Behind the Warp Drive Hype

I’m sure you’ve seen the headlines. In case you’ve been hiding under a rock for the last few weeks, or at least tuning out the news (understandable, given that this is election season), here is a sampling:

But it all traces back to this article:

The media frenzy was triggered by comments made by physicist Dr. Harold “Sonny” White of the Eagleworks Lab at NASA’s Johnson Space Center at the 100 Year Starship 2012 Symposium, held September 13-16, 2012 in Houston. The event, branded with the theme “Transition to Transformation … The Journey Begins,” featured numerous guest speakers, mostly scientists, but also including Star Trek actors Levar Burton and Nichelle Nichols (who has a long and successful history of working with NASA on initiatives to recruit women and minorities into science and technology fields).

(This is the second such symposium. The first was held in Orlando in October of last year.)

Backed by the Dorothy Jemison Foundation for Excellence, the Foundation for Enterprise DevelopmentIcarus Interstellar, and grants from DARPA and NASA, the 100 Year Starship Initiative is a non-government entity founded in January of this year with the goal of persuing and encouraging public and private initiatives to make interstellar space flight achievable within a century.

So, what did Dr. White say at this symposium to create such buzz?

“There is hope.”

Well, he said a bit more than that, but explaining requires a bit of back story.

In the Beginning, there was Alcubierre

For many decades, the bending of space-time has been a conceit long favored by science fiction writers as a workaround for dealing with the daunting (and, literally, astronomical) distances involved in interstellar space flight. But, within the scientific community itself, the idea of “warp drive” had been mainly a topic of idle speculation, with few scientists finding the prospect realistic as a practical means of spacecraft propulsion.

Then, in 1994, Mexican theoretical physicist Miguel Alcubierre published a paper 1 outlining what has come to be known as the Alcubierre drive, the first example of a physicist earnestly tackling the mathematical heavy lifting of exploring the concept in depth. In the paper, Alcubierre defined a space-time metric (and its associated stress-energy tensor) in which space in front of the ship is contracted, and the space behind the ship is expanded. These contracting and expanding regions of space-time propagate as waves, with the spacecraft riding along in a flat region inside this warp bubble, not moving with respect to the space in which it sits, and thus experiencing no inertial effects.

The Alcubierre Drive

Two dimensional slice of the warp bubble generated by the Alcubierre Drive (Image courtesy of Wikimedia Commons)

What makes this conceptually possible is that at no point is the spacecraft itself moving faster than light with respect to the space-time manifold in which it is embedded. Such superluminal motion is of course forbidden by relativity. However, relativity does not forbid space-time itself from expanding or contracting faster than lightspeed. In fact, an important component of modern cosmology is the concept of “inflation,” a brief period during the beginning moments of the universe in which space-time expanded at a superluminal rate.

But, as intriguing as this is, there are problems with Alcubierre’s idea. First of all, while Alcubierre showed that it is indeed theoretically possible for such a warp bubble to exist, we still have no idea how to generate one. Krasnikov and Coule2,3 have argued that constructing such a field would require constructing the fields in motion such they are already moving at superluminal velocities. In other words, creating a warp drive requires the existence of a warp drive.

In 2002, a paper appeared4 arguing that it would be impossible for the crew of a ship utilizing an Alcubierre drive to send signals to the front of the warp bubble, rendering it impossible for them to steer or stop the ship.  A 2009 paper5 suggested that the crew of such a ship would be subjected to intense amounts of Hawking radiation; although, in this context, it might be more accurate to refer to it as Unruh radiation.

But, perhaps the biggest obstacle was one of energy. This problem was two-fold. One was a requirement for the creation of a region of intense negative energy density, a feat which would require the existence of some form of exotic matter with properties which, while not forbidden by the laws of physics, is not known to exist. The other aspect of the problem was one of magnitude. Pfenning and Ford6 estimated that the energy equivalent of -1064 kg would be needed, a magnitude greater than the estimated mass of the known universe. Furthermore, it was argued in the same paper that the exotic matter ring required to establish the needed negative energy density geometry would have to be an impossibly thin structure.

In a 1999 paper7, Chris Van Den Broeck tackled the issue of how much energy would be required to produce a warp bubble. By modifying the geometry of the bubble, he came up with a configuration which reduced the energy needed to transport a handful of atoms to roughly three solar masses. Krasnikov8,9 then built upon this work to reduce the energy requirements to just a few milligrams. (Remember, this is for generating a warp bubble containing just a TINY amount of matter.)

Dr. White’s Findings

A paper has yet to be published (or even pre-printed on arXiv.org) outlining Dr. White’s latest work, but in his presentation at the 100YSS conference, he revealed that his calculations show that by replacing the flat ring of exotic material with more of a toroidal shape, the energy requirements for a 10m warp bubble traveling at 10c would be reduced from the equivalent energy bound up in the mass of Jupiter to that of a mass of 500 kg. On top of that, he claimed that his calculations show that causing the intensity of the space warp to oscillate reduces the energy requirement even more.

“The math would allow you to go to Alpha Centauri in two weeks as measured by clocks here on Earth,” White said. “So somebody’s clock onboard the spacecraft has the same rate of time as somebody in mission control here in Houston might have. There are no tidal forces, no undue issues, and the proper acceleration is zero. When you turn the field on, everybody doesn’t go slamming against the bulkhead, (which) would be a very short and sad trip.”

“The findings I presented today change it from impractical to plausible and worth further investigation,” he told SPACE.com. “The additional energy reduction realized by oscillating the bubble intensity is an interesting conjecture that we will enjoy looking at in the lab.”

The lab? Yes, the lab. Dr. White has devised an apparatus to test this concept on a table-top scale at Johnson Space Center. Known as the White-Juday Warp Field Interferometer, this experiment is designed to look for perturbations in space-time on a scale of one part in 10 million. Not enough to propel a space craft, but enough to provide a proof of concept. If it works.

“Although this is just a tiny instance of the phenomena, it will be existence proof for the idea of perturbing space time-a “Chicago pile” moment, as it were. Recall that December of 1942 saw the first demonstration of a controlled nuclear reaction that generated a whopping half watt. This existence proof was followed by the activation of a ~ four megawatt reactor in November of 1943. Existence proof for the practical application of a scientific idea can be a tipping point for technology development.”

Somewhat similar to the Michelson-Morley experiment used to disprove the existence of the luminiferous æther in the late 19th century, the device can also be thought of as a scaled-down version of the interferometer experiments currently being used in attempts to detect gravitational waves, a phenomenon predicted by general relativity. The primary difference with the White-Juday Warp Field Interferometer is that one arm of the light path passes through a 1 cm diameter toroidal capacitor ring.

Of course, this ring will generate a region of positive energy density, not a region of negative energy density as needed by the Alcubierre drive concept. Nevertheless, if it works, it would be a splendid proof of the ability to manipulate space-time in an energy-efficient manner. And if anyone happens to have a few tons of negative energy density unobtainium on hand, I’m sure that Dr. White and his team would love to hear from them.


References:

  1. Alcubierre, Miguel (1994). “The warp drive: hyper-fast travel within general relativity”. Classical and Quantum Gravity 11 (5): L73–L77. arXiv:gr-qc/0009013. Bibcode: 1994CQGra..11L..73A. doi:10.1088/0264-9381/11/5/001
  2. S. Krasnikov (1998). “Hyper-fast travel in general relativity”. Physical Review D 57 (8): 4760. arXiv:gr-qc/9511068. Bibcode: 1998PhRvD..57.4760K. doi:10.1103/PhysRevD.57.4760.
  3. Coule, D H (1998). “No warp drive”Classical and Quantum Gravity 15 (8): 2523–2537. Bibcode: 1998CQGra..15.2523C. doi:10.1088/0264-9381/15/8/026.
  4. Natário, José (2002). “Warp drive with zero expansion”. Classical and Quantum Gravity 19 (6): 1157–1165. arXiv: gr-qc/0110086. Bibcode: 2002CQGra..19.1157N. doi: 10.1088/0264-9381/19/6/308.
  5. Finazzi, Stefano; Liberati, Stefano; Barceló, Carlos (2009). “Semiclassical instability of dynamical warp drives”. Physical Review D 79 (12): 124017.arXiv: 0904.0141. Bibcode: 2009PhRvD..79l4017F. doi: 10.1103/PhysRevD.79.124017.
  6. Pfenning, Michael J.; Ford, L. H. (1997). “The unphysical nature of ‘Warp Drive'”. Classical and Quantum Gravity 14 (7): 1743–1751. arXiv: gr-qc/9702026. Bibcode: 1997CQGra..14.1743P. doi: 10.1088/0264-9381/14/7/011.
  7. Broeck, Chris Van Den (1999). “A ‘warp drive’ with more reasonable total energy requirements”. Classical and Quantum Gravity 16 (12): 3973–3979. arXiv: gr-qc/9905084. Bibcode: 1999CQGra..16.3973V. doi: 10.1088/0264-9381/16/12/314.
  8. S. Krasnikov (2003). “The quantum inequalities do not forbid spacetime shortcuts”. Physical Review D 67 (10): 104013. arXiv: gr-qc/0207057. Bibcode: 2003PhRvD..67j4013K. doi: 10.1103/PhysRevD.67.104013.
  9. van den Broeck, Christopher “Alcubierre’s warp drive: Problems and prospects”. AIP Conference Proceedings 504: 1105-1110. 2000. Bibcode: 2000AIPC..504.1105V. doi: 10.1063/1.1290913.

For more information:

About Glen Mark Martin

MCSE-Messaging. Exchange Administrator at the University of Texas at Austin. Unrepentant armchair physicist.
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4 Responses to Behind the Warp Drive Hype

  1. Taha Ahmad says:

    “Of course, this ring will generate a region of positive energy density, not a region of negative energy density as needed by the Alcubierre drive concept.”

    I have been reading many articles on this and this is the first one that attempts to explain how the test will be run.

    My question is this: How are they able to test this theory with a region of positive energy density (or matter that does not violate the energy condition?)

    Does the breakthrough also involve removing the need for matter with negative energy density? If yes, then Dr. White should get a Nobel Prize for this.

    Thank you for this awesome post 🙂

  2. Details of the experiment have been scant (and I’ve included links to all I’ve found – note the two links to items authored by Dr. White under the “For more information” section), but I’ve seen nothing to indicate that Dr. White believes that he has eliminated the need for having a region of negative energy density. What he appears to be testing involves his ideas for reducing the magnitude of energy needed to create a temporary, localized deformation of space-time, albeit in not quite the configuration that would be needed to realize a functioning Alcubierre drive.

  3. Taha Ahmad says:

    Interesting and thank you for your quick reply.

    After reading a bit more, I am still confused by how he is able to run an experiment without using exotic matter and why that same methodology is unable to scale up to macro-level warps. Here is to hoping that we get more details about this in the coming months.

    So essentially, the biggest technical challenge, still seems to lie in creating or finding (for mining) exotic matter.

    If you do find some additional information, please email me at taha_29@hotmail.com and if I run across something, I will make sure to post it as a reply here.

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