Adam Turner
Illumin Article
The Alcubierre Warp Drive: Shattering Universal Speed Limits
Abstract
In 1994, Miguel Alcubierre brought forth the highly speculative idea for a fasterthan-light warp drive that would allow humans to travel between galaxies within a matter
of weeks. This shattered all preconceived notions of space travel and drove NASA scientists
to begin testing ways to improve and implement a warp drive device. There are, however,
many consequences and stipulations to superluminal (faster-than-light) travel.
Introduction
Since Einstein released his theory of special relativity in the early 20th century, the
scientific community as a whole has accepted the universal “speed limit” as the speed of
light, c. In other words the speed of light must be the same in all reference frames and no
information, or object, can travel faster than the speed of light with respect to its local
surroundings. Another consequence of special relativity is that the amount of energy
needed to accelerate an object to the speed of light grows exponentially to infinity as the
object approaches speed c. This is somewhat of a bummer for those who dream of
exploring the entirety of the Milky Way and other galaxies, as the Milky Way alone spans
more than 100,000 light years.
In 1994, however, Miguel Alcubierre published a paper [1], on the possibility of
faster-than-light travel using Einstein’s general relativity equations, which still followed the
speed limit dictated by special relativity. Since then, a few bold scientists have begun
testing the possibility of a warp drive, a technological advancement that could potentially
transport humans across galaxies in a matter of weeks.
Principle
The Alcubierre drive works around the limits of special relativity by the idea of
bending space-time, which Einstein allows in general relativity. As NASA states in [2],
Alcubierre’s warp drive creates an expansion of space behind the object and a contraction
of space in front, as shown in Figure 1. The best way to grasp this idea is to think about a
person moving on a motorized walkway similar to the ones at airports. If someone is
walking 5MPH before they encounter the walkway and they keep the same pace once on
the walkway, then really they have maintained their original velocity (5MPH), but are
moving much faster with respect to everything outside of the walkway. If the individual
conducted experiments in his local surroundings inside the walkway, he would find his
velocity to be 5MPH. The warp drive creates this motorized walkway and allows the
spacecraft to travel on it without breaking any of Einstein’s rules. In Figure 1, expanding, or
“pulling”, space-time behind the ship and contracting it in front creates the “walkway”.
Another way to think of this is if you are on a carpet and you want an object on the opposite
side of the carpet. Rather than walking towards the object, you could just create a
mechanism to pull the carpet out from behind you, which would result in the object being
pulled towards you. There is no acceleration or movement needed on your part, so no
universal rules are being broken.
Figure 1: Warp Drive contracting space in front and expanding behind.
Physicists believe that a spacecraft would be able to warp space around it faster
than the speed of light due to inflationary theory, part of which describes how space
expanded at a rate faster than light’s velocity during the big bang. The entire fabric of the
universe was significantly more condensed at the time of the big bang and, within seconds,
expanded to a scale slightly smaller than we know today. Because space-time was able to
expand this rapidly without any “speed limit”, scientists believe we could naturally warp
space-time in a similar fashion today. There are, however, a few complications that come
with expanding and contracting space-time, the most of important of which is energy.
Energy
The amount of energy needed to warp space-time and transport an object across
our solar system was originally estimated to be on the order of the entire mass-energy of
the universe, Broeck [3] describes. More recently, Harold "Sonny" White of NASA's Johnson
Space Center predicted the amount of energy needed to only be on the order of the massenergy of Jupiter. This improvement, as told by Moskowitz [4], came from new design
geometries of the warp drive as well as a proposition to regulate and modify the energy
amount being put into creating a warp bubble. While the mass-energy of Jupiter still seems
like an unachievable amount of energy, many scientists believe that more improvements to
warp drive designs like White’s could reduce the energy requirement to a more reasonable
amount.
Furthermore, the warp drive would need to use negative energy, a concept still
being argued within the scientific community. Classical physics does not allow for negative
energy levels, while the rapidly developing ideas of quantum physics dictate that negative
energy is a possibility, shown in [2]. Dutch physicist Hendrick Casimir predicted an effect
that would hint at the existence of negative energy called the Casimir effect, as described in
[5]. He believed that if you could create “pressure” differences between parts of the
quantum field (a constantly persisting field all around us), then you could create a force
from negative energy. To test this, physicist Steve K. Lamoreaux created an experiment
involving two uncharged metal plates (Casimir Plates) in a vacuum, as shown in Figure 2.
Lamoreaux set the plates apart by a nanometer-sized gap and proceeded to decrease the
gap size. As the two plates closed in on each other, the longer waves of the quantum field
could no longer fit in the gap.
Figure 2: Pressure differences between Casimir Plates
This created a “pressure” difference between the plates, which pushed them
together. This pushing force can be thought of as a form of negative energy. While
physicists have many ideas for where this pushing force emanates from, the most popular
theory behind the Casimir effect is the existence of negative energy, shown in [2]. Even if
we do prove ways to create negative energy, there is still much work to be done to enable
us to successfully harness its use.
Consequences
Assuming that scientists fully confirm the idea of negative energy and any other
speculative theories that accompany the function of the Alcubierre warp drive, there are
some major consequences to traveling across the universe in a bubble of negative energy.
One problem stems from the knowledge that space isn’t really as “empty” as people think it
is. There are plenty of high-energy particles that are constantly shooting around the
universe. As the warp drive travels across space, these high-energy particles would get
swept into the warp bubble. This issue arises when the warp drive stops at its destination.
All of the high-energy particles that were collected on the trip must now go somewhere,
and it is theorized that they would be released in a cone in front of the ship, as described in
[6]. The amount of particles gained on the journey is proportional to the length of the trip,
and there is no physical limit to the total amount of particles picked up by the bubble. This
is quite unfortunate for anything in the way of the high-energy beam, as the amount of
particles gathered on an intergalactic trip could potentially have enough energy to
obliterate a planet or even an entire star system. It would be a shame to discover a planet
suitable for human life only to destroy it on arrival.
An additional paradox with the warp drive appears when addressing the problem of
creating a negative energy bubble that warps space around it faster than the speed of light.
Trying to “turn off” the bubble from the inside once it is initiated is impossible if the edge of
the bubble is warping space faster than the speed of light. In other words, the pilot cannot
send a “signal” to the edge of the bubble because no signal would be able to move fast
enough to reach the front of the bubble. The only way someone could stop the spacecraft
would be from a station already placed that the destination. In the same way that railroads
need infrastructure and loading platforms, Alcubierre warp drives need external assistance
at the end of their journey. In this way, we are still limited in space travel to how fast we
can set up warp stations at destinations.
Feasibility and Development
As of now, Harold White and his team at NASA continue to attempt proving the
concept of the Alcubierre warp drive. White has engaged in an experiment, as shown in [7],
that allows him to measure fluctuations in space-time. If he turns on his prototype warp
drive and measures a difference in space-time length, he would be able to turn a purely
theoretical idea into a more practical one. Currently, the imprecise tools of today’s
technology limit him in his quest for knowledge. His experiment, though, is part of a much
larger dynamic within the physics community. Finding the existence of negative energy and
the ability to warp space-time may have many different repercussions for how we view the
universe as a whole. For example, we may not even need a warp drive for intergalactic
travel if we are able to create short cuts and tunnels within the fabric of the universe.
It is safe to say that the Alcubierre warp drive is still very much a speculative idea. In
fact, people question if humans could even survive in a bubble of negative energy, let alone
travel across thousands of light years in one. In the event that the theories that support a
warp drive are proven, getting a working prototype into space may easily take more than a
century.
Conclusion
While the Alcubierre warp drive still has much to endure to become a practical
solution to superluminal travel, it seems to be the most viable. When Alcubierre published
his paper in 1994, he shattered the perpetuating idea that a universal speed limit was the
end-all-be-all of space travel and opened a door for new types of thought. The fact that this
idea is only 10 years young and that top scientists improve it year by year gives the
community hope that huge developments are still to be made in this field. The practical
application may not be there yet, but the strength that Alcubierre’s theory has shown so far
has been more than impressive and gives hope to many who dream of exploring the
universe.
[1] M. Alcubierre “The warp drive: hyper-fast travel within general relativity” Classical and
Quantum Gravity, Volume 11, Number 5 (May 1994)
[2] NASA, Glenn Research Center “Ideas Based on What We’d Like to Achieve”
http://www.nasa.gov/centers/glenn/technology/warp/ideachev.html
[3] C. Moskowitz, “Warp Drive May Be More Feasible Than Thought, Scientists Say”
Space.com 17 September 2012
[4] C.V.D Broek “Alcubierre’s warp drive: Problems and prospects” 3 Feb 2000
http://scitation.aip.org/content/aip/proceeding/aipcp/10.1063/1.1290913
[5]”What is the Casimir Effect?” Scientific American 22 Jun 1998
[6]R. Whitwam “The downside of warp drives: Annihilating whole star systems when you
arrive” ExtremeTech 16 November 2012 http://www.extremetech.com/extreme/140635the-downside-of-warp-drives-annihilating-whole-star-systems-when-you-arrive
[7] G. Dvorsky “How NASA might build its very first warp drive” io9. 26 November 2012
http://io9.com/5963263/how-nasa-will-build-its-very-first-warp-drive