Wormholes Unstable (BBC)

An anonymous reader writes that "The BBC reports on recent theoretical physics research showing that wormholes may not be very useful for space or time travel. Wormholes with smooth or classical spacetimes appear to be unstable and fall apart quickly. Too bad for budding time travelers and space explorers!"

Comments

All you need is PART of the wormhole

[Vitriol Angst]

The wormhole doesn't have to be stable to be useful. You could create a wormhole around a ship, and allow it to break apart behind. You could also say that rockets are unstable, because they only have a stable stream of plasma for a few feet--yet they still move the rocket.

Of course, putting limits on things that are still fiction is kind of ironic.

Actually, it's likely much more

[jd]

I did a simple, back-of-the-envelope calculation on what it would take to keep a wormhole open.

You need to have a net negative mass, which means that your exotic matter (or energy equiv) must be equal to the mass of the object traversing the wormhole, PLUS the mass of the wormhole itself, PLUS the mass of any other particles within the wormhole, PLUS the mass equiv of the energy that the vaccuum created naturally has.

You also need to bear in mind that exotic matter is believed to have a very short half-life - about 10^-30 seconds - which means that it must be traversing the wormhole at high speed and must constantly be replaced at that rate.

But that isn't all! There is a problem with wormholes in close proximity to each other - they are unstable. And quantum-scale wormholes supposedly occur everywhere in the quantum vaccuum. So, you've got to do some fairly complex stuff to exclude other wormholes from the vicinity of the one you want.

Generating the exotic matter/energy is also a hard problem. Methods include the Casmir Effect, which requires generating fields of absolutely staggering strength to exclude all possible positive energy between two plates. The exclusion principle, combined with the requirement that a vaccuum must have a non-zero state in QM, is what forces the existance of a negative state.

So, what you need to do is basically have gigantic Casmir Effect-based exotic matter generators, which will require vastly more positive energy then the negative energy they create.

I think I figured out that you'd need to convert most of the galaxy into pure energy in order to move even a relatively small object via a wormhole over any kind of reasonable distance, once you take these additional requirements into account.

The problem is, if you are capable of collecting a galaxy together to convert it into enough energy to do this, you have sufficient technology to reach anywhere in the galaxy anyway, making the wormhole method of travel totally unnecessary. Besides which, you also get the benefit of having somewhere to go.

"Negative Energy" a conceptual mistake?

[Pfhorrest]

This isn't exactly a response to your post, but more a question for this entire thread... but you seem like you may be a physicist or at least well versed enough in the mathematics thereof to be able to do "back-of-the-envelope calculations" about it, so maybe you can answer this question for me.

Why is it assumed that because something has negative mass - which I would define as "the quality of being repelled from, rather than attracted to, ordinary positive mass" - it has negative *energy*? Likewise, why is it assumed that any energy (such as vacuum energy) translates directly into positive mass?

I've always viewed it similarly to charge. Both mass and charge are a form of potential energy. An electron and a proton have the same amount of electrical potential energy as one another, only differing in the nature of that potential relative to other charges (whether it repels or attracts a positive or negative charge). But does a proton then have "positive" potential energy and an electron have "negative" potential energy? If the answer to that is no, then why does something with "negative" mass have to have "negative" energy? Is a space filled with a negative charge "less than empty vacuum"?

I'm well aware of e=mc^2 of course, and why that would lead to a negative value for e if you have a negative value for m. But given that physics traditionally deals with only positive values for m, wouldn't e=|m|c^2 (using the absolute value of m, instead of just m) return the same results for all physics thus far, dealing with positive mass, without the counterintuitive "less than nothing" idea of "negative energy" if ever we managed to produce something with negative mass?

Re:"Negative Energy" a conceptual mistake?

[Pfhorrest]

That was an intelligent answer, but I think you may have misunderstood the nature of my question, and as such have not entirely answered it.

I was not claiming that a negative charge was negative energy, or asking for clarification about that. I was analogizing the potential energy due to charge (electrostatic force) with the potential energy of a mass (gravity). An electron and proton, ignoring gravity, have a certain amount of potential energy relative to one another just because of their charges; that is to say, if released, they would move closer together and gain velocity, and kinetic energy. A hypothetical particle identical to an electron but with a greater charge would have *more* potential energy relative to that proton, as the attraction between them would be stronger, even though their masses are the same, so it's pretty clear that the attraction due to charge counts as "potential energy" the same as attraction due to mass.

But now, take the potential energy due to charge (again, ignoring gravity) of two electrons. As the charge of a proton and and an electron are equal but opposite, is the potential energy between them (ignoring gravity) not the same? Or would you say an electron has a negative potential energy (even considering gravity now) to another electron, since they would repel one another? In that case, the "positive" and "negative" differences of energy seem only to apply to potential, not kinetic, energy, and refer only to the direction of the force applied relative to another body.

Furthermore, in the case of electrical charges, that attraction or repulsion is relative to not only the strength but the sign of charge of another body, in which case, how do you know that this exotic matter with negative mass, while it may have negative (repulsive) potential energy to positive mass, does not have positive (attractive) potential energy to other exotic matter? After all, we know that likes attract with positive masses, so it stands to reason that likes would attract with negative masses as well.

Has anyone ever made or discovered particles of this "exotic matter" and measured the relative attraction of them to each other? I imagine for the extremely short lifespans you claim for it, it would be difficult to do such an experiment, especially here amongst all this positive mass, and especially to isolate the effects of gravity from electric and nuclear forces.

This is a common area that seems conceptually vague amongst every physicist I've personally spoken with and most of the ones I've read. Einstein seemed to clarify it best in his personal layman's version of relativity. People speak of the "size" of particles, and of "matter", as nebulous concepts separate from the force-fields which define the characteristics of those particles. For example, when pressed to define "volume" as an independent quality of a particle, as when people say "atoms are mostly empty space", most people, even physics professors, I speak to fail to give any definition.

Is it the size of an atom the radius of its outermost valence level? By that definition the entireity of space inside that valence shell IS the atom and is therefore not empty. So, scratch that idea, the space of the atom is only filled by the particles it's made out of and the rest is empty. Ok - what's the volume of an electron, or a proton? It's not clear how that should be defined - by it's mass? By its charge? How do you measure volume in units of mass or charge? Do you measure the volume by the extent that the strong nuclear force keeps other particles (of regular, non-antimatter at least) from overlapping that pointin space?

What is the extend or nature of something devoid of any of its force-fields? Can you run into an empty shell with no mass, charge, or nuclear forces? What exactly would you be running into? People say atoms are mostly empty space - I say everything is nothing but space, and none of it is empty.

From recollection, Einstein spoke in his laymen's book on relativity about an a c