Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Joshua Speelman on 15/12/2010 13:30:03
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Joshua Speelman asked the Naked Scientists:
In science-fiction book and movies, the concept of faster than light travel is often portrayed by "space folding" or "wormholes". Â
Are such things even hypothetically possible or are they just flights of fancy?
Joshua Speelman
Michigan, USA
What do you think?
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Hi, Joshua,
I am not a scientist, but I have a sort of interest in time travel, so I have done a bit of reading on this subject. This extract from my notes may be of interest.
So much has been written about wormholes, both in science fiction and in popular science books that it is very easy to lose sight of the fact that a wormhole is actually a hypothetical topological feature. No-one has ever seen a wormhole, or even found physical evidence of one. Furthermore, although there is good evidence for the curvature of spacetime, in various scenarios, there is no actual physical evidence for the large scale “folding” of space that would permit the use of wormholes as the sort of shortcuts, illustrated in numerous popular science books.
Traversable wormholes are not ruled out by general relativity, and it could be that one of these might occur naturally. However, by far the majority of the solutions of the equations of general relativity indicate that naturally occurring wormholes would be so short lived that their throats would snap shut before even light had time to pass through; so a theoretically traversable wormhole might be of absolutely no practical use, unless it could be modified in some way.
Enter Kip Thorne, who demonstrated that a Lorentzian wormhole could be held open by the introduction of exotic matter – a theoretical substance which has negative energy density, and which may not be ruled out by general relativity.
So, all very hypothetical stuff, but great for science fiction, which I think is where it all started.
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That's a good answer for a non-scientist, Bill.
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Until a wormhole is found, they can only be a hypothetical flight of fancy. The question is, would we recognise one if it were there? Could we actually detect a wormhole, if they do exist?
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Could we actually detect a wormhole, if they do exist?
"Cherchez le ver."
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I don't think there are any stable wormholes. Maybe they can come to be some short instant but they should collapse immediately. the only way to keep one 'open' seems to be if you could 'coat' its 'inside' with something strong enough (a 'force') to stop it from collapsing on itself, I saw some such idea somewhere I'm sure?
Don't remember what they suggested using though, but whatever it was it made no sense as you should be crushed to smithereens trying to travel such a thing anyway.
If you think of how Einstein used the concept of 'geodesics' to present the idea of a 'wrinkled' 'SpaceTime' though :) Expending energy you can break loose from those 'geodesics' light takes and so shorten the journey. ´But looking at space 'naievly' that would not shorten the 'distance' from A to B, as it would seem as the shortest line anyway in a Newtonian 'space', as I understands it.
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Don't remember what they suggested using though
If I remember rightly it was Kip Thorne, responding to a question from Carl Sagan, who started it all. His suggestion that exotic matter could be used to prop open these hypothetical wormholes has been taken up by others since. I think Thorne had grave doubts about the feasibility of all this, so perhaps he is a reluctant hero of the time travel revolution.
One thing that puzzles me is how one would get the exotic matter into (through) the wormhole if it was inclined to snap shut before light had time to pass through, which seems to be the prediction.
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I don't think there are any stable wormholes. Maybe they can come to be some short instant but they should collapse immediately. the only way to keep one 'open' seems to be if you could 'coat' its 'inside' with something strong enough (a 'force') to stop it from collapsing on itself, I saw some such idea somewhere I'm sure?
Don't remember what they suggested using though, but whatever it was it made no sense as you should be crushed to smithereens trying to travel such a thing anyway.
If you think of how Einstein used the concept of 'geodesics' to present the idea of a 'wrinkled' 'SpaceTime' though :) Expending energy you can break loose from those 'geodesics' light takes and so shorten the journey. ´But looking at space 'naievly' that would not shorten the 'distance' from A to B, as it would seem as the shortest line anyway in a Newtonian 'space', as I understands it.
To make a wormhole stable, we require exotic matter... this may come readily in black holes, however, we cannot make much of this in the lab. The closest we come to making this stuff, exists in the center of an interaction in the vacuum called the Casimir Effect.
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To be honest I only know of one kind of matter myself, the one I meet everyday. I can't touch any 'anti matter' as it would transform, together with parts of me presumably, into rest products of positive energy as I understands it :) Exotic matter as seen inside a vacuum may exist, but I would rather call it a 'foam', or a 'fluid', or a 'field' myself. To me matter constitutes of what is 'touch able' by me. The baryonic kind (http://en.wikipedia.org/wiki/Baryon) if you like :) But there exist several definitions of what 'exotic matter' constitutes. (http://en.wikipedia.org/wiki/Exotic_matter)
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Well, exotic matter is just like ordinaty matter except for one fundamental difference, and that is it is an antigravity substance. It's just as real and just as tangible as all other matter. Large amounts of it however are rare.
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Well, exotic matter is just like ordinaty matter except for one fundamental difference, and that is it is an antigravity substance. It's just as real and just as tangible as all other matter. Large amounts of it however are rare.
Has anyone actually found proof of Anti-gravity partials/material? Not so much rare as highly theoretical, surely?
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Well, not to my knowledge. We can theoretically create some of this stuff. A very small portion of the Casimir force an interaction between two plates in a vacuum has a very small amount of exotic matter. So yes, we can make this stuff in the lab; we cannot harvest it though, to any practical needs however.
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I thought the Casimir effect was due to interaction between virtual particles and the metal plates, but it's all a bit technical for me.
Where does the exotic matter come into it?
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I'll try and sum this up quickly then, as lay as I can make it.
The energy arising between two plates in the vacuum is an increasingly negative energy as the plate seperation is reduced.
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Sorry,QC, I still don't see the link between negative energy and exotic matter. [:I]
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I hate to state the obvious, but negative matter is a negative energy -Mc^2.
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So yes, we can make [exotic matter] in the lab; we cannot harvest it though, to any practical needs however.
Wikipedia, the bastion of all human knowledge [;)], says the following about Exotic matter:
"[Exotic matter can be] Hypothetical particles which have "exotic" physical properties that would violate known laws of physics, such as a particle having a negative mass."
http://en.wikipedia.org/wiki/Exotic_matter
It lists other definitions of ExM, but this is the only one that comes close to fitting what you are describing.
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QC - you're making a lot of leaps there. Casimir effect is not normally viewed as proof of either negative energy nor negative mass which as p'corn (1,000 post congratulations) mentioned is still highly theoretical and thus fits the name exotic. Casimir is generally seen as the ruling of out of larger wavelength sections of zero point energy fluctuations; thus causing an imbalance and an inward force. There is a great demonstration here at Wolfram (http://demonstrations.wolfram.com/TheCasimirEffect/) and a really good 'layman's' (some peoples favourite term of opprobruim at the moment) explanation here at IOP (sign up required - but free) (http://physicsworld.com/cws/article/print/9747)
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Let's take a look shall we at what I said. If we go to wikipedia's article on the casimir effect, we actually have a small portion dedicated to wormholes:
''Exotic matter with negative energy density may be required to stabilize a wormhole.[20] Morris, Thorne and Yurtsever pointed out that the quantum mechanics of the Casimir effect can be used to produce a locally mass-negative region of space-time,[21]''
Which is what I have said.
http://en.wikipedia.org/wiki/Casimir_effect
The idea the energy is increasingly negative is not actually theoretical - it's a part of experimental fact. It is used in the hopeful harvest of large amounts of negative energy http://arxiv.org/ftp/physics/papers/0010/0010027.pdf
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QC - I hate to quibble on an off-topic note, but that is one unpublished paper and an aside on wikipedia. I am not even saying you are incorrect - but need a little more backup than that for such statements as
It's just as real and just as tangible as all other matter
it's a part of experimental fact
So yes, we can make this stuff in the lab
I would love to see the Nature/Science article (cos it would be in one of the real biggies)
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You have a quibble with the statement that exotic matter is just as tangible as ordinary matter??
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Just testing something c2 p2
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I hate to state the obvious, but negative matter is a negative energy -Mc^2
It may be obvious to you, but some of us oldies take a while to catch up. I think I'm getting there,slowly. [:-\]
Presumably you would have to do something to negative matter to convert it to negative energy; sort of "negative", nuclear reaction.
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An example of negative matter is imaginary mass. In a sense, there is nothing in the mathematics in general which tells us imaginary matter or even negative rest energy should not be tangible like ordinary matter. Imaginary matter has a mass M which also has an imaginary value at M2<0. The observable mass of these particles exists as E=gM, and is real and positive. The force enters the equation as Fg=-▼φMg.
The negative matter particles and even particles with a negative matter and an imaginary mass obey the equation E2=M2+p2. This means it has your usual rest mass M0. For tachyons, this means the energy has an usual property as E2=p2-|M2|. There is nothing in the equations which suggests that the mass is not real (not in the mathematical sense) or tangible, since we have regular rest masses.
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Don't they have some in Wimbledon?
Oh! I'm terribly sorry. I will have to get new specs. I thought this thread was about wombles.
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QC - so is that a 'no' you can't/won't provide any good references?
Just going by Wikipedia - I note that my view is not controversial. I am just wondering how you can be so certain - you seem to be equating mathematically hypothetical exotic matter with the merely very unusual (like a bose-einstein condensate). The BE-cond is a good example of what I am asking - are you stating that matter with negative mass is like the BE-condensate, ie has been shown to be mathematically consistent and will be found when the circumstances can be duplicated, or that is it merely a theoretical construct? Frankly neither of the above tally with your remarks about these substances existing in labs, being real and tangible, and experimental fact
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Did I ever say ''no''?
I asked you if ''do you really find the tangibility of negative matter different to ordinary matter?''
I found your objection to this, interesting and surprising.
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As it is, I am looking for references. References on the negative energy of the casimir effect is not well-documented on the net.
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I knew I wasn't imagining this stuff up;
''Casimir effect and propulsion
The Casimir effect has been linked to the possibility of faster-than-light travel because of the fact that the region inside a Casimir cavity has negative energy density.''
http://www.daviddarling.info/encyclopedia/C/Casimir.html
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''
One of the more interesting aspects of A and W plot of fig [1] are the convoluted shapes of the constant energy curves especially in the negative energy region.''
http://www.fdscience.org/1/aiaa983140.pdf
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I asked you if ''do you really find the tangibility of negative matter different to ordinary matter?''
I found your objection to this, interesting and surprising.
Tangible means real, concrete, and touchable; something that only exists as a hypothetical construct is not tangible. This back-and-forth started when it was discussed where the exotic matter needed to keep only a wormhole in Kip Thorne's idea would come from, and you said inter alia "however, we cannot make much of this in the lab" You have said on other occasions that it is experimental fact and real/tangible. So far all I have seen is a mathematical interpretation of the casimir and two non-peer reviewed papers. I understand mass energy equivalence, but I cannot leap from imbalances in the quantised zpe to the physical existence of negative mass matter. I am trying to get hold of the Ambjorn Wolfram paper to read but with no success.
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Of course you can touch negative matter, if it existed... It is a dynamical quality which theory uses to thread wormholes with to keep them open. How more tangible do you need the matter to be?
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Matter interacts with matter, depending on what forces that matter interacts with. As you will see from my links, this is not a matter of it being hypothetical. It is a matter of experimental fact - there is a region within the cavity of the casimir effect which exhibits what we would call a negative energy. It's very very small, but it does exist within the theory, and if theory is correct, we have been making this stuff for a while.
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QC I think I will give up - how much more tangible do I need matter to be? For it to be tangible it must exist! Nothing you have provided convinces me that you are not extrapolating like crazy.
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Around 70% of the energy in the universe is negative and is making the universe expand faster than light. How much more tangibility do you need?
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Now you are grasping at straws - the universal expansion is possibly due to a cosmological constant or otherwise due to unknown "dark energy"; it is an open question at the moment, but it is certainly not been determined as negative-mass matter. dark energy as a cosmological constant is a constant energy density / vacuum energy throughout space - it is certainly not negative energy. dark energy as some "as yet unknown" scalar field, is "as yet unknown" and is proof of nothing.
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Excuse me, but you play these pedantic word games, then you accuse me of clutching onto straws when I mention the tangibility of negative matter in the universe platying a role in the accelerated expansion? If you won't believe my words on the casimir effect having a small negative region of energy, then you surely cannot sustain a healthy arguement against something so mainstream as a negative energy density taking about 70% out of all matter in the universe surely?
You are arguing that negative matter cannot be touched and is not tangible. If in the sense you want some to touch, then by all means, you will most probably die before such a revelation occurs. However, if you can accept the theoretical side of things, no matter how tenebrous the idea may seem to you, some of us believe in quantum field theory, and the predictions of negative matter existing ''tangibly'' in the vacuum itself. We do afterall, have over a decades worth of proof on the subject contrary to what you may wish to believe in.
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Oh and yes, all good scientists within the mainstream believe the matter and energy must be negative, or it would not be making the universe accelerate, by the way.
You accuse me of not sticking to mainstream, but you do a bad job of it youself.
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There is nothing in the equations which suggests that the mass is not real (not in the mathematical sense)
Is this another case of mathematical "reality" not necessarily being the same as physical reality?
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There is nothing in the equations which suggests that the mass is not real (not in the mathematical sense)
Is this another case of mathematical "reality" not necessarily being the same as physical reality?
:)
I just like to make sure no one gets mixed up with real and imaginary quantities, and in the case above, I meant real as neither the mathematical quantity, but in normal language. Because we have been discussing exotic matter, and even tachyons, imaginary (or complex) quantities can and usually do crop up.
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And it would be well noting, that the mathematical term ''imnaginary'' is just as real as the real number system, and represents quantities which are also just as real as the real system describing everyday objects; this is one reason it should be noted that imaginary matter, or even negative mass should have tangible qualities just like ordinary matter. Nothing in the equations state they aren't.
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Well mathematically there exist a theorem like something over a hundred years old that I read about a long time ago, proving that parallel lines always will meet in the end. Mathematically impeccable it is too :)
So the question becomes, don't we need something more than just mathematics to prove it existing here with us?
I think we do, that's why the math we trust will have some experimental verification. doesn't mean we don't trust the other kind too :) But it may at times belong to some other universe, possibly?
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Yes, but that is why we have experimentation as well as mathematics to catalogue our events.
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I am out of this discussion - you have still to provide a single article to back up your claims. Your arguments are becoming increasingly nonsensical.
A. There is no consensus on dark energy
B. Dark Energy is not negative energy - it is negative pressure
I am quite happy with strange and exotic theoretical predictions - but you are describing them as mainstream and concrete. Secondly, you have started to call everyone who disagrees with you asinine and now I am "playing pedantic word games"; frankly I cannot be bothered with someone who knows little and disguise this fact by using repeated fallacious arguments and insults.
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Good, I've had enough of you too. You were playing pedantic word games. I said in theory, negative matter would be tangible, you disagreed. I said what proof you had. You said if it doesn't exist then it isn't tangible. How is that not word games?