Is reverse time dilation posssible?

LodeRunner
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Hypothetically, if someone built an antigravity generator out of an exotic material that warped spacetime in an opposite way, so that matter was repelled instead of attracted, would the passage of time speed up for that frame of reference?

I'm not a physicist or physics student, though I am a sci-fi writer interested in being as realistic as possible. It occurs to me that if negative energy densities and exotic matter do exist and have inverse gravitational properties, then inverse time dilation must also be a possibility. Given an antigravity generator of sufficient power, one could achieve impressive effects, ex. speeding up the passage of time in a certain region of space so much that for every second that passes outside the region, many years pass on the inside.

Of course, the strong antigravity would make it very difficult for anyone to remain in this region of space for long, but I think I've already figured out a way around this problem. Given a spherical net of antigravity generators connected by filaments made out of another fantastic and nigh-unbreakable form of matter, the region of space at the center of the sphere should experience accelerated time without any harmful effects. The generators would be positioned so that they would cancel each other out, i.e. each object in the region is subjected to very strong antigravity, but from all sides equally. My first instinct was to assume that the objects in the center would be crushed into neutronium, but then I realized that this could only happen due to tidal gravity. If the central region is proportionally small enough (as compared to the entire volume of the sphere) that the strength of antigravity is roughly the same from every direction at every point in the region, then objects or people located in that region of space would feel no gravity at all... yet they would experience the reverse time dilation, because that would not be canceled out.

Comments and objections are very much welcome. I consider myself reasonably well read in relativity and physics, but I wouldn't mind hearing from someone who really knows what they're talking about. Given the existence of these antigravity generators and a cable with incredible tensile strength to keep them from flying apart, would this device really work?
 
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Time dilation doesn't speed up or slow down time for a given frame of reference, it is what you get when you compare two frames. So to slow your time compared to someone else, move with respect to the other frame. And to speed up your time compared to someone else, have them move with respect to you.

Most of the rest of that is just idle speculation.
 
russ_watters said:
Time dilation doesn't speed up or slow down time for a given frame of reference, it is what you get when you compare two frames. So to slow your time compared to someone else, move with respect to the other frame. And to speed up your time compared to someone else, have them move with respect to you.

I know that it's only valid when comparing two frames of references, but for sake of brevity one can often shorten it to "it slows down" (or in this case, "it speeds up") time. In the real world there will always been another frame of reference to compare it to.

...move with respect to...

Um, I don't mean to be condescending, but you are aware of the existence of gravitational time dilation, right? That time slows down considerably as one enters a region of space containing a black hole? (Again, this is just shorthand for "as compared to a frame of reference outside of this region of space and outside the influence of any other black holes")

I am not really concerned with velocity time dilation at the moment, and your bringing it up makes me suspect that you are wholly unaware of gravitational time dilation.

Most of the rest of that is just idle speculation.

Speculation, yes, but I take offense at the "idle". Like I said before, I am an aspiring science fiction author; it's my duty to speculate. However, there is a marked difference between wild Star Trek-type speculation made solely for the purpose of advancing the plot, and speculation that is at least somewhat grounded in reality, and could even conceivably lead to an actual scientific theory (emphasis on "could".) I believe that this speculation is the latter, though I'm not yet sure.

There ARE such things as negative energy densities. The Casimir Effect is the only proved example that I know of, but its existence at least makes it plausible that other forms of exotic energy or matter could exist. Given that gravitation increases with mass, a negative mass (to me) implies negative gravitation, which implies negative time dilation.

There are numerous problems with the actual implementation of my idea, but I am concerned only with theory. In a sci fi story, one does not need to know how exactly every single widget works; I just want to know if it is plausible.

So, I'll ask again: Does negative mass imply negative gravitation, and if so does that then imply negative time dilation (speeding up as compared to other frames of reference that lack a source of anti-gravity)?
 
russ_watters said:
Time dilation doesn't speed up or slow down time for a given frame of reference, it is what you get when you compare two frames. So to slow your time compared to someone else, move with respect to the other frame. And to speed up your time compared to someone else, have them move with respect to you.
I think LodeRunner was talking about gravitational time dilation, not velocity-based time dilation as seen in inertial frames. Gravitational time dilation is more "objective" in the sense that both observers will agree whose clock is running slower, in terms of what they see using light signals (and I think they'd also agree about whose clock was running slower relative to some 'natural' choice of coordinate systems, like Schwarzschild coordinates). I don't know what would happen if you plug in negative mass/energy into the equations of general relativity (I know you don't get complete nonsense, negative energy is part of the recipe for stable wormholes in GR)--does it lead to any sort of "antigravity"? In Newtonian physics, if you place a negative mass next to a postive one, the positive one is gravitationally repelled by the negative one, while the negative one is gravitationally attracted to the positive one, so something similar should be true in GR. Would the time dilation effects for observers at different distances from a negative-mass planet be the same as if it had positive mass?
 
Traveling forward in time is easy and automatic in this universe. You can adjust your speed of time [relative to the clocks of your target object] by accelerating in it's direction. This will cause your clock to run slower than the target clock. Gravity is the fundamental player here. Gravity is attractive for both matter and anti-matter, but theoretically repulsive for imaginary matter. If you can figure out how to make imaginary matter, you might be able to travel back in time [and most likely lose causal contact with everything in this universe].
 
The biggest unrealistic story element from the standpoint of pure physics are the anti-gravity genreators (in my opinion, anyway).

If you postulate a negative-mass Schwarzschld solution, it should generate gravitational time acceleration as you suggest. If you make the negative-mass Schwarzschild solution hollow, it should have a field-free region in the interior, as you suggest. In order to get significant time accelerations, though, you would need to generate a black hole-sized negative mass (the amount of mass required depends on the radius you want to enclose in the time acceleration field) AND you'd have to hold it together. This would not be actually practical, but I don't think there's anything wrong with the theory.

This would be one way of meeting a tight schedule at work, though perhaps a trifle expensive :-).
 
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Chronos said:
Traveling forward in time is easy and automatic in this universe. You can adjust your speed of time [relative to the clocks of your target object] by accelerating in it's direction. This will cause your clock to run slower than the target clock. Gravity is the fundamental player here. Gravity is attractive for both matter and anti-matter, but theoretically repulsive for imaginary matter. If you can figure out how to make imaginary matter, you might be able to travel back in time [and most likely lose causal contact with everything in this universe].
I don't know if LodeRunner was talking about going backwards in time, I thought he/she was asking if clocks would speed up relative to distant observers when they got close to a negative-mass object, the way they slow down relative to distant observers when they get near a positive-mass object. If I'm understanding pervect's answer correctly, the answer is yes.
 
pervect said:
The biggest unrealistic story element from the standpoint of pure physics are the anti-gravity genreators (in my opinion, anyway).

I pretty much knew this would be the case from the outset, but I'm quite content with it being theoretically possible, even if it is in all probability impossible to construct. It's a big stretch of the imagination to think that a civilization would ever overcome these technical hurdles, even an very highly advanced civilization, but I think sci-fi was meant to stretch our imaginations. At least this contraption has its theoretical roots based in science fact, which is something you can't say about many of the devices and phenomina found in pop sci-fi.

Many thanks for the replies. I may return later...I've got this idea for an ultimate weapon that I've been toying with...
 
JesseM said:
I don't know if LodeRunner was talking about going backwards in time, I thought he/she was asking if clocks would speed up relative to distant observers when they got close to a negative-mass object, the way they slow down relative to distant observers when they get near a positive-mass object. If I'm understanding pervect's answer correctly, the answer is yes.

You're quite right of course, but I think Chronos may also be right in saying that negative mass or energy is a key component in being able to travel back in time. I seem to remember Hawking saying that he had mathematically proved this in one of his books, that one needed negative energy (or mass) in order to travel back in time.
 
  • #10
LodeRunner said:
You're quite right of course, but I think Chronos may also be right in saying that negative mass or energy is a key component in being able to travel back in time. I seem to remember Hawking saying that he had mathematically proved this in one of his books, that one needed negative energy (or mass) in order to travel back in time.
Negative energy is a key component in propping a wormhole open, and wormholes could theoretically be used for time travel by moving one mouth at high velocity away from and back towards the other mouth, so the mouth taken on this trip will be "younger" when it returns, like in the twin paradox. But if you looked through the wormhole from one mouth to another during this trip you'd see clocks near both mouths ticking at the same rate, so that time is threaded differently through the wormhole than through normal space--if we are both 30 years old when you depart with one mouth while I stay with the other one, and the trip away and back takes 5 years for you but 10 years for me, then when you return you will meet me as a 40-year old, but if you jump through your mouth you will pop out of my mouth when I was only 35 years old. It's possible that quantum effects will conspire to destroy the wormhole when one mouth enters the other's light cone though (which would be the point where time travel would become possible), and I think it's also not known if negative energy is really possible (it's true that the casimir effect shows you can have energy that's lower than the ground state of the quantum vacuum, but without a theory of quantum gravity I don't think physicists can say for sure that this has the same meaning as negative energy in GR, or if the quantum vacuum should be thought of as having some nonzero energy of its own).
 
  • #11
JesseM said:
In Newtonian physics, if you place a negative mass next to a postive one, the positive one is gravitationally repelled by the negative one, while the negative one is gravitationally attracted to the positive one, so something similar should be true in GR.

How does that work exactly? Does anyone know if it holds up in GR?

I didn't count on the antimass actually being attracted to matter at the same time that the matter is being repelled. Do the repulsion and attraction cancel each other out exactly? Are they dependant on mass/antimass? Does the antimass repell other antimasses? Would the sphere implode on itself under the attraction of the +mass or be halted by its own repulsion of itself or halted by the repulsion of the +mass? Is any of this at all answerable, theoretically speaking?
 
  • #12
Note that an object with negative mass near another object with poisitive mass would experience a repelling force due to its negative gravitational mass, but would accelerate towards the positive mass due to its negative inertial mass (assuming the validity of the equivalence principle). On the contrary, the positive mass would experience also a repelling force but would accelerate away from the negative mass.
 
  • #13
LodeRunner said:
Um, I don't mean to be condescending, but you are aware of the existence of gravitational time dilation, right?
Yeah, sorry - the same thing can be achieved by having different people move up or down in a gravitational field.
 
  • #14
I wonder if the assumption that negative gravity will lead to an acceleration of time is logically making sense at all. Think of the time dilation as being a result of the curvature of space-time, regardless of the 'direction' in which this space-time is curved. Total absense of such curvature, i.e. an absolute flat space-time (like in SR) gives the lowest time-dilation, or you could say that this gives timespeed X. Any curvature, caused by gravity or anti-gravity will then lead to timespeeds <X.
Expecting time to speed up with anti-gravity is a bit like expecting that a 'negative' detour will give you a shorter path.
 
  • #15
I think Mortimer has a point. Picture space-time as the classic rubber sheet. if you drop a bowling ball in the middle the sheet will bend down, representing gravity caused by a large body of mass. Likewise we can picture this body of imaginary mass as a bowling ball being shoved up from underneath the sheet, resulting in everything rolling off of it, or "anti-gravity". But either way, the sheet bending down or up, it will take longer for a lightbeam to traverse that area of space due to the warping of the space-time fabric.
 
  • #16
Reverse time - already been observed.

LodeRunner said:
Hypothetically, if someone built an antigravity generator out of ... experience the reverse time dilation, ...
Experiments have already shown time moving backwards no negative mass or energy required. So “reverse time dilation” real yes, but the “antigravity generator” part I don’t thing so -- but you can make up anything in sci-fi.

If you’d like to demonstrate it mathematically plot out ALL the times distances and synchronizations points for two near light speed ‘trains’. One coming towards your base station and one away from you, both passing several base framed stations along the way. (Take your time and be careful with the conversions and charting the observed times for train cars & stations for all). You should find that apparently one of the trains is moving backwards in time.

Can this be proven? I’d say it already has been! No need to spend Mega Bucks to get a couple of near light speed ships flying. Smaller distances and shorter time intervals have already worked in tests at a much lower costs. Just a couple feet with times under nano-seconds, was all that they needed using Particle accelerators. There you find electrons better understood as positrons move backwards in time, plus positrons better explained as electrons moving backwards in time.

For more details on how this has already been observed and explained see some of Richard Feynman’s lectures on Feynman diagrams. Your term of “reverse time dilation” might not be used but “backwards in time” amounts to the same thing.

But for use in sci-fi writing – frankly your better off just “assuming” something like a “Flux Capacitor” if your intent on going back to meet yourself in the past.
Don’t expect a realistic explanation help make a plot believable. Your story has to do the job of getting the reader/audience to ‘suspend their disbelief’.
 
  • #17
RandallB said:
Experiments have already shown time moving backwards no negative mass or energy required. So “reverse time dilation” real yes, but the “antigravity generator” part I don’t thing so -- but you can make up anything in sci-fi.
If you’d like to demonstrate it mathematically plot out ALL the times distances and synchronizations points for two near light speed ‘trains’. One coming towards your base station and one away from you, both passing several base framed stations along the way. (Take your time and be careful with the conversions and charting the observed times for train cars & stations for all). You should find that apparently one of the trains is moving backwards in time.
Can this be proven? I’d say it already has been! No need to spend Mega Bucks to get a couple of near light speed ships flying. Smaller distances and shorter time intervals have already worked in tests at a much lower costs. Just a couple feet with times under nano-seconds, was all that they needed using Particle accelerators. There you find electrons better understood as positrons move backwards in time, plus positrons better explained as electrons moving backwards in time.
For more details on how this has already been observed and explained see some of Richard Feynman’s lectures on Feynman diagrams. Your term of “reverse time dilation” might not be used but “backwards in time” amounts to the same thing.
Feynman's theories aren't really about time moving backwards in a literal sense. They just show that mathematically a positron moving forward in time can be treated as equivalent to an electron moving backward in time, and likewise an electron moving forward in time can be treated as equivalent to a positron moving backward in time--there is no absolute truth about whether a given particle is moving forward or backward in time. Also, I think "moving forward/backward in time" here is just a verbal description of some mathematical procedure, like whether you evaluate an integral from t_0 to t_1 or from t_1 to t_0. This FAQ on virtual particles says:
Now, consider a virtual photon that comes from the particle on the right and is absorbed by the particle on the left. Actually calculating the photon's wave function is a little hairy; I have to consider the possibility that the photon was emitted by the other particle at any prior time. (However, I can save myself a little effort later by automatically including the possibility that the photon actually comes from the particle on the left and is absorbed by the particle on the right, with the recoil nudging the left particle: all I have to do is include situations in which the photon is "emitted on the right" in the future and goes "backward in time," and take its momentum to be minus what it really is! As long as I remember what's really going on, this trick is formally OK and saves a lot of trouble; it was introduced by Richard Feynman.)
And here's a Feynman quote from a response to a letter someone sent asking about time travel (found on p. 300 of Perfectly Reasonable Deviations from the Beaten Track):
Dear David:

I was glad to hear from you. I looked at your enclosure "Travelling in Time," but didn't read beyond the second sentence because I, also, believe that time travel cannot be done, and I thought my colleagues agreed with me. The science fiction writers who have interpreted my view of the positron as an electron going backward in time have not realized that that theory is completely consistent with causality principles, and in no way implies that we can travel backward in time.


Richard P. Feynman
 
  • #18
I never said Feynman claimed "backwards in time" for the macro world.
Feynman Diagrams are about the micro world. Without accepting backwards time movement inside a Feynman diagram; you’re forced to accept photons appearing from nowhere or being guided to just the right location by Magic.
So I guess you can pick one: Magic Photons or Backwards Time inside the diagram.

If you’re just writing fiction what’s it matter? Otherwise, if you like work though a few Feynman Diagram plots and see what you think. Myself “Occam's Razor” suggests to me that (Within the space-time allowed for the micro experiment) “Backwards Time” is most likely real vs. “Magic Photons”.
 
  • #19
JesseM said:
In Newtonian physics, if you place a negative mass next to a postive one, the positive one is gravitationally repelled by the negative one, while the negative one is gravitationally attracted to the positive one, so something similar should be true in GR.
LodeRunner said:
How does that work exactly? Does anyone know if it holds up in GR?
In Newtonian physics, it's just based on the equation for the gravitational force between two objects with masses m_1 and m_2, F = G m_1 m_2 / r^2 along with F = ma for each object. This means that each object will experience acceleration G m&#039; / r^2 along the vector pointing at the other object, where m' is the mass of the other object. For the positive-mass object, m' is negative, so it experiences the acceleration in the opposite direction as normal gravitational attraction. For the negative-mass object, m' is positive, so it is attracted to the other object in the normal way. This means that if you put two objects of equal and opposite mass next to each other, they will both accelerate continually in the direction of a vector from the negative-mass object to the positive-mass object, maintaining a constant distance between them while their speed increases without bound...this doesn't violate conservation of energy though, because the ever-increasing positive kinetic energy of the positive mass is balanced out by the ever-increasing negative kinetic energy of the negative one.
 
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  • #20
RandallB said:
I never said Feynman claimed "backwards in time" for the macro world.
Feynman Diagrams are about the micro world. Without accepting backwards time movement inside a Feynman diagram; you’re forced to accept photons appearing from nowhere or being guided to just the right location by Magic.
So I guess you can pick one: Magic Photons or Backwards Time inside the diagram.
Particles in feynman diagrams appear from nowhere regardless--if you have a photon that's emitted and absorbed within the diagram, how does the backwards-in-time idea help you avoid it?

And again, I don't think it's really about saying that any given particle in the diagram is objectively moving back in time, it's about having two equally valid ways of describing any given particle, as either a certain particle moving forward in time or its antiparticle moving backward in time.

Also, what did you mean when you said "Experiments have already shown time moving backwards no negative mass or energy required"? What experiments have shown this? The virtual particles in Feynman diagrams are never observed experimentally, they're just part of a mathematical procedure for calculating the probability of various results.
 
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  • #21
nemosum said:
I think Mortimer has a point. Picture space-time as the classic rubber sheet. if you drop a bowling ball in the middle the sheet will bend down, representing gravity caused by a large body of mass. Likewise we can picture this body of imaginary mass as a bowling ball being shoved up from underneath the sheet, resulting in everything rolling off of it, or "anti-gravity". But either way, the sheet bending down or up, it will take longer for a lightbeam to traverse that area of space due to the warping of the space-time fabric.
I think you're taking the rubber-sheet metaphor too literally--the orientation of the curved sheet in the higher-dimensional embedding space (a depression pointing 'down' vs. a bump pointing 'up') isn't relevant, it's only the curvature that matters. Also, although on an ordinary curved 2D surface a geodesic would be the shortest path between two points on the surface, in GR a geodesic is the path through curved spacetime with the greatest proper time (time as measured by a clock that travels along the path), which is not captured by the rubber-sheet metaphor. I don't know the details, but I assume when you do the math, negative energy would curve spacetime in a different way from positive energy...stable wormholes are said to require negative energy to hold them open, which wouldn't make sense if negative energy and positive energy curved spacetime in just the same way.
 
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  • #22
JesseM said:
I think you're taking the rubber-sheet metaphor too literally.
That makes sense, but then where does all this negative mass stuff come from? Not anti-matter I hope, it's mass warps space-time (or the rubber-sheet) the same way as "normal" matter so are you just making something up for the fiction guys here or are you basing "negative mass" [repeling but following + mass ??] on something?
 
  • #23
RandallB said:
That makes sense, but then where does all this negative mass stuff come from? Not anti-matter I hope, it's mass warps space-time (or the rubber-sheet) the same way as "normal" matter so are you just making something up for the fiction guys here or are you basing "negative mass" [repeling but following + mass ??] on something?

Hermann Bondi, "Negative Mass in General Relativity", Reviews of Modern Physics 29, 423 (1957)

is probably one of the first references in physics.

(This is actually a secondary reference from one of Cramer's Alternate View columns, BTW)

http://www.npl.washington.edu/AV/altvw14.html

Negative mass aka exotic matter is also one of the main requirements to build wormholes. The Casimir effect, a force between a pair of _uncharged_ conducting plates in a vacuum, is an example showing that such negative energy densities are not entirely theoretical and may have some physical basis. Note that the Casimir effect is a quantum effect, while GR is a classical theory.

The wikipedia article on exotic matter isn't very good (I seem to recall it used to be shorter and better). The best article I could find on a popular level was

http://www.physics.hku.hk/~tboyce/sf/topics/wormhole/wormhole.html

So far I haven't been able to find anything that refershes my recolleciton on the tie-in between exotic matter and violations of the strong, weak, null, or dominant energy conditions in GR. Basically, I recall that exotic matter and the Casimir effect both violate one of these energy condtions, but not which one it is. Pinning this relationship down, along with an exact statement of the associated energy condition, would make my article a lot less hand-wavy that it has been, but I just can't recall the details anymore :-(.

I thought Cramer had something along these lines in his pop-sci articles about wormholes, but I didn't find anything.

BTW, Cramer's complete collection of old pop-sci articles (not including the last few years) can be found online at

http://www.npl.washington.edu/AV/
 
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  • #24
pervect said:
Hermann Bondi, .. Negative mass aka exotic matter .../QUOTE]Matter and anti-matter vs. exotic matter and I assume anti-exotic matter; OK sounds like good stuff for our fiction writer.

For me, I’ll stick with Occam, since I’m not buying into the “Wormhole” thing anyway.
And if believing the “Backwards Time” is a real thing within a closed microscopic sample, means I consider Anti-gravity, Wormholes and Exotic matter to be fabrications. –-– I’ll take my chances with the negative time till someone can demonstrate one of the others as real.
 
  • #25
RandallB said:
And if believing the “Backwards Time” is a real thing within a closed microscopic sample, means I consider Anti-gravity, Wormholes and Exotic matter to be fabrications.
What does Feynman's backwards-time idea have to do with the question of negative energy in GR? The question of whether or not the second is possible doesn't really have anything to do with whether you accept Feynman's idea (and I don't think anyone disagrees that mathematically Feynman's trick works, whether you interpret this as meaning that some particles are 'really' moving backwards in time seems like more of a philosophical issue).
 
  • #26
JesseM said:
What does Feynman's backwards-time idea have to do with the question of negative energy in GR?
Are you following along in the thread here?? Negative mass (- energy) was brought up as a means of backwards time travel. I’d only pointed out where backwards time had been found for real.
At least in my opinion that has been shown as real in real measurements. Then that contrasts with several declarations that Anti-gravity, Wormholes and Exotic matter should be taken seriously with nothing real to back them up.

As to realistic as possible fiction writing, I don’t think the philosophical issue arguments will help much.
 
  • #27
RandallB said:
Are you following along in the thread here?? Negative mass (- energy) was brought up as a means of backwards time travel. I’d only pointed out where backwards time had been found for real.
At least in my opinion that has been shown as real in real measurements. Then that contrasts with several declarations that Anti-gravity, Wormholes and Exotic matter should be taken seriously with nothing real to back them up.
OK, I see. It's not really fair to accuse me of not following the thread though, your meaning wasn't very clear--it sounded like you were saying you believe wormholes shouldn't be taken seriously because you believed Feynman's idea, as if they were incompatible somehow, rather than just contrasting the amount of supporting evidence for the two ideas.
And remember, there is some possible evidence for negative energy in the form of the casimir effect, even though without a theory of quantum gravity it's not really clear if "energy lower than the ground state of the quantum vacuum" counts as negative energy in the GR sense. As for wormholes, the equations of GR say that if negative energy is possible than stable wormholes should be too, and there's plenty of evidence to support the theory of GR as a whole. Until fairly recently black holes also had no observational evidence to support them, scientists just believed they should be possible based on GR.
RandallB said:
As to realistic as possible fiction writing, I don’t think the philosophical issue arguments will help much.
My point was just that we only have evidence that Feynman's idea works as a mathematical trick, but that it is "philosophical" to treat this as evidence that virtual particles really go back in time (or that virtual particles are real in the first place--see section S3 of http://arnold-neumaier.at/physics-faq.txt for an argument that they should just be thought of as mathematical contrivances). As far as realistic science fiction, this means Feynman's idea can't be used to support the idea of actual time travel--as he said in the letter, it's totally consistent with the causality principle, which says you can't send information backwards in time or faster-than-light.
 
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  • #28
RandallB said:
Are you following along in the thread here?? Negative mass (- energy) was brought up as a means of backwards time travel. I’d only pointed out where backwards time had been found for real.
At least in my opinion that has been shown as real in real measurements. Then that contrasts with several declarations that Anti-gravity, Wormholes and Exotic matter should be taken seriously with nothing real to back them up.
As to realistic as possible fiction writing, I don’t think the philosophical issue arguments will help much.

Wormholes may or may not actually exist, but there are a lot of serious, thoughtful papers about them.

The Morris & Thorne wormholes, in particular, don't require any "new" physics to explain them, just general relativity + the Casimir force. General relativity is the currently accepted theory of gravity, and the Casimir force has been observed in the laboratory.

see for instance

Michael S. Morris and Kip S. Thorne, American Journal of Physics 56, 395 (1988).

Matt Visser has a number of papers on "Lorentzian Wormholes", and even a book.

Frankly, I'm not aware of any papers about RandallB's "backwards in time" idea, which AFAIK stems from some popularized musings by Fenyman that don't appear to me to actually lead to any experimental predictions.

I could be wrong, perhaps RandallB could cite some papers.
 
  • #29
RandallB said:
Then that contrasts with several declarations that Anti-gravity, Wormholes and Exotic matter should be taken seriously with nothing real to back them up. As to realistic as possible fiction writing, I don’t think the philosophical issue arguments will help much.

How many times do we have to bring up the Casimir Effect? This is not a theory or philosophy; it is an actual observed force that is predicted and explained by QM as being... wait for it now... negative energy. Since matter and energy are interchangable, this implies that negative mass is also plausible or even probable. I'm not denying that perhaps someday we will come up with a different explanation for the Casimir Effect, but right now this is the only explanation we have, so it's rather ignorant of you to insist that exotic matter and antigravity have nothing real to back them up. Current theory and physical evidence says that exotic energy exists, period. This implies the existence of exotic matter, and mathematically speaking negative mass should imply negative gravitation.

This is leaps and bounds ahead of Flux Capacitor-esque cheesiness, my friend.

(Btw just to be absolutely clear, though negative energy/mass do have time travel implications, my ideas have nothing to do with backwards time travel. Reverse time dilation=speeding up the passage of time as compared to other frames of reference.)
 
  • #30
pervect said:
The Morris & Thorne wormholes, in particular, don't require any "new" physics to explain them, just general relativity + the Casimir force. General relativity is the currently accepted theory of gravity, and the Casimir force has been observed in the laboratory.
But is it certain that the Casimir force actually qualifies as negative energy in the GR sense? Couldn't it be that a theory of quantum gravity will treat the vacuum ground state as having positive energy, so that even though the energy density between the parallel plates in the Casimir effect is less than that of the vacuum, that doesn't mean it has to be negative?
 
  • #31
LodeRunner said:
... it is an actual observed force that is predicted and explained by QM as being... wait for it now... negative energy.
[...]
...so it's rather ignorant of you to insist that exotic matter and antigravity have nothing real to back them up.
[...]
This is leaps and bounds ahead of Flux Capacitor-esque cheesiness, my friend.
:bugeye: I just want to mention that your candor sounds abrupt, considering that these gentlemen and/or gentlewomen are taking their time to reply to your OP which encourged feedback and discussion. You admit that nothing is proven either way, so perhaps no one is being ignorant?
o:)
 
  • #32
Severian596 said:
:bugeye: I just want to mention that your candor sounds abrupt, considering that these gentlemen and/or gentlewomen are taking their time to reply to your OP which encourged feedback and discussion. You admit that nothing is proven either way, so perhaps no one is being ignorant?
o:)
He was mostly responding to RandallB, and I would consider RandallB's statements more "abrupt" and dismissive of mainstream physics than LodeRunner's.
 
  • #33
Cool. If you're okay with it then I'm probably playing thread police. I'll stop that crap.

Hey LoadRunner, let us know if you publish and what the title is.
:wink:
 
  • #34
Severian596 said:
:bugeye: I just want to mention that your candor sounds abrupt, considering that these gentlemen and/or gentlewomen are taking their time to reply to your OP which encourged feedback and discussion. You admit that nothing is proven either way, so perhaps no one is being ignorant?
o:)

Saying that there is no physical proof for exotic energy/matter is ignorant, because there is proof. Granted, it is not bulletproof proof (heh), and JesseM is quite correct in saying that phenomina arising from QM zero point fuctuations may not translate into negative energy/mass in GR, but there's a big difference between questioning the proof and claiming that it doesn't exist after we've mentioned it it repeatedly.

If I lacked candor and passion I'd make a pretty poor writer. :wink:

I very much appreciate all of the feedback, don't get me wrong, but I don't appreciate someone posting misinformation. If Randall thinks that the Casimir Effect isn't relevant then he should address it directly. If he is wholly unaware of it and is too lazy to research it... :devil:

Severian596 said:
Hey LoadRunner, let us know if you publish and what the title is.

Heh. I don't have a title yet (the working title was The Fall, but I'm not too fond of it), and at the rate I'm going it'll probably be a year or two before I can even think about trying to get it published. Wish I could afford to quit my job and work on it full time...
 
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  • #35
I agree with JesseM: the Casimir Effect proofs the possibility of less energy density than in a vacuum. However, the calculation of the vacuum energy density is not exactly a glorious chapter of modern physics. So I´d say it´s absolutely correct to say that there is no proof for negative energy.
 
  • #36
Ich said:
I agree with JesseM: the Casimir Effect proofs the possibility of less energy density than in a vacuum. However, the calculation of the vacuum energy density is not exactly a glorious chapter of modern physics. So I´d say it´s absolutely correct to say that there is no proof for negative energy.
John Baez has a good discussion of the problems with calculating the vacuum energy density here. He points out that although physicists have failed pretty badly in calculating the vacuum energy from quantum principles, an upper limit can be placed on it from cosmological observations, around 10^-9 joules per cubic meter. So I wonder, can the energy density between plates in the casimir effect go below the vacuum energy density by significantly more than 10^-9 joules per cubic meter? Does anyone know the equation for calculating the energy density between plates in terms of their size and separation? I found a bunch of pages that give an equation for the force (see here, for example), but I'm not sure how to translate this into energy density.
 
  • #37
JesseM said:
John Baez has a good discussion of the problems with calculating the vacuum energy density here.

Thanks for the reference. I am experiencing some sign confusion here, so I did some more reading, specifically

http://arxiv.org/PS_cache/gr-qc/pdf/0001/0001099.pdf

(3) If you believe the recent observational data
regarding the accelerating universe, then the SEC [strong energy condition] is violated on cosmological scales right now!

As nearly as I can figure out, the cosmological constant represents a positive energy density T_00 and (in a locally Minkowskian coordiante system) a negative pressure T_11 = T_22 = T_33 = -T_00.

[Any references otherwise from respectable sources will be gratefully accepted.]

In spite of the positivity of the actual energy density T_00 assigned to the cosmological constant \Lambda, the net effect is one of "effective" anti-gravity. Thus the over-simplification on my part is in thinking/describing that the strong energy condition is one of positive energy density - the energy density due to our positive cosmological constant is technically positive, but it causes the universal expansion to accelerate, not slow down, so it "acts" a lot like negative mass, and it meets the technical defintion of exotic matter in that it violates the strong energy condition.

[add]
Another way of thinking about it - in flat space-time, gravity couples to \rho+3P, so the negative pressure terms do give an effectively "negative" mass in spite of the positve density term
 
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  • #38
Ich said:
I agree with JesseM: the Casimir Effect proofs the possibility of less energy density than in a vacuum. However, the calculation of the vacuum energy density is not exactly a glorious chapter of modern physics. So I´d say it´s absolutely correct to say that there is no proof for negative energy.

Since we apparently live in an "open" universe which will keep on expanding to infinity, doesn't this violate conservation of energy in a rather big way?

Consider a thought experiment; assume there is a way to harness zero-point energy. Again, you would be violating conservation of energy because no matter how much energy you draw off, the Heisenberg Uncertainty Principle forbids us from ever having an energy state of exactly zero.

The Casimir Effect shows us that energy can indeed be harnessed for work (pressing two metal plates together), yet at the same time QM says that we can never use all of the energy (indeed, assuming zero point fluctuations are *just* powerful enough to prevent empty space from violating the Uncertainty Principle, we shouldn't be able to use any of it at all.)

In short, I don't see how we can explain away this creation of energy, unless we also allow the creation of negative energy.
 
  • #39
LodeRunner said:
Since we apparently live in an "open" universe which will keep on expanding to infinity, doesn't this violate conservation of energy in a rather big way?
Ich wasn't talking about conservation of energy, he/she was talking about negative energy, a separate issue. Energy is not conserved globally in general relativity, see here.
LodeRunner said:
The Casimir Effect shows us that energy can indeed be harnessed for work (pressing two metal plates together)
What do you mean by "harnessed", exactly? I don't know how you'd use the two plates to do work, and even if you could, I'd bet that you couldn't get out more energy than you put in...I did some quick googling and found there was a proposal by physicist Robert Forward to extract energy from the vacuum, but this page says:
13. J. Maclay, "Unusual properties of conductive rectangular cavities in the zero point electromagnetic field: Resolving Forward's Casimir energy extraction cycle paradox," PROCEEDINGS of STAIF-99 (Space Technology and Applications International Forum-1999, Albuquerque, NM, January, 1999), edited by M.S. El-Genk, AIP Conference Proceedings 458, American Institute of Physics, New York 1999. Published in hardcopy and CD-ROM by AIP.

This article presents the explanation of why Bob Forwards idea for extracting energy from the vacuum does not work. Usually we think that if the energy density in a box is greater than the energy density outside the box, that there will be an outward force on the walls of the box, which is what Bob’s idea was based on. However, for vacuum energy this it not true!
 
  • #40
Negative energy is related to conservation of energy because mathematically, one should be able to create energy out of nothing if one also creates an equal amount of negative energy.

My point, which you may or may not have refuted (unfortunately I have very little formal education, so many of the details of that link were lost on me), was that assuming all of empty space has a positive energy value would violate conservation of energy, whereas assuming that the value could go negative would not.

JesseM said:
What do you mean by "harnessed", exactly? I don't know how you'd use the two plates to do work, and even if you could, I'd bet that you couldn't get out more energy than you put in...I did some quick googling and found there was a proposal by physicist Robert Forward to extract energy from the vacuum, but this page says:

It's not a matter of extracting useful amounts of power; it's a matter of reducing the amount of zero-point energy in any region of space. If we accept the QM explanation, then it seems as though zero-point energy should be just strong enough to avoid breaking the Uncertainty Principle by allowing us to be too certain about the speed/position/value of a certain point in space.

My point is that if we reduce the amount of vacuum energy by any means, such as using it to push two small metal plates together (converting it into macroscopic kinetic energy), then that energy MUST be replenished somehow in order to prevent over-certainty. My assumption was that this was done by creating negative energy.
Perhaps there is another way it can be replenished, or perhaps the problem is altogether moot if GR and/or QM does allow for creation of energy in some circumstances.

Or perhaps I just don't know what I'm talking about 'cause I'm just a high school dropout wannabe writer who reads up on physics in his spare time...
 
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  • #41
LodeRunner said:
Negative energy is related to conservation of energy because mathematically, one should be able to create energy out of nothing if one also creates an equal amount of negative energy.
But if you're creating an equal amount of negative energy, then you aren't actually violating conservation of energy, right?
LodeRunner said:
My point, which you may or may not have refuted (unfortunately I have very little formal education, so many of the details of that link were lost on me), was that assuming all of empty space has a positive energy value would violate conservation of energy
Why would a positive vacuum energy violate conservation of energy?
LodeRunner said:
It's not a matter of extracting useful amounts of power; it's a matter of reducing the amount of zero-point energy in any region of space.
Who said anything about useful? What I'm saying is that I don't think you can extract any energy from the vacuum using the casimir effect, no matter how tiny. I don't understand what connection you're making between reducing the energy density of a given region of empty space and extracting energy to do work from it.
LodeRunner said:
If we accept the QM explanation, then it seems as though zero-point energy should be just strong enough to avoid breaking the Uncertainty Principle by allowing us to be too certain about the speed/position/value of a certain point in space.
Huh? How would zero-point energy break the uncertainty principle if it were higher? What does it even mean to measure the speed/position of a "point in space", as opposed to a particle?
LodeRunner said:
My point is that if we reduce the amount of vacuum energy by any means, such as using it to push two small metal plates together (converting it into macroscopic kinetic energy), then that energy MUST be replenished somehow in order to prevent over-certainty. My assumption was that this was done by creating negative energy.
I'm not following at all. Are you basing your ideas about how the uncertainty principle relates to zero-point energy on something you've read somewhere, or is this your own idea? If it's something you've read, maybe you could provide a link or a reference so I could better understand your argument.
 
  • #42
I do not know where I first read about the connection of the Casimir Force to the Uncertainty Principle, but a quick wikipedia lookup yields:
In a quantum mechanical system such as the particle in a box or the quantum harmonic oscillator, the lowest possible energy is called the zero-point energy. According to classical physics, the kinetic energy of a particle in a box or the kinetic energy of the harmonic oscillator may be zero if the velocity is zero. Quantum mechanics with its uncertainty principle implies that if the velocity is measured with certainty to be exactly zero, the uncertainty of the position must be infinite. This either violates the condition that the particle remain in the box, or it brings a new potential energy in the case of the harmonic oscillator. To avoid this paradox, quantum mechanics dictates that the minimal velocity is never equal to zero, and hence the minimal energy is never equal to zero.

So it appears as though empty space in QM is subject to the same Uncertainty limitations as particles.

But if you're creating an equal amount of negative energy, then you aren't actually violating conservation of energy, right?

This is exactly my point. Creation of positive and negative energy (or matter) in equal amounts does not violate conservation. Creation of positive-only energy, OTOH, does seem to violate conservation, and your explanation of vacuum energy (that all of empty space has some positive energy but never any negative energy) would seem to fall into this category.

Why would a positive vacuum energy violate conservation of energy?

It wouldn't, provided you could prove that the total vacuum energy in the universe never changed, or that enough negative energy is created to counterbalance the positive.

Who said anything about useful? What I'm saying is that I don't think you can extract any energy from the vacuum using the casimir effect, no matter how tiny. I don't understand what connection you're making between reducing the energy density of a given region of empty space and extracting energy to do work from it.

Well, I thought you said something about always having to "put in" more energy than you'd get out of vacuum energy. My point wasn't getting free energy out of vacuum energy; it was getting ANY energy out of it at all.

If one made microscopic and very light metal plates and put a small amount of pressure on them, not quite enough to move them on its own, but enough to move them after vacuum energy has exterted its influence, then wouldn't that be a case of someone turning vacuum energy into kinetic energy? Wouldn't that mean that we must have LESS vacuum energy than we started with?

My contention is as follows:

The Casimir Effect is a direct consequence of the Uncertainty Principle, and it proves we can convert vacuum energy into another form (kinetic.) BUT, the universe will not allow the reduction of vacuum energy in this manner because this would violate the Uncertainty Principle.

So, if the universe will not allow this reduction, then it must replace the energy lost to maintain Uncertainty. Empty space does not need to have an inherent energy; it just needs to have a non-zero value to preserve Uncertainty. This non-zero value does not need to be positive, so I believe that the most elegant explanation that preserves conservation of energy is to say that zero-point fluctuations include both positive and negative values.

I hope this will clear things up...
 
  • #43
LodeRunner said:
So it appears as though empty space in QM is subject to the same Uncertainty limitations as particles.
I still don't understand, that wikipedia quote was talking about a particle in a box, not empty space. I think the zero-point energy is related to uncertainty in the sense that the quantum fields in quantum field theory are in some sense subject to the uncertainty principle just like particles, but I don't think this has anything to do with measuring the position/speed of a point in space, which I don't think is even a meaningful concept.
LodeRunner said:
This is exactly my point. Creation of positive and negative energy (or matter) in equal amounts does not violate conservation. Creation of positive-only energy, OTOH, does seem to violate conservation, and your explanation of vacuum energy (that all of empty space has some positive energy but never any negative energy) would seem to fall into this category.
But this is just a static amount of energy associated with the vacuum, it isn't the "creation" of positive energy where none was previously.
LodeRunner said:
It wouldn't, provided you could prove that the total vacuum energy in the universe never changed[/url] I think the vacuum energy is thought to have decreased at the end of the inflationary era, but I don't understand the details enough to say whether energy was conserved in this process...if the vacuum energy decreases, perhaps it would be made up for by the creation of a large number of energetic particles, so that the total energy of space + particles remains constant.
LodeRunner said:
Well, I thought you said something about always having to "put in" more energy than you'd get out of vacuum energy. My point wasn't getting free energy out of vacuum energy; it was getting ANY energy out of it at all.
If one made microscopic and very light metal plates and put a small amount of pressure on them, not quite enough to move them on its own, but enough to move them after vacuum energy has exterted its influence then wouldn't that be a case of someone turning vacuum energy into kinetic energy? Wouldn't that mean that we must have LESS vacuum energy than we started with?
I don't know, I don't understand the casimir effect or quantum field theory well enough to address this. You may be right that the increase in kinetic energy of the plates as they are pulled together is balanced by the decreased vacuum energy between them.
LodeRunner said:
The Casimir Effect is a direct consequence of the Uncertainty Principle, and it proves we can convert vacuum energy into another form (kinetic.) BUT, the universe will not allow the reduction of vacuum energy in this manner because this would violate the Uncertainty Principle.
I still don't follow your reasoning. Why would it violate the uncertainty principle? From what I've read, the uncertainty principle's relation to vacuum energy has something to do with the different possible modes of the quantum field carrying energy and momentum. But by placing two plates near each other, you are reducing the number of allowable modes between the plates, because wavelengths that don't divide evenly into the spacing between the plates interfere with themselves. I think each individual mode that's present is still subject to the uncertainty principle in the same way as usual, but some modes are simply no longer present between the plates that are present in empty space, and this has something to do with why the vacuum energy is lower between the plates.
 
  • #44
To avoid this paradox, quantum mechanics dictates that the minimal velocity is never equal to zero, and hence the minimal energy is never equal to zero.

(emphasis mine.)

This means that empty space cannot exist, because empty space=0 energy. This is why we have "quantum foam" or zero-point fluctuations instead. And the Casimir Effect is a direct test of the existence these fluctuations. That is the relationship between the Casimir Effect and Uncertainty--zero-point fluctuations are a consequence of Uncertainty, and the Casimir Effect is a consequence of zero-point fluctuations.

Vacuum energy is present to preserve Uncertainty, and to convert it to another form (in essence taking it away from the vacuum) would allow us to be too certain about the value of a particular point in spacetime.

I can try to find some more links for you, but I'm a little pressed for time. I'm not saying anything that I haven't read in several pop science books (Hawking, etc.) I suppose we could take this to the QM forum and see if we can find a consensus there.

You may be right that the increase in kinetic energy of the plates as they are pulled together is balanced by the decreased vacuum energy between them.

Where else is the kinetic energy coming from, if not a decrease in vacuum energy? Again, this is a Conservation problem. Assuming I'm not horribly wrong about Uncertainty applying to empty space, any vacuum energy converted to another form must be replaced or else we lose that Uncertainty. The idea of negative energy let's us seemlessly replace this lost energy, and no net energy will have been created--thus both Conservation and Uncertainty are preserved.
 
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  • #45
LodeRunner said:
(emphasis mine.)
This means that empty space cannot exist, because empty space=0 energy. This is why we have "quantum foam" or zero-point fluctuations instead. And the Casimir Effect is a direct test of the existence these fluctuations. That is the relationship between the Casimir Effect and Uncertainty--zero-point fluctuations are a consequence of Uncertainty, and the Casimir Effect is a consequence of zero-point fluctuations.

Vacuum energy is present to preserve Uncertainty, and to convert it to another form (in essence taking it away from the vacuum) would allow us to be too certain about the value of a particular point in spacetime.
Ok, but you're not telling me what entity it is that you think is subject to uncertainty here--you said earlier that it was the position/speed of "points in space" which was uncertain, I still think that doesn't make any sense. What I've read in a few places is that different "modes" of the quantum fields which fill empty space carry momentum/energy and are therefore subject to uncertainty, and this is what's responsible for vacuum energy. In between the plates in the Casimir effect, there are fewer possible modes than in free space, therefore the minimum energy is less, without any violation of the uncertainty principle. Are you disagreeing with me about this?
LodeRunner said:
Where else is the kinetic energy coming from, if not a decrease in vacuum energy?
I'd guess you're probably right about this, but again, I don't have enough knowledge of this subject to say for sure. It's conceivable that it would instead be due to a decrease in some form of potential energy, for example.
LodeRunner said:
Assuming I'm not horribly wrong about Uncertainty applying to empty space, any vacuum energy converted to another form must be replaced or else we lose that Uncertainty. The idea of negative energy let's us seemlessly replace this lost energy, and no net energy will have been created--thus both Conservation and Uncertainty are preserved.
Just to be clear, do you think this is the opinion of mainstream physicists, or are you expressing your own ideas here? Like I said before, I don't think mainstream physicists would say there is any problem with the uncertainty principle being violated in the Casimir effect, in fact I think the lower energy density between the plates can be calculated from the uncertainty principle in exactly the same way that the energy of the ordinary vacuum is calculated from it (by looking at the minimum energy of all the allowable modes in each case, with more modes being allowed in empty space than between the plates).
 
  • #46
I don't want anyone to get the impression that I'm pulling stuff out of my ass, so:

Mainstream physicists have said that the Casimir Effect arises as a consequence of Uncertainty, not that it violates it. Mainstream physicists have also brought up the possibility of negative energy or negative mass, and I have heard them use the Casimir Effect as one such example.

I have made the (possibly wrong) leap of logic to connect these two ideas and show why negative energy may be necessary in order to preserve Conservation while simultaneously preserving Uncertainty. I have not heard this idea from any source; it is just the result of me trying to make several different mainstream ideas fit together.

My claim that a reduction in energy would result in Uncertainty breaking is my own. Since I have always heard the Casimir Effect explained in terms of the Uncertainty Principle, I assume that the fluctuations are just strong enough to preserve Uncertainty. It may be that there is a margin there, and that it is possible to convert some vacuum energy into other forms but not enough to break Uncertainty, but because of the way it was explained to me, I have no reason to believe that such an excess of vacuum energy exists.

My claim that an increase in vacuum energy (e.g. to replace that loss through the Casimir Effect) violates Conservation is also my own, though I think it is a fairly straightforward assumption.

Ok, but you're not telling me what entity it is that you think is subject to uncertainty here--you said earlier that it was the position/speed of "points in space" which was uncertain, I still think that doesn't make any sense. What I've read in a few places is that different "modes" of the quantum fields which fill empty space carry momentum/energy and are therefore subject to uncertainty, and this is what's responsible for vacuum energy. In between the plates in the Casimir effect, there are fewer possible modes than in free space, therefore the minimum energy is less, without any violation of the uncertainty principle. Are you disagreeing with me about this?

Interesting. I have never heard this explanation before. I have always read that it is the appearence and disappearence of virtual particles, the kind that are responsible for Hawking Radiation (one particle of the particle/antiparticle virtual pair appears just barely within the event horizon of a black hole and the other one appears just barely outside of it. The one outside escapes to freedom and becomes "real" whereas the other one falls into the black hole and reduces its mass through QM weirdness that I do not fully understand.) It was my understanding that all of empty space was composed of these virtual particle pairs, constantly appearing and annihilating one another--the quantum "foam". They have no mass and usually have no effect, except that Uncertainty commands that they MUST have a mass or energy value, at least sometimes.

And if all of my assumptions are correct, then they must also have an negative mass (or negative energy), at least sometimes.

Anyway, I really must be getting to bed now. It's been great debating with you... will come back again and check tonight or Friday night.
 
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  • #47
What are uncertain in quantum mechanics are complementary pairs of observables. There are several of these; the easiest to prove from Schroedinger's (or any other quantum) equation is momentum and position. The more accurately you know momentum the more uncertain you must be about position, and vice versa. If you multiply the uncertainties together you get Planck's constant, so if you were to plot the uncertainty on axes of position for x and momentum for y, the uncertainty curve would be a hyperbola with those two axes as asymptotes.

Another set of complementary observables is spin around different axes. If you measure the spin around the z-axis, thus reducung its uncertainty to zero, the spins around the x and y-axes become completely uncertain. This is the physics behind the repeated Stern-Gerlach experiments described by Feynmann.

The case of energy and time is a little different. It turns on they behave just like complementary observables, but because energy is an observable but time is not, the proof is different.

I don't see any need for negative energy to balance conservation of energy in quantum mechanics. energy is conserved up to observation in quantum mechanics. And just as there is no preferred frame in relativity from which you can see "what really happens", so there is no opportunity in quantum mechanics to see the unobservable. For more on this, check out the threads on the quantum forum about hidden variables and Bell's theorem.
 
  • #48
pervect said:
some popularized musings by Fenyman - don't appear to me to actually lead to any experimental predictions.
I could be wrong, perhaps RandallB could cite some papers.
I wasn’t referring to his musings; Fenyman’s Diagrams have lead to improvements, discoveries, and understands in working out and planning partial collisions.
Work through some of the mildly complicated ones, you don’t need a cited papers to find them. Once you understand them & where they are useful, the hard part is to imagine a way to workout the issues without backwards time. Maybe with a MWI/HUP concept but I’d find that hard to implement usefully as the diagrams already have been.

As to the Casimir force—“ it is an actual observed force that is predicted and explained by QM as negative energy.” As it’s only explanation!
Therefore by using that explanation:
“we KNOW exotic energy & matter exists, period”.
Therefore by implication we know:
Negative gravitation even Wormholes must be real!
This is great! with ‘proof’ like this we should be able to show that HUP and thus QM is just as exclusively correct as that theory claims to be!
– except that was the assumption that started all these 'proofs'!

The point is; mind numbing "circular logic" like this may have some use in science (I’m not sure where), but why use something that hard to follow in fiction, when you already know that the cheesy ‘Flux Capacitor’ style is proven as acceptable anyway.

Now if this thread has turned to finding what’s ‘correct’, I don’t think Casimir will do. Entanglement is the only recognized non-circular ‘proof’ for QM/HUP and we already have two or three active threads debating that issue.

Accepting backwards time as something real that needs to be figured out is just one thing.
QM – Casimir – wormhole – HUP is a spaghetti bowl. I’ll take Occam as my guide.

SO, for me my money’s on backwards time a la Fenyman’s Diagrams is shown to be real and not a trick before Negative Gravitation is. In fact I’d bet that a Theory proving so would also show QM/HUP to wormholes as wrong.
Since I seem to be in a minority on that at least I should get good odds, do ya’ suppose they have a line in Vegas?
RB
 
  • #49
RandallB said:
Now if this thread has turned to finding what’s ‘correct’, I don’t think Casimir will do. Entanglement is the only recognized non-circular ‘proof’ for QM/HUP and we already have two or three active threads debating that issue.
You are doubting QM/HUP?? These fall into the realm of very well-established physics. This board has a rule against trying to call into question established physics, so I wonder which active threads you're talking about.
RandallB said:
SO, for me my money’s on backwards time a la Fenyman’s Diagrams is shown to be real and not a trick before Negative Gravitation is. In fact I’d bet that a Theory proving so would also show QM/HUP to wormholes as wrong.
What does "shown to be real" mean here? What possible test could distinguish backwards-time-as-something-real from backwards-time-as-a-useful-mathematical-trick, since it's clear that quantum field theory does respect causality and thus cannot be used to actually send messages backwards in time? I still think you're confusing physics with philosophy--unless a particular idea leads to testable consequences, it ain't physics.
 
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  • #50
LodeRunner said:
I don't want anyone to get the impression that I'm pulling stuff out of my ass, so:

Mainstream physicists have said that the Casimir Effect arises as a consequence of Uncertainty, not that it violates it. Mainstream physicists have also brought up the possibility of negative energy or negative mass, and I have heard them use the Casimir Effect as one such example.
Agreed (although by 'negative energy' I think they just mean something like 'energy lower than that of the vacuum')
LodeRunner said:
My claim that a reduction in energy would result in Uncertainty breaking is my own. Since I have always heard the Casimir Effect explained in terms of the Uncertainty Principle, I assume that the fluctuations are just strong enough to preserve Uncertainty. It may be that there is a margin there, and that it is possible to convert some vacuum energy into other forms but not enough to break Uncertainty, but because of the way it was explained to me, I have no reason to believe that such an excess of vacuum energy exists.
I don't understand what you mean by "the fluctuations are just strong enough to preserve uncertainty", or why converting vacuum energy into other forms (like the kinetic energy of the plates) would "break" uncertainty.
LodeRunner said:
My claim that an increase in vacuum energy (e.g. to replace that loss through the Casimir Effect) violates Conservation is also my own, though I think it is a fairly straightforward assumption.
I don't understand this either. In the Casimir effect, the vacuum energy between the plates decreases, it doesn't increase. Are you saying the vacuum energy would increase in some other region to compensate? I'm pretty sure that is not the case...like you suggested earlier, energy conservation may just have to do with the fact that the kinetic energy of the plates balances the decrease in vacuum energy in the space between them, or it may have something to do with creation/destruction of energetic particles, I'm not sure.
LodeRunner said:
Interesting. I have never heard this explanation before. I have always read that it is the appearence and disappearence of virtual particles, the kind that are responsible for Hawking Radiation (one particle of the particle/antiparticle virtual pair appears just barely within the event horizon of a black hole and the other one appears just barely outside of it. The one outside escapes to freedom and becomes "real" whereas the other one falls into the black hole and reduces its mass through QM weirdness that I do not fully understand.) It was my understanding that all of empty space was composed of these virtual particle pairs, constantly appearing and annihilating one another--the quantum "foam". They have no mass and usually have no effect, except that Uncertainty commands that they MUST have a mass or energy value, at least sometimes.
Sure, in quantum field theory I think it's true that to understand the properties of empty space you have to do a sum of Feynman diagrams in which virtual particles appear out of nothing and then annihilate each other. But what's your understanding of how this would explain the Casimir effect? Presumably the virtual particles would have to be behaving differently between the plates than they do in empty space, but why? Reading a little more, I think the usual explanation in terms of virtual particles is probably equivalent to what I was saying about the different "modes" of the quantum field--virtual particles have wavelengths just like modes, and in both cases only wavelengths that divide evenly into the separation between plates can avoid cancelling themselves out, so only these wavelengths contribute to the properties of the vacuum between the plates. See [URL='https://www.physicsforums.com/insights/author/john-baez/']John Baez's page on the Casimir effect[/url], for example:
The Casimir effect is a small attractive force which acts between two close parallel uncharged conducting plates. It is due to quantum vacuum fluctuations of the electromagnetic field.

The effect was predicted by the Dutch physicist Hendrick Casimir in 1948. According to the quantum theory, the vacuum contains virtual particles which are in a continuous state of fluctuation (see physics FAQ article on virtual particles). Casimir realized that between two plates, only those virtual photons whose wavelengths fit a whole number of times into the gap should be counted when calculating the vacuum energy. The energy density decreases as the plates are moved closer which implies there is a small force drawing them together.
And here's an article from "Physics World" which gives a longer explanation:
Understanding the Casimir force

Although the Casimir force seems completely counterintuitive, it is actually well understood. In the old days of classical mechanics the idea of a vacuum was simple. The vacuum was what remained if you emptied a container of all its particles and lowered the temperature down to absolute zero. The arrival of quantum mechanics, however, completely changed our notion of a vacuum. All fields - in particular electromagnetic fields - have fluctuations. In other words at any given moment their actual value varies around a constant, mean value. Even a perfect vacuum at absolute zero has fluctuating fields known as "vacuum fluctuations", the mean energy of which corresponds to half the energy of a photon.

However, vacuum fluctuations are not some abstraction of a physicist's mind. They have observable consequences that can be directly visualized in experiments on a microscopic scale. For example, an atom in an excited state will not remain there infinitely long, but will return to its ground state by spontaneously emitting a photon. This phenomenon is a consequence of vacuum fluctuations. Imagine trying to hold a pencil upright on the end of your finger. It will stay there if your hand is perfectly stable and nothing perturbs the equilibrium. But the slightest perturbation will make the pencil fall into a more stable equilibrium position. Similarly, vacuum fluctuations cause an excited atom to fall into its ground state.

The Casimir force is the most famous mechanical effect of vacuum fluctuations. Consider the gap between two plane mirrors as a cavity (figure 1). All electromagnetic fields have a characteristic "spectrum" containing many different frequencies. In a free vacuum all of the frequencies are of equal importance. But inside a cavity, where the field is reflected back and forth between the mirrors, the situation is different. The field is amplified if integer multiples of half a wavelength can fit exactly inside the cavity. This wavelength corresponds to a "cavity resonance". At other wavelengths, in contrast, the field is suppressed. Vacuum fluctuations are suppressed or enhanced depending on whether their frequency corresponds to a cavity resonance or not.

An important physical quantity when discussing the Casimir force is the "field radiation pressure". Every field - even the vacuum field - carries energy. As all electromagnetic fields can propagate in space they also exert pressure on surfaces, just as a flowing river pushes on a floodgate. This radiation pressure increases with the energy - and hence the frequency - of the electromagnetic field. At a cavity-resonance frequency the radiation pressure inside the cavity is stronger than outside and the mirrors are therefore pushed apart. Out of resonance, in contrast, the radiation pressure inside the cavity is smaller than outside and the mirrors are drawn towards each other.

It turns out that, on balance, the attractive components have a slightly stronger impact than the repulsive ones. For two perfect, plane, parallel mirrors the Casimir force is therefore attractive and the mirrors are pulled together. The force, F, is proportional to the cross-sectional area, A, of the mirrors and increases 16-fold every time the distance, d, between the mirrors is halved: F ~ A/d^4. Apart from these geometrical quantities the force depends only on fundamental values - Planck's constant and the speed of light.
Finally, this site talks about the connection to the uncertainty principle:
The basis of zero-point energy is the Heisenberg uncertainty principle, one of the fundamental laws of quantum physics. According to this principle, the more precisely one measures the position of a moving particle, such as an electron, the less exact the best possible measurement of momentum (mass times velocity) will be, and vice versa. The least possible uncertainty of position times momentum is specified by Planck's constant, h. A parallel uncertainty exists between measurements involving time and energy. This minimum uncertainty is not due to any correctable flaws in measurement, but rather reflects an intrinsic quantum fuzziness in the very nature of energy and matter.

A useful calculational tool in physics is the ideal harmonic oscillator: a hypothetical mass on a perfect spring moving back and forth. The Heisenberg uncertainty principle dictates that such an ideal harmonic oscillator -- one small enough to be subject to quantum laws -- can never come entirely to rest, since that would be a state of exactly zero energy, which is forbidden. In this case the average minimum energy is one-half h times the frequency, hf/2.

Radio waves, light, X-rays, and gamma rays are all forms of electromagnetic radiation. Classically, electromagnetic radiation can be pictured as waves flowing through space at the speed of light. The waves are not waves of anything substantive, but are in fact ripples in a state of a field. These waves do carry energy, and each wave has a specific direction, frequency and polarization state. This is called a "propagating mode of the electromagnetic field."

Each mode is subject to the Heisenberg uncertainty principle. To understand the meaning of this, the theory of electromagnetic radiation is quantized by treating each mode as an equivalent harmonic oscillator. From this analogy, every mode of the field must have hf/2 as its average minimum energy. That is a tiny amount of energy, but the number of modes is enormous, and indeed increases as the square of the frequency. The product of the tiny energy per mode times the huge spatial density of modes yields a very high theoretical energy density per cubic centimeter.

From this line of reasoning, quantum physics predicts that all of space must be filled with electromagnetic zero-point fluctuations (also called the zero-point field) creating a universal sea of zero-point energy.
So again, I think that somehow the uncertainty principle can be used to find each individual wavelength's contribution to the vacuum energy, and the explanation for the lower energy between the plates is just that fewer wavelengths are allowed. I may be misunderstanding since I'm certainly no expert on quantum field theory, but that's the impression I get from articles like these.
 
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