Want time travel? Keep dreaming.

[GrandMasterTerwynn]

Because you're not going to get it . . . not with wormholes, anyway.

Wormholes contort the fabric of the Universe
For budding time travellers, the future (or should that be the past?) is starting to look bleak.

Hypothetical tunnels called wormholes once looked like the best bet for constructing a real time machine.

These cosmic shortcuts, which link one point in the Universe to another, are favoured by science fiction writers as a means both of explaining time travel and of circumventing the limitations imposed by the speed of light.

The concept of wormholes will be familiar to anyone who has watched the TV programmes Farscape, Stargate SG1 and Star Trek: Deep Space Nine.

The opening sequence of the BBC's new Doctor Who series shows the Tardis hurtling through a "vortex" that suspiciously resembles a wormhole - although the Doctor's preferred method of travel is not explained in detail.

But the idea of building these so-called traversable wormholes is looking increasingly shaky, according to two new scientific analyses.

Remote connection

A common analogy used to visualise these phenomena involves marking two holes at opposite ends of a sheet of paper, to represent distant points in the Universe. One can then bend the paper over so that the two remote points are positioned on top of each other.


[The wormholes] you would like to build - the predictable ones where you can say Mr Spock will land in New York at 2pm on this day - those look like they will fall apart
Stephen Hsu, University of Oregon
If it were possible to contort space-time in this way, a person might step through a wormhole and emerge at a remote time or distant location.

The person would pass through a region of the wormhole called the throat, which flares out on either side.

According to one idea, a wormhole could be kept open by filling its throat, or the region around it, with an ingredient called exotic matter.

This is strange stuff indeed, and explaining it requires scientists to look beyond the laws of classical physics to the world of quantum mechanics.

Exotic matter is repelled, rather than attracted, by gravity and is said to have negative energy - meaning it has even less than empty space.

Law breaker

But according to a new study by Stephen Hsu and Roman Buniy, of the University of Oregon, US, this method of building a traversable wormhole may be fatally flawed. In a paper published on the arXiv pre-print server, the authors looked at a kind of wormhole in which the space-time "tube" shows only weak deviations from the laws of classical physics.

These "semi-classical" wormholes are the most desirable type for time travel because they potentially allow travellers to predict where and when they would emerge.

The concept is a favourite of science fiction writers
Wormholes entirely governed by the laws of quantum mechanics, on the other hand, would likely transport their payloads to an undesired time and place.

Calculations by the Oregon researchers show a wormhole that combines exotic matter with semi-classical space-time would be fundamentally unstable.

This result relies in part on a previous paper in which Hsu and Buniy argued that systems which violate a physical principle known as the null energy condition become unstable.

"We aren't saying you can't build a wormhole. But the ones you would like to build - the predictable ones where you can say Mr Spock will land in New York at 2pm on this day - those look like they will fall apart," Dr Hsu said.

Tight squeeze

A separate study by Chris Fewster, of the University of York, UK, and Thomas Roman, of Central Connecticut State University, US, takes a different approach to tackling the question of wormholes.

Amongst other things, their analysis deals with the proposal that wormhole throats could be kept open using arbitrarily small amounts of exotic matter.

Fewster and Roman calculated that, even if it were possible to build such a wormhole, its throat would probably be too small for time travel.

It might - in theory - be possible to carefully fine-tune the geometry of the wormhole so that the wormhole throat became big enough for a person to fit through, says Fewster.

But building a wormhole with a throat radius big enough to just fit a proton would require fine-tuning to within one part in 10 to the power of 30. A human-sized wormhole would require fine-tuning to within one part in 10 to the power of 60.

"Frankly no engineer is going to be able to do that," said the York researcher.

The authors are currently preparing a manuscript for publication.

Supporting view

However, there is still support for the idea of traversable wormholes in the scientific community. One physicist told BBC News there could be problems with Hsu's and Buniy's conclusions.

"Violations of the null energy condition are known to occur in a number of situations. And their argument would prohibit any violation of it," the scientist commented.

"If that's true, then don't worry about Hawking radiation from a black hole; the entire black hole vacuum becomes unstable."

The underlying physics of wormholes was not in doubt, the researcher argued. The real challenge was in explaining how to engineer wormholes big enough to be of practical use.

Cambridge astrophysicist Stephen Hawking is amongst those researchers who have pondered the question of wormholes.

In the 1980s, he argued that something fundamental in the laws of physics would prevent wormholes being used for time travel. This idea forms the basis of Hawking's Chronology Protection Conjecture.

[SirNitram]

Suck it Orion's Arm. Suck it long, suck it hard.

[Drunk Monkey]

Call Doc Broen hell give ya a time machine that looks like a DeLorian

[wolveraptor]

Ah, what a let down.

[Einhander Sn0m4n]

Good. I never liked time travel much anyway. I'm glad the Universe agrees with me

[Guardsman Bass]

Bah, so much for our chance of a galaxy-spanning united civilization 10-15,000 years from now. Guess we'll have to place our bets on life expansion.

[Molyneux]

Who gives a damn about time travel? I just want FTL. Hell, I'd settle for an infinite lifespan (with the option of committing suicide) and a long-range ship...

[Chmee]

Are we even close to having the technology to test this kind of theory? Definitive 'we've proved it won't work' statements seem as grossly premature as 'we're sure we can do it' statements, and are reminiscent of 1930's pronouncements that any aircraft passing the sound barrier will surely disintegrate ....

[wolveraptor]

Didn't they find this paper on that site for as-of-yet unpublished scientific articles, meaning it hasn't yet been peer-reviewed?

[GrandMasterTerwynn]

Didn't they find this paper on that site for as-of-yet unpublished scientific articles, meaning it hasn't yet been peer-reviewed?

One of the articles was based on work that has been published and peer-reviewed. And the fact that two independent groups are publishing papers adding credence to the notion that wormholes are a bad way of circumventing time and the speed of light should tell you something.

And this isn't really anything Earth-shattering. The equations describing wormholes have always worked out in a way that they'd be fantastically unstable without the addition of large quantities of exotic matter with negative mass. This just lends more weight to the likelihood that wormholes would be worthless time machines and space travel devices.

[Lord Zentei]

Who gives a damn about time travel? I just want FTL. Hell, I'd settle for an infinite lifespan (with the option of committing suicide) and a long-range ship...

The latter would probably be a better idea. That way you get to choose between limitless loafing and space travel rather than just space travel. Just remember to take enough pr0n for the trip and you are all set.

As for the wormholes, FTL invites similar causality problems as time travel, so this probably rules out FTL with wormholes too.

[Molyneux]

Who gives a damn about time travel? I just want FTL. Hell, I'd settle for an infinite lifespan (with the option of committing suicide) and a long-range ship...

The latter would probably be a better idea. That way you get to choose between limitless loafing and space travel rather than just space travel. Just remember to take enough pr0n for the trip and you are all set.

As for the wormholes, FTL invites similar causality problems as time travel, so this probably rules out FTL with wormholes too.

Drat..of course, FTL *and* an infinite lifespan would be best, but still, I'd like to not have to wait five hundred years or so to send a birthday card back to Earth.


On a somewhat-related topic...has anyone heard of the J.S. Bell Experiment and thought it might be used to make a primitive ansible? I don't know nearly enough of the technical stuff to know if it's plausible or not...

[Kuroneko]

No. EPR/Bell results show a relationship between measurements of entangled states. Locally, it is still random noise, and hence useless for communication.

[Molyneux]

No. EPR/Bell results show a relationship between measurements of entangled states. Locally, it is still random noise, and hence useless for communication.

I normally try to avoid posts with no real content to them, but...

DAMNIT! I was really hoping that'd be feasible. -_-
Even if true FTL is impossible, an ansible would be incredibly nice. Granted, you can't use it while travelling at relativistic speeds (time distortion would make it a very strange conversation), but it'd be nice to at least be able to talk from planet to planet without a delay of hours or years...

[GrandMasterTerwynn]

No. EPR/Bell results show a relationship between measurements of entangled states. Locally, it is still random noise, and hence useless for communication.

I normally try to avoid posts with no real content to them, but...

DAMNIT! I was really hoping that'd be feasible. -_-
Even if true FTL is impossible, an ansible would be incredibly nice. Granted, you can't use it while travelling at relativistic speeds (time distortion would make it a very strange conversation), but it'd be nice to at least be able to talk from planet to planet without a delay of hours or years...

In any universe where FTL communication is feasible, then FTL travel is too, since it can be abstracted into you conveying some sort of information from one place to another. (The difference being in whether the information is encoded on modulated electromagnetic pulses, or in complex arrangements of baryonic matter.)

In this universe, however, FTL travel isn't feasible. So, it naturally follows that FTL communication isn't feasible either.

[Molyneux]

No. EPR/Bell results show a relationship between measurements of entangled states. Locally, it is still random noise, and hence useless for communication.

I normally try to avoid posts with no real content to them, but...

DAMNIT! I was really hoping that'd be feasible. -_-
Even if true FTL is impossible, an ansible would be incredibly nice. Granted, you can't use it while travelling at relativistic speeds (time distortion would make it a very strange conversation), but it'd be nice to at least be able to talk from planet to planet without a delay of hours or years...

In any universe where FTL communication is feasible, then FTL travel is too, since it can be abstracted into you conveying some sort of information from one place to another. (The difference being in whether the information is encoded on modulated electromagnetic pulses, or in complex arrangements of baryonic matter.)

In this universe, however, FTL travel isn't feasible. So, it naturally follows that FTL communication isn't feasible either.

Ahem...we have yet to find a feasible form of FTL travel. It does not follow that there are no ways to circumvent the speed-of-light limit - we just don't know how to do it yet. I really hope that we do, though.

[GrandMasterTerwynn]

I normally try to avoid posts with no real content to them, but...

DAMNIT! I was really hoping that'd be feasible. -_-
Even if true FTL is impossible, an ansible would be incredibly nice. Granted, you can't use it while travelling at relativistic speeds (time distortion would make it a very strange conversation), but it'd be nice to at least be able to talk from planet to planet without a delay of hours or years...

In any universe where FTL communication is feasible, then FTL travel is too, since it can be abstracted into you conveying some sort of information from one place to another. (The difference being in whether the information is encoded on modulated electromagnetic pulses, or in complex arrangements of baryonic matter.)

In this universe, however, FTL travel isn't feasible. So, it naturally follows that FTL communication isn't feasible either.

Ahem...we have yet to find a feasible form of FTL travel. It does not follow that there are no ways to circumvent the speed-of-light limit - we just don't know how to do it yet. I really hope that we do, though.

Our standard model of the universe works very well to predict what we've observed in it. There are special circumstances where the speed of light can be violated, but none of them can convey information. Unless our understanding of the universe is glaringly, fundamentally wrong, then it is absolutely impossible to go send information faster than the speed-of-light.

[Archaic`]

Unless our understanding of the universe is glaringly, fundamentally wrong, then it is absolutely impossible to go send information faster than the speed-of-light.

It wouldn't be the first time. Flat earth...earth as the center of the universe...biblical creation...all seemed to explain things perfectly at the time, all ended up being very very wrong.

[Lord Zentei]

Unless our understanding of the universe is glaringly, fundamentally wrong, then it is absolutely impossible to go send information faster than the speed-of-light.

It wouldn't be the first time. Flat earth...earth as the center of the universe...biblical creation...all seemed to explain things perfectly at the time, all ended up being very very wrong.

Flat Earth and Biblical creation never seemed to explain things in a scientific sense of the word. Flat earth was demolished by the ancient Greeks, Biblical creation is not a scientific theory at all.

There is no reason to suppose that FTL is possible. That doesn't mean that it isn't possible of course, just that that is the way to bet.

[wolveraptor]

I don't pretend to know anything about particle physics, but what about tachyons? Theoretical particles that obey Einstein's lightspeed limit, but from the other side: they can't move any slower than 180,282 miles per second, without suffering the same effects that regular particles do when trying to move at the speed of light.

[Junghalli]

There is no reason to suppose that FTL is possible. That doesn't mean that it isn't possible of course, just that that is the way to bet.

Yes, but we can still hope.

[Lord Zentei]

I don't pretend to know anything about particle physics, but what about tachyons? Theoretical particles that obey Einstein's lightspeed limit, but from the other side: they can't move any slower than 180,282 miles per second, without suffering the same effects that regular particles do when trying to move at the speed of light.

Tachyons are completely and utterly speculative. They were concocted as a "thought experiment" as in "IF there were particles whose speed was greater than that of light, what would their properties be?"

No Tachyon has ever been observed. No theory of physics predicts or requires their existance. Tachyons do NOT exist.

Anyway, they would not be able to carry a signal even if they existed.

[GrandMasterTerwynn]

Unless our understanding of the universe is glaringly, fundamentally wrong, then it is absolutely impossible to go send information faster than the speed-of-light.

It wouldn't be the first time. Flat earth...earth as the center of the universe...biblical creation...all seemed to explain things perfectly at the time, all ended up being very very wrong.

Umm, no. Those were philosophical notions that were made to fit "common-sense" observations about the world made by ignorant primitives who had few tools at their disposal to observe and measure the world with, or were made up to satisfy man's deep-set egocentrism.

Our understanding of the universe is reliant on objective mathematical expressions and equations, not the sophistry of the ancients. We have much better tools at our disposal to measure and observe the universe with. And, our observations fit very well with our theories. And we can use our theories to accurately predict and model what goes on in our universe.

I would daresay that the odds of our understanding of the universe being proven as completely wrong as the notion that an invisible sky wizard created the Earth 6000 years ago is about the same as the odds that everyone on this board will take up sacrificing virgins to the planet Neptune.

[Junghalli]

I would daresay that the odds of our understanding of the universe being proven as completely wrong as the notion that an invisible sky wizard created the Earth 6000 years ago is about the same as the odds that everyone on this board will take up sacrificing virgins to the planet Neptune.

It doesn't have to be completely wrong, we just have to find a loophole or something we can bend.

[Sharpshooter]

Silly fools - don't they know Dave Anez has proved that it's possible?