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Astronomy Without A Telescope – Warp Drive On Paper

30 Oct , 2010

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The Alcubierre drive is one of the better known warp drive on paper models – where a possible method of warp drive seems to work mathematically as long as you don’t get too hung up on real world physics and some pesky boundary issues.

Recently the Alcubierre drive concept has been tested within mathematically modeled metamaterial – which can provide a rough analogy of space-time. Interestingly, in turns out that under these conditions the Alcubierre drive is unable to break the light barrier – but quite capable of doing 25% of light speed, which is not what you would call slow.

OK, so two conceptual issues to grapple with here. What the heck is an Alcubierre drive – and what the heck is metamaterial?

The Alcubierre drive is a kind of mathematical thought experiment where you imagine your spacecraft has a drive mechanism capable of warping a bubble of space-time such that the component of bubble in front of you contracts bringing points ahead of you closer – while the bubble behind you expands, moving what’s behind you further away.

This warped geometry moves the spacecraft forward, like a surfer on a wave of space-time. Maintaining this warp dynamically and continuously as the ship moves forward could result in faster-than-light velocities from the point of view of an observer outside the bubble – while the ship hardly moves at all relative to the local space-time within the bubble. Indeed throughout the journey the crew experience free fall conditions and are not troubled by G forces.

Standard images used to describe the Alcubierre drive. Left: Want to make the Kessel run in 12 parsecs? No problem - just compress the Kessel run into 12 parsecs. Right: The Alcubierre concept can be thought of as a spaceship surfing on a wave of space-time. Images sourced from daviddarling.info.

Some limitations of the Alcubierre drive model are that although the mathematics can suggest that forward movement of the ship is theoretically possible, how it might start and then later stop at its destination are not clear. The mechanism underlying generation of the bubble also remains to be explained. To warp space-time, you must redistribute mass or energy density in some way. If this involves pushing particles out to the edges of the bubble this risks a situation where particles at the boundary of the bubble would be moving faster than light within the frame of reference of space-time external to the bubble – which would violate a fundamental principle of general relativity.

There are various work-around solutions proposed, involving negative energy, exotic matter and tachyons – although you are well down the rabbit-hole by this stage. Nonetheless, if you can believe six impossible things before breakfast, then why not an Alcubierre drive too.

Now, metamaterials are matrix-like structures with geometric properties that can control and shape electromagnetic waves (as well as acoustic or seismic waves). To date, such materials have not only been theorized, but built – at least with the capacity to manipulate long wavelength radiation. But theoretically, very finely precisioned metamaterials might be able to manipulate optical and shorter wavelengths – creating the potential for invisibility cloaks and spacecraft cloaking devices… at least, theoretically.

Anyhow, metamaterials capable of manipulating most of the electromagnetic spectrum can be mathematically modeled – even if they can’t be built with current technologies. This modeling has been used to create virtual black holes and investigate the likelihood of Hawking radiation – so why not use the same approach to test an Alcubierre warp drive?

It turns out that the material parameters of even so-called ‘perfect’ metamaterial will not allow the Alcubierre drive to break light speed, but will allow it to achieve 25% light speed – being around 75,000 kilometres a second. This gets you to the Alpha Centauri system in about seventeen years, assuming acceleration and deceleration are only small components of the journey.

Whether the limitations imposed by metamaterial in this test are an indication that it cannot adequately emulate the warping of space-time – which the Alcubierre drive needs to break light speed – or whether the Alcubierre drive just can’t do it, remains an open question. What’s surprising and encouraging is that the drive could actually work… a bit.

Further reading: Smolyaninov, I. Metamaterial-based model of the Alcubierre warp drive.

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J. Major
Member
October 30, 2010 2:17 PM

What about the energy requirements to do all this space-time compressing and expanding? I mean, if it were feasible within “normal” power generating that one might use on a spaceship that’s one thing, but if it turns out to be one of those “infinite energy is needed” situations then it kind of renders the practical application moot, no?

tacitus
Member
October 30, 2010 2:35 PM
It turns out that the material parameters of even so-called ‘perfect’ metamaterial will not allow the Alcubierre drive to break light speed, but will allow it to achieve 25% light speed – being around 75,000 kilometres a second. This gets you to the Alpha Centauri system in about a year or the Gliese 581 system in about five years, assuming acceleration and deceleration are only small components of the journey. I can’t believe you got this so wrong, Steve! Traveling at 25% of light speed to Alpha Centauri will get you there in 17.46 years not one and a bit years (i.e. 4.36ly / 0.25 not 4.36ly * 0.25). I guess we’re all allowed a brain fart every… Read more »
Bombadil
Member
Bombadil
October 30, 2010 4:09 PM

Maybe he’s already gone as far as to calculate the effects of time dilation? smile

gopher65
Member
gopher65
October 30, 2010 4:44 PM

You shouldn’t experience time dialation with an Alcubierre warp drive. So that’s not it. I think he just divided when he should have multiplied. It should have been “about 16 years and about 80 years”, rather than 1 and 4 respectively.

As to the Alcubierre warp drive only being able to do 25% of the speed of light due to practical limitations, that’s almost exactly what I said years ago when I heard about the ideasmile. It was my opinion at the time that the warp drive would be absolutely awesome for intra-system travel, but not really any better than more standard sublight drives (fusion rockets, laser powered solar sails) for interstellar travel.

mavrande
Member
October 30, 2010 5:01 PM

I realize that time dilation was a joke – but my understanding of the Alcubierre drive was that time dilation didn’t actually apply since the theoretical spaceship wasn’t moving through space, but was rather moving space. or something like that?

mavrande
Member
October 30, 2010 5:03 PM

Gopher65 beat me to the punch, and I was too busy looking up Krasinov tubes on Wikipedia to realize it. wink

gopher65
Member
gopher65
October 30, 2010 5:37 PM

I’m faster than a speeding Mavrande. And I can leap over tall… children. As long as they’re short. And they have to crouch down. And a springboard would be helpful.

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 30, 2010 6:10 PM
There are a number of thoughts I have about this. I speculate this might represent a departure between these optical analogues of spacetime physics. There are some very serious problems with these ideas of warp drives and wormholes. I will try to illuminate them after one important comment. The question is raised whether we can really “grab” spacetime and make this ripple. The Alcubierre warp drive relies upon being able to compress a region of space in the forwards region, thus reducing the effective distance on travels and creating a sort of gravitation, and expanding the spacetime region in the trailing region. One must be able to “grab” spacetime by some means. There is a big problem here… Read more »
Lawrence B. Crowell
Member
Lawrence B. Crowell
October 30, 2010 7:13 PM

One feature of the Alcubierre warp drive is that special relativity calculations do not apply.

LC

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
October 30, 2010 8:29 PM

The main problem with Alcubierre bubbles is AFAIU that they travel at the speed they are created. Since no one knows how to travel faster than light, no one knows how to make an Alcubierre bubble go faster than light. (Well, duh!)

Seems to me these models confirm this.

So this is no physical mechanism that gets you FTL drives. It is merely pointing out how doubtful that is, since it would imply a completely different physics than we know. See Scott Aaronson’s papers on the problems with time travel. (Which FTL effectively is for some light rays.)

Jason
Member
October 31, 2010 4:09 AM

Perhaps a phase-shifted electrodynamic thruster could be capable of doing much more than 25% of light speed just by applying correctly nowadays technologies.

Lawrence B. Crowell
Member
Lawrence B. Crowell
October 31, 2010 1:59 AM

That is another problem of course. The horizon structure of the warp drive prohibits the device (ship) at the center from being able to control it, which includes creating it.

The thing that is interesting about the Alcubierre warp drive and related structures is they permit us to theoretically examine the causal structure of physics and its relationship to the nature of quantum mechanics and its relationship to the structure of quantum mechanics.

LC

DrFlimmer
Member
DrFlimmer
October 31, 2010 3:25 AM

I remember a public talk of a physics professor about “the physics of Star Trek” (he also made talks about the physics of James Bond or football (soccer for the American people here) — the talks are VERY entertaining!). He also talked about the warp drive and said that “it would be theoretically possible. However, to compress 30 solar masses of energy, which are required for it to work, into the Enterprise is the problem of the engineers!” (Metin Tolan, TU Dortmund, Germany)

He also calculated that the Enterprise including all personnel weighs roughly 160kg !

grin

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
October 31, 2010 7:37 AM
The thing that is interesting about the Alcubierre warp drive and related structures is they permit us to theoretically examine the causal structure of physics and its relationship to the nature of quantum mechanics and its relationship to the structure of quantum mechanics. That is exactly right, I think. Given the energy problems you point out it looks like a gedanken experiment, IIRC it takes more energy than in the visible universe mass content to make one bubble with small enough walls (as given by the energy density required). But the models mentioned in the article makes this more accessible to actual verification and elucidation (making and testing more predictions), which points to a healthy physics area in… Read more »
ProfMOZ
Member
ProfMOZ
October 31, 2010 8:59 AM

Hi, carbon copieswink
Re: the speed of light barrier(!?)
Let us just be logical here… it is obvious, that either we apply known physical properties, or go beyond this barrier with new rules… The the Alcubierre warp drive thought model, used here, clearly lacks logic.
Einstein, the greatest carbon copy of them all, is right, a Lorentzian wormhole is possible. The only question is: HOW do we create, or find wormholes AND what kind of force do we apply to ride them?

Duncan Ivry
Guest
Duncan Ivry
October 31, 2010 10:50 AM
Steve Nerlich, your article is a good assessment of Alcubierre’s warp drive, especially the skeptical part — “on paper” etc. Because I just wanted to know, some time ago I started going rather intensively through pertinent articles, including that of Smolyaninov. It’s remarkable, how some authors bury supposed evidence in favor of warp drive being possible in piles of quotes of previous articles of their own and of others, where, if you look into, you will find the same, again piles of quotes of articles quoting again etc. The way down is accompanied by plain seems-promising-like statements, assessments assessing nothing, deceptive vocabulary (e.g. “engineering” when nothing can be engineered), and a small number of pseudo-proposals of physical experiments… Read more »
The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
October 31, 2010 3:04 PM

Perhaps the EU/PC might know something about this, as in the Star Trek universe, it is driven by circulating warp plasma. No doubt these jackasses also do believe this is ‘true’ science too!

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
October 31, 2010 3:21 PM

The following link is the original reference to this story that appears in the Journal
“Classical and Quantum Gravity” I.e. Alcubierre, Miguel, “The warp drive: hyper-fast travel within general relativity,” Class. and Quantum Grav., vol. 11, p. L73 (1994),

“It is easy to convince oneself that, if we define this relative speed as the rate of change of proper spatial distance over proper time, we will obtain a value that is much larger than the speed of light. This doesn’t mean that our observers will be travelling faster than light: they always move inside their local light-cones.”

This is why;

“The resulting distortion is reminiscent of the ‘warp drive’ of science fiction.”

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