gives you a resonator that drives these virtual excitations to very large amplitudes, which then destroys your time machine. Any wormhole or configuration of wormholes that would allow you to shoot yourself in the back of the head would destroy itself before it could form.

What is left are space-time configurations that cannot loop back on themselves to the same place and time. This prevents paradoxes.

Wormholes always allow a limited form of time travel - they connect one location in space and time to another location in space and time, and the two times do not necessarily need to have the same coordinate measure. But if the wormholes are far enough separated in space, such that a light speed signal cannot get from one to the other in less time than the time jump when going between them, there is no paradox and none of the disturbing issues you get from unlimited time travel.

Luke

I've heard about the chronology protection conjecture. It's very convenient!

So we avoid the important variety of time travel by having a time jump as well as a spatial jump, is that right?

How does this interact with multiple stops? Would it require something like a central hub that everything goes from or can you link it up more?

Is travel through a wormhole instantaneous or can there be travel time from the perspective of the traveller?

[Flyndaran]

So instant to the traveler, but light speed to the rest of the universe is ok?