Is reverse time dilation posssible?

[pervect]

What’s that got to do with it!
– obviously the bomb can be moved as I defined it to demonstrate the SR can produce “Fast Time”, making up an extra requirement doesn’t help demonstrate how SR works.
With no bogus extra requirement to insist that the entire Earth be accelerated– as you point out: Of course it has merit, Except I don’t see any “certain amount” of limitation to it – SR simply enough when applied correctly can produce “fast time” effects requested, in fact you cannot do the ‘the twins’ without producing it from somebody’s view.

SR cannot speed up somone significantly with respect to the bulk of humanity, unless the bulk of humanity can somehow be accelerated to relativistic velocities.

Speeding up the bulk of humanity is highly impractical, among other problems, such as the political issues of gaining its consent to the process.

The preferred frame of reference here is created not by physics, but by the choice of most people of where to live.

Note that a _very_ small speedup can be obtained by the fact that the bulk of humanity lives at the bottom of a gravity well. This is a GR effect, and is extremely tiny - it would not be useful for the stated plot purposes. Any large speedup with respect to the bulk of humanity is going to require some other mechanism (like the exotic matter hollow sphere).

 

[JesseM]

No problem I think we both agree that the fast time affect can be accomplished be speed SR or correct portioning in greatly different gravitational fields (GR) close enough that moving between those positions would be useful.

We just disagree on the implications of exotic matter, negative matter. To me they imply “backwards time”.

If you're saying you could go backwards in time just by getting near some exotic matter, then I'm pretty sure you're wrong. Remember, any time physicists talk about traveling backwards in time they're doing it in the context of what's allowed under general relativity, and although it's true that exotic matter plays an integral role in certain spacetimes where time travel is possible like ones involving wormholes, that doesn't mean that GR predicts that just having a clump of exotic matter somewhere would allow you to travel back in time.

It’s just one reason but not the only reason one that I don’t believe the exotic / negative matter idea is valid or useful, even theoretically. And that no “wormhole” of any size or type will ever be found to validate the concept.

Do you believe in features of black holes that GR predicts but that there is zero experimental evidence for, like the idea that they have "event horizons" beyond which even light cannot escape? If so, why do you think one unobserved prediction of GR is more likely than another?

So for me the idea that exotic matter, negative matter means “backwards time” is fine because none of them are any more real than a “flux capacitor”

As hellfire said in answer to a question of mine earlier, the amount by which the vacuum energy between plates in the casimir effect can be less than the regular vacuum energy is significantly more than cosmological evidence suggests the regular vacuum energy could be above zero, which is good reason to believe that negative energy in the GR sense is possible.

 

[daytripper]

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.

I'm no expert and I haven't read this entire thread so excuse me if I'm repeating an answer or making an ass of myself, but it seems that if you had negative-mass that repelled objects, rather than attract them, you would have space warping out instead of warping in, pushing instead of pulling. You're still constantly accelerating due to the warp in spacetime, reguardless of the direction. I'd say the gravitational time dilation would be the same in this repulsive field as in a planet's attractive field. Maybe I'm in over my head on this one but it seems correct, if this is wrong, could someone explain to me why?

 

[JesseM]

I'm no expert and I haven't read this entire thread so excuse me if I'm repeating an answer or making an ass of myself, but it seems that if you had negative-mass that repelled objects, rather than attract them, you would have space warping out instead of warping in, pushing instead of pulling.

I don't know if "warping out" as opposed to "warping in" is really meaningful here--see my post #21 to nemosum:

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.

You're still constantly accelerating due to the warp in spacetime, reguardless of the direction. I'd say the gravitational time dilation would be the same in this repulsive field as in a planet's attractive field. Maybe I'm in over my head on this one but it seems correct, if this is wrong, could someone explain to me why?

Presumably you have to solve the Einstein field equations using the assumption of a negative energy density to solve this rigorously. I'm not too knowledgeable about GR, but pervect is, and he's said on this thread that negative mass/energy would indeed cause this sort of "reverse time dilation" (ie time running faster instead of slower for observers near the negative mass). I don't know if there's any nontechnical way of understanding why this is true--pervect, any thoughts?

 

[daytripper]

I don't know if "warping out" as opposed to "warping in" is really meaningful here--see my post #21 to nemosum: Presumably you have to solve the Einstein field equations using the assumption of a negative energy density to solve this rigorously. I'm not too knowledgeable about GR, but pervect is, and he's said on this thread that negative mass/energy would indeed cause this sort of "reverse time dilation" (ie time running faster instead of slower for observers near the negative mass). I don't know if there's any nontechnical way of understanding why this is true--pervect, any thoughts?

I suppose if pervect says so, it would be so. I don't understand why it would, but I'm in no position to disagree. haha. i just figured that "reverse time dialation" would require negative velocity and since velocity isn't vectored, it can't be negative... as far as taking the rubber sheet metaphor too far, I've never much cared for that metaphor, I've allways preferred to think of a 3d matrix with warped cells getting "smaller" as you get closer to the center of mass. that's what a spacetime warp would look like if we could see it in 3 dimensions, right?

 

[JesseM]

I suppose if pervect says so, it would be so. I don't understand why it would, but I'm in no position to disagree. haha. i just figured that "reverse time dialation" would require negative velocity and since velocity isn't vectored, it can't be negative...

Why negative velocity? Velocity-based time dilation in SR is different from gravitational time dilation in GR.

as far as taking the rubber sheet metaphor too far, I've never much cared for that metaphor, I've allways preferred to think of a 3d matrix with warped cells getting "smaller" as you get closer to the center of mass. that's what a spacetime warp would look like if we could see it in 3 dimensions, right?

Wouldn't this only be a way of thinking of the warping of space, not the warping of spacetime?

 

[daytripper]

Why negative velocity? Velocity-based time dilation in SR is different from gravitational time dilation in GR. Wouldn't this only be a way of thinking of the warping of space, not the warping of spacetime?

I'm sorry, I seem to have a lack of understanding. I thought that spacetime would warp along with space. Meaning... as space warped, so did spacetime, explaining gravitational time dialation. And again, please excuse my ignorance, i thought velocity-based time dilation and gravitational time dilation were just two names for the same thing (with different causes). I'll read up on the difference more.

 

[RandallB]

If you're saying you could go backwards in time just by getting near some exotic matter, then I'm pretty sure you're wrong. Remember, any time physicists talk about traveling backwards

casimir effect ... suggests ... could be...reason to believe ...sense is possible.

Can’t beat qualifiers like that maybe it could be write.

Yes - exotic leads to backwards. (but I don't but exotic)
Before saying nobody is saying backwards time is real or what is meant “any time physicists talk” it; find some reading on:
Kip Thorne – Caltech, black holes and gravitational physics, co-founder LIGO Project
Look for his comments and “discussions” and consensus compromise view with Hawking on the issue of BACKWARDS TIME Travel as a result of exotic/negative - - - ; I’m sure you can find a section on those debates with Kip in one of the Hawking books. As a Sci Adviser you need to catch up on some reading.

For the GR case:

Speeding up the bulk of humanity is highly impractical, among other problems, such as the political issues of gaining its consent to the process.

Our reluctant hero of space; We already did speed up “the bulk of humanity” by having your twin sister fly off with the second bomb.

As to using GR to speed up “the bulk of humanity” no problem. It’s in episode 2 your sister found out that she had the just the second bomb – the first is in Ming’s secret hidden lab in a deep gravity well where he’s been all these years! There only 5 days pass for every 5 months for “the bulk of humanity” on relative fast time!. Save us again pervect save us…. And please don’t tell me Pervect, JesseM, & LodeRunner combined don’t have the Sci-fi creativity to sort out the details of hiding a deep gravity well, or getting rid of Ming. If you have to just use a worm hole or flux capacitor and be done with it just do a better job on the plot line.

 

[JesseM]

Can’t beat qualifiers like that maybe it could be write.
Yes - exotic leads to backwards. (but I don't but exotic)

Not automatically, no.

Before saying nobody is saying backwards time is real or what is meant “any time physicists talk” it; find some reading on:
Kip Thorne – Caltech, black holes and gravitational physics, co-founder LIGO Project
Look for his comments and “discussions” and consensus compromise view with Hawking on the issue of BACKWARDS TIME Travel as a result of exotic/negative - - - ; I’m sure you can find a section on those debates with Kip in one of the Hawking books. As a Sci Adviser you need to catch up on some reading.

It's you who needs to do more reading here. I've read a number of books by Kip Thorne, and nowhere have I seen him say exotic matter automatically leads to time travel. Exotic matter + wormholes (or other weird spacetimes, perhaps) do lead to time travel in plain ol' classical GR, but I don't think there's there's any way to create a wormhole from scratch in classical GR (because you can't change the topology of spacetime), and in any case people who advocate "chronology protection" like Hawking do not say that it's because they think exotic matter can't exist, the usual argument is that quantum effects (vacuum fluctuations) would destroy a wormhole at the exact moment that one mouth enters the light cone of the other one, which is when time travel would become possible. See my post #10 on this thread for more background on this idea. Note that this idea would allow for the existence of stable wormholes held open by exotic matter if there is a spacelike separation between the mouths, in which case there is no danger of time travel. Kip Thorne's Black Holes and Time Warps has a more detailed discussion of vacuum fluctuations preventing time travel by destroying wormholes on pp. 517-521, and on p. 520 he discusses Hawking's own spin on this argument. Hawking also has an essay on chronology protection in the book The Future of Spacetime, where he mentions some other (probably related) arguments involving quantum effects that would make time travel impossible, like the idea that such effects will cause the energy density to go to infinity on the "Cauchy horizon", the boundary of the region of spacetime where time travel would become possible. He also mentions an additional argument in favor of negative energy densities, different from the Casimir effect:

The evaporation of black holes shows that the quantum energy-momentum tensor of matter can sometimes warp spacetime in the direction that would be needed to build a time machine. One might imagine therefore that some very advanced civilization could arrange for the expectation value of the energy density to be sufficiently negative to form a time machine that could be used for macroscopic objects.

He then goes on to describe how the energy density would go to infinity on the Cauchy horizon, so that "In practice this would mean that a person or space probe that tried to cross the Cauchy horizon to get into the time machine would get wiped out by a bolt of radiaton!" Anyway, the point here is that Hawking seems to be saying that the theory of black hole evaporation demands the existence of negative energy, and that his argument for "chronology protection" once again are based effects from semi-classical quantum gravity, not on denying the idea that negative energy is allowed by the laws of physics.

Our reluctant hero of space; We already did speed up “the bulk of humanity” by having your twin sister fly off with the second bomb.

Again, suppose the bomb cannot be accelerated without blowing up, and it's currently in Earth orbit experiencing 0 G. Then you have no way to move the bomb out of its orbit, so "reverse time dilation" is your only hope. Pervect also suggested another scenario where an alien invasion fleet is approaching the earth, and they will arrive before you have time to develop adequate defensive technology--how would you buy more time in this case, without reverse time dilation?

 

[RandallB]

It's you who needs to do more reading here. I've read a number of books by Kip Thorne, and nowhere have I seen him say exotic matter automatically leads to time travel.

? I’ve seen him speak and he delights in talking about Backwards Time travel.
Try Hawking - Nutshell – Chapter Five
(Not that agree with Kip or Steve)

As to fast time: I’ve set the scenes in two examples to write from that uses SR or GR – done.
If you want to set the scene in what ever improbable way and expect me to work from there, that’s not how writing works – but if I must; I’ll use a flux-capacitor – done again.
We’re talking Sci-Fi here for crying out loud.

This thread is way over done – good luck in the writing.
Later.

 

[JesseM]

? I’ve seen him speak and he delights in talking about Backwards Time travel.

I didn't say he didn't talk about backwards time travel, I said "nowhere have I seen him say exotic matter automatically leads to time travel." Did you read the section of Black Holes and Time Warps that I mentioned? In that section he discusses a way in which you could have both wormholes (held open by exotic matter) and "chronology protection", as I already discussed in my last post.

Try Hawking - Nutshell – Chapter Five

Does he say that exotic matter automatically leads to time travel here? If so, he would be contradicting what he wrote in The Future of Spacetime, so I seriously doubt it. Please go back and check, and if you really think that's what he's saying, you're probably just misunderstanding him--perhaps you could post a quote or a page number so I could see what you're interpreting to mean this.

As to fast time: I’ve set the scenes in two examples to write from that uses SR or GR – done.
If you want to set the scene in what ever improbable way and expect me to work from there, that’s not how writing works – but if I must; I’ll use a flux-capacitor – done again.

Look, if you don't personally believe in exotic matter that's fine, but it's absurd to suggest that exotic matter is in league with "flux capacitors" in terms of scientific plausibility. Exotic matter is no more of a far-out possibility than black hole evaporation, for example (Hawking suggested in the quote I posted that black hole evaporation actually demands the possibility of negative energy densities).

 

[LodeRunner]

60 hour work weeks suck.

This thread is way over done – good luck in the writing.
Later.

I disagree. It's an interesting subject to discuss and debate.

But yes, my original purpose is satisfied. Despite your not-entirely-coherent objections (no offense intended), the consensus seems to be that IF exotic matter exists, it should induce negative time dilation. I'm willing to assume the existence of exotic matter for purposes of my story; I was not willing to assume that exotic matter exists AND that it would exhibit this particular property.

And JesseM is right; exotic matter does not automatically bring about backwards time travel. It is a COMPONENT of backwards time travel theories (such as "propping open" a wormhole), but simply being near a quantity of exotic matter would not cause one to travel back in time. This doesn't make any rational or intuitive sense on several levels, and I'm pretty sure no mainstream physicist has claimed such a thing.


Re: JesseM

I'm beginning to think I'm out of my league here. While I have studied the math and details behind SR and GR, I have only a passing understanding of Uncertainty. It may be that I'm spouting complete nonsense.

Like I said before, the very first time I heard virtual particles explained, it was in terms of the Uncertainty principle. "Zero is too certain", the book said... or something to that effect. It said that empty space could not ever have an absolutely certain value of zero, because that would violate Uncertainty. Thus I visualize vacuum energy/virtual particles as being this energy that fills empty space to prevent it from being, well, truly empty. And I envision it being JUST strong enough to satisfy the mathematical requirements of Uncertainty (again, I know vaguely of Plank's constant and such, but I do not know the formulas.) Thus, if someone takes away ANY of that energy (kinetic energy of the Casimir plates), it must be replaced or else Uncertainty is violated. Negative energy is just a way of replacing that energy without violating conversation of energy.

But you seem to disagree with me on the "Uncertainty of empty points in space" concept, and I simply lack the knowledge to have a debate on this point (nor do I have the time to spare to do serious research ATM.) All I can repeat is that this is how I understood virtual particles and the Casimir Effect to work. If that book I read used a very badly worded analogy or simplification, then my premise is wrong.

Thanks for the replies guys; it's been fun. I'm all for continuing the discussion (especially regarding whether the Casimir Effect is an example or implies the existence of negative energy), but if no one other than RandallB objects to pervect's analysis, I think my original question has been answered.

 

[JamesAU007]

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?

Now although not possible yet, what about the possibility that once matter or particles exceed lightspeed time actually begins to reverse.
If the faster you go towards lightspeed the slower your relative time goes then once you pass lightspeed wouldn't time begin to reverse. As for anything traveling at lightspeed time appears to stop.
It's reverse thinking in the fact that the slower you go the faster your time goes ( relative )

Just a different take on an old problem :)

Reverse time dilation must occurr naturally if postive time dilation does now. Everything in the universe has it's opposite.

This a very crude scribble i drew up to explain what i am talking about - it is very approx in numbers and very crude as you can see, i only want to show on paper what i am trying to explain.

 

[JesseM]

If the faster you go towards lightspeed the slower your relative time goes then once you pass lightspeed wouldn't time begin to reverse.

No, if you try to calculate time dilation for a clock moving FTL using the Lorentz transformation, you actually find that the formula predicts its rate of ticking would be imaginary, which seems to be a meaningless result. However, it is true that if you could send signals faster than light, then according to relativity you could also send information backwards in time; however, this has nothing to do with how time passes for the FTL particle itself, it's just a consequence of how different slower-than-light observers disagree on the order of events (specifically, if a signal moves FTL in some reference frame, there will be other slower-than-light frames where the signal was actually received at an earlier time than it was sent). See this thread for a discussion.

Incidentally, take a look at the IMPORTANT! Read before posting thread--this is not a forum for speculations about new physics ideas that have no justification in terms of existing mainstream physics or experimental results.

 

[JamesAU007]

Ok thank you for the explanation.

I will read the thread you provided.

 

[JamesAU007]

Wow I haven't been online (this site) for a long time although after a recent discussion and then searching reverse time dilation online it seems as though this topic has gained some interest!?

As I said to begin with I know the diagram I posted was very crude and rough, there is no complex math behind it...

It was a simple graph and the way I could visualize reverse/negative time dilation...

It's just interesting to see that since I first posted this topic that there has been a minor increase in interest :)

As i said to begin with, if Time Dilation exists (positive) then there must also be an opposite or negative...