What is there actually to say of wormholes at the moment?

[TubbaBlubba]

I understand what wormholes are to a layman's degree, and perhaps a bit more - a "portal" in the structure we call spacetime. What I do not understand is why we consider their existence at all. (kind of like the superstrings, ho ho ho)

I've come to understand that there is some reason to believe they pop up here and there at subatomic level, but once again, nothing beyond that.

I can appreciate the idea of how our universe could be wrapped in a superdimensional manner which could allow for "shortcuts", similar to how you could go to one pole of a sphere to the other through the sphere rather than going all the way around (in a 2-dimensional world, that is), but other than fantasies and dreams of FTL travel, is there a good reason to believe they actually exist?Oh yes, a small question (mostly unrelated) - How does a photon react to gravity? I know it's pulled in by black holes, but in what manner? Do they immediately change direction towards the black hole at c, or do they orbit around it ad infinitum, getting closer and closer? The second seems more plausible, with gravity "crooking" photons (and makes more sense in the spacetime model, as well as, well, my head's physics engine). And since a photon can't travel at a speed slower than c, I assume that it is simply impossible to emot a photon "away" from a black hole.

 

[twofish-quant]

I've come to understand that there is some reason to believe they pop up here and there at subatomic level, but once again, nothing beyond that.

There really isn't. Thinking of space as some sort of "foam" is one of the ideas that have been proposed to unify general relativity and quantum mechanics. It's really just total guesswork right now.

is there a good reason to believe they actually exist?

There is no reason to believe that they actually exist *BUT* not haven't a good reason for something to exist isn't enough for most theoretical physicists. You have to provide an argument as to why they can't. At this point it becomes a hard problem.

One thing that you have to show is that you don't have causality problems. If you could arrange two wormholes so that you can shoot your grandfather, this would be bad. However, GR is mathematically complicated and no one has proved that you can't do that.

How does a photon react to gravity? I know it's pulled in by black holes, but in what manner? Do they immediately change direction towards the black hole at c, or do they orbit around it ad infinitum, getting closer and closer?

It depends on the direction that the photon travels. If you point a photon in the right direction around a rotating black hole, it will go into orbit. Otherwise, it could get bent or fall in.

And since a photon can't travel at a speed slower than c, I assume that it is simply impossible to emit a photon "away" from a black hole.

It's impossible to emit a photon from a black hole, but Hawking made a name for himself by showing that you can produce photons near the event horizon.

 

[TubbaBlubba]

Ah, I think I understand. As long as you don't violate any laws of physics, you can make up whatever theoretical stuff you want to. Makes sense when you think about it.

Ah yes, Hawking radiation. I've only seen about it on some popular science show once - an elementary particle and an elementary antiparticle emerge, the antiparticle gets pulled in and the positive one escapes, right? What I don't quite understand is... Where does the net energy for the particle/antiparticle pair to emerge come from? Annihilating a pair produces energy, so creating one should require some... Or is the energy "pulled out" of already existing particles at the event horizon? Like, say, a proton passes by, and an elementary antiparticle is pulled from it, emitting a positive particle?

 

[cahill8]

A photon can spontaneously produce an electron-positron pair (see pair production)

 

[Chronos]

I doubt wormholes, as classically portrayed in scifi, actually exist within this universe. I think it would create severe causality problems - not unlike feedback in a speaker system. A wormhole to a parallel universe appears a superficial possibility. I do, however, have concerns about the implications of leaking energy from this universe to another universe.

 

[TubbaBlubba]

I doubt wormholes, as classically portrayed in scifi, actually exist within this universe. I think it would create severe causality problems - not unlike feedback in a speaker system. A wormhole to a parallel universe appears a superficial possibility. I do, however, have concerns about the implications of leaking energy from this universe to another universe.

I remember reading Stephen Hawking's thoughts on wormhole feedback. I believe he thought it'd be a problem when attempting to travel into the past, but not into the future.

 

[Couchyam]

The theory of General relativity basically treats gravity as an inertial force; that is, a "virtual" force not unlike the Coriolis effect or centrifugal force experienced by a rotating body. This is because the gravitational force is proportional to inertial mass. The result of this is that we can treat mass as if it "warps" space, in a way similar to how a rotating reference frame depicts space as being "warped" (if you spin around, you see an object moving in a straight line actually moving in a time-dependent orbit).
This is what causes light to "bend."

With regards to wormholes, the only scenario I can think of is if the "back-ground field" could somehow be altered to include some sort of intermediary "region" associated with two otherwise separated regions (i.e. when entering one of the "normal" regions, you can "move" into the intermediary region or stay in the normal region; after moving to the intermediary region you could then move to the other region). However, light signals could do the same thing, and so you would never actually be outrunning a signal of light. There may be problems though when certain additional constraints are established on space (for instance, imposing a certain limit on a spatial "network" node)

 

[TubbaBlubba]

Yeah, I'm pretty familiar with that concept. Thanks for the elaboration, though.

 

[nismaratwork]

I remember reading Stephen Hawking's thoughts on wormhole feedback. I believe he thought it'd be a problem when attempting to travel into the past, but not into the future.

Specifically, he and Kip Thorne believe that a "time machine" would begin to self destruct due to arbitrarily high energy densities caused by infinite transits of some particles. Feedback seems like a fine way of putting it. If there are many universes, it wouldn't be hard to imagine ones in which wormholes exist, and Closed Time-like Curves exist. That universe would not be familiar to us at all.

Travel to the future, is what we do every day, and has no effect on causality without the capacity to return to your Point of Origin. That doesn't mean that it is possible to travel far into the future in a practical way.

 

[benrot]

in my garden I have loads of wormholes, the birds they love then, the worms.
In the universe if they existed, if we went into one we would instantly be bought back to the initial point so in fact it would take us nowhere,The time is allways going forward materially speaking, we can look back(telescopes) but do we really se what happened, is the image we see has it not been changed by the time, just like and old photo?

 

[HarryRool]

Here are a few relevant entries from this http://www.webfilesuci.org/WormholeFAQ.html":

Have any naturally occurring wormholes been discovered?
No. If they do exist, they are likely to be the result of primordial microscopic wormholes being inflated to macroscopic size during the inflationary phase of the universe’s development.

If no wormholes have ever been discovered, why should we consider them?
The best way to test and extend our theories of nature, especially in the absence of experimental data, is to check their logical consistency in extreme hypothetical cases. This, after all, is how Einstein discovered relativity. Wormholes are examples of such cases. They are predicted by an extremely well tested physical theory, general relativity. If we believe this theory, then we believe that they can exist. If they can exist, and if circumstances conducive to their creation and maintenance have occurred, they do.

How could a macroscopic wormhole arise naturally?
The primordial universe might have spawned, through a process known as “quantum tunneling”, unstable cosmic wormholes that have been expanding along with the universe. If the accelerating expansion of the universe first detected in 1998 is due to cosmic exotic matter, such matter might somehow have expanded the submicroscopic wormholes believed to be contained in the vacuum state of spacetime.

This FAQ is an excerpt from a recent (2010) book on wormholes (https://www.amazon.com/dp/0984150005/?tag=pfamazon01-20)

 

[WannabeNewton]

in my garden I have loads of wormholes, the birds they love then, the worms.
In the universe if they existed, if we went into one we would instantly be bought back to the initial point so in fact it would take us nowhere,The time is allways going forward materially speaking, we can look back(telescopes) but do we really se what happened, is the image we see has it not been changed by the time, just like and old photo?

A wormhole connects two asymptotically flat regions of space - time but these need not be the same regions.