The original question was: Is this f’real?
Astronomer: The Alcubierre spacetime metric is named after a Miguel Alcubierre, a physicist who was also a Star Trek fan. It describes a type of bubble in space, where you could put, for example, a spaceship named USS Enterprise. Within the bubble space is isn’t doing anything weird, but in front of the bubble you scrunch up space and behind the bubble you stretch it out. If you could create space that was warped in this particular way, you could sit in your spaceship inside the bubble and move space around you faster than light in a way that would make it seem like you’d traveled at speeds faster than light. In reality, only the space itself would have travelled faster than light, which doesn’t break the speed limit rules imposed by relativity.
Bend some space like this and you can head for the second star to the right, and go straight on till morning!
The Alcubierre metric is a real solution to Einstein’s equations, which describe the ways in which space is allowed to bend or warp. There is no theoretical reason to think space couldn’t bend in this way, except for one very major problem. In the equations that describe the Alcubierre metric, one of the mass terms has to be negative for things to work out.
Know where I can get some negative mass? Didn’t think so. Negative mass, which is fundamentally different than anti-matter, would experience gravity as a repulsive force. Too bad nobody has ever discovered any negative mass floating around out there or made any substantial amount it. You can make really tiny amounts of negative mass/energy for very short periods of time in the lab, by “borrowing energy from the uncertainty principle,” but it’s not clear this could be scaled up to the macroscopic level like it would need to be to create a useful warp bubble.
It’s probably best negative mass doesn’t exist, because it’s incredibly creepy! For example, imagine you had a chunk of normal mass and a chunk of negative mass in space. The negative mass would fall towards the regular mass, but at the same time create “repulsive gravity” which would then push the normal mass away. Lather, rinse, repeat, and the you could theoretically accelerate those two chunks off into the stars forever. This smells suspiciously like perpetual motion, and would break the well established principle of conservation of energy. Given that, it’s understandable that we’re not packing the SPF 5000 for our super fast trip to Alpha Centauri Bb.
Physicist: It is for real, but don’t go reserving flights. There has been some theoretical research into Warp drives for about 20 years starting, not surprisingly, within months of the end of TNG. Back in the day Einstein figured out how mass/energy and the curvature of spacetime relate to each other with the narcissistically named “Einstein field equations“. These equations tell you how spacetime will be stretched and curved in the presence of a distribution of matter (for example, put a bunch of matter in one place, and spacetime will “pucker” in such a way that we get gravity). But these equations can be turned on their head; if you want spacetime twisted up in a particular way, you can find out how matter and energy need to be arranged to make that happen.
By bending spacetime in a particular way you can make it so that locally you move slower than light, but that the overall effect is faster-than-light travel. The arrangement of matter and energy that allows for this is unfortunately impossible. This diagram is from page 145 of “Gravity”, by Hartle.
Warp drive research always hinges on the idea that we should be able to arbitrarily manipulate stunning amounts of energy, and moreover, that a hell of a lot of that energy can be negative (essentially, “magical freeze-ray” powered warp drives). To date, we haven’t been able to isolate negative energy independent of a burst of positive energy (in any form), and there have been a few arguments (not proofs) that there may be an uncertainty-principle sort of thing that forces this to always be the case. Negative energy and matter carry with them an amazing array of fundamental issues. For example, if you bring matter and anti-matter together you get a big boom, resulting in a big increase in entropy (as light and new particles fly in every direction), but if you bring matter and negative-matter together they just quietly blink out, resulting in a big decrease in entropy (which is a thermodynamic no-no).
But! Assuming that negative energy can be harvested (even in theory), and very carefully controlled and manipulated in spectacular ways, and if a number of very fundamental theoretical issues can be ironed out, then this is totally a way to travel faster than light in a very Star Trek kind of way (as opposed to a BSG “jump drive“). Warp drives have been in the news a bit recently because it was shown that there are “spacetime geometries” that require less of the very-probably-impossible negative-matter than was originally thought (presumably, also because warp drives are awesome). This is a little akin to saying “my unicorn powered wish-making machine is now more feasible, because the unicorns can be any color, not just blue”.
For most physicists the Alcubierre drive is a cute tool for teaching general relativity, but in application smells a lot more like perpetual motion and anti-gravity machines than a device we’re ever likely to see.
There are some hopeful legit physicists, but not many.
Why would a clump of negative mass fall towards something with positive mass? I’d think that negative mass and positive mass would just repel each other, since for both masses your m_1*m_2 term would be negative in the gravity equation.
What would appear to be going on from the perspective of an outside observer witnessing a ship using an alcubierre warp drive?
Since when did an astronomer join this blog?
I’ve never heard of the Alcubierre warp drive before, and that is one of the reasons why I pop in here to get myself up to speed on such matters.
So if matter and antimatter explode, and matter and negative-matter zero sum, what would negative-antimatter do?
It would “sum to zero” with anti-matter.
Where does negative matter and negative anti-matter exist….?????
In my opinion, you can’t have “negative matter.” You can compare it to apples- you either have (for example) one or more apples, or no apples. You can’t have a negative apple!
An Alcubierre warp drive could contradict existing laws, like relativity (and its connection to time travel), and thermodynamics (in terms of conservation of energy). Besides, how could you amass enough energy to power this sort of device for a practical amount of time, say, a few days, or even for one minute?
Even if the warp drive were theoretically possible, the amount of finances and energy needed to make it possible would probably be too impractical for it to be actually built.
The momentum of a mass is mass * velocity. With negative mass and positive velocity, the momentum is negative.
The momentums of the positive mass and the negative mass would cancel out, so there would be no net energy change.
So they would accelerate “without limit” (excepting decay of various sorts), but it doesn’t violate conservation of energy, because the net energy of the system remains the same.
Work through the equations if you doubt.
This is so cool! One of my classmates worked with Dr. White at an internship with NASA, looking at (from what I recall) the basics of getting a high enough energy density for this to work. Still a long ways off, but warp drives in the making.
So how would you build it? With the exotic matter on the top or the bottom? Maybe left of the box of tachyons?
As far as I know there are no serious ideas behind how to build it at all.
Casimir effect is caused by a device consisting of two surfaces that are separated by a distance that defines the energy height of the quantum fluctuation in the vacuum. By placing many (>10**23) such mirrors together you would have a stiff sponge like material that would have to form a donut several miles across to contain the 1900 pounds of the resulting negative energy. Actually there was an example of a craft with that consistancy found by an air force pilot in pursuit of a UFO. The craft described by the pilot was that of fine spongelike appearance. This was reported about the 1990′s.
Whoa, Cashme no reason to bring UFO’s into this. For the small % of UFO sightings that cannot be easily explained many of them come in all shapes and sizes and appearance, including sponges.
It is not what these objects look like it’s what they DO that makes them enigmatical. There are equations that suggest these objects use energy in a similar way to us except it is produced within a very much smaller volume (and therefore that much more advanced). But the real problem is the enveloping ‘energy field’ that is needed to protect the occupants (and the craft) from both radiation and maneuvers but even here negative mass isn’t the answer because of the (reported) positive, and sometimes destructive, effect on surroundings.
Never mind, Cashme, let us know when you’ve constructed all those mirrors!
Would it be a simpler problem to use the drive to increase the power and efficiency of a reaction engine by using it to increase the speed of the propellent? Move the propellent faster, the more difficult problem of moving the entire ship can wait until the technology matures.
@Bob
I thought the amount of energy required to power it up would be all one required.. that is unless acceleration of mass is used to increase the warping effect by increased mass. Either way I would have thought that you would only need as much energy required to compensate for resistance in the accelerated mass and therefore the only real energy problem comes from powering the thing up.. or rather ‘engineering’ the negative mass and accelerating it (if required) (as well as the positive mass) which apparently merely 1,600 pounds worth of mass/energy for something the size of voyager. I cannot recall how much uranium that is but yeah.. sounds better than scooping up a whole Jupiter to just squeeze into a reaction chamber. Or so I’m led to believe.. :/
the kinetic energy of the accelerating negative matter would be just as negative as the KE of the positive matter is positive.
the energies (sp. ?) would cancel out.
that is, in Newtonian physics.
I don’t know what it would do in general or special relativity, or in Quantum mechanics.
but yeah it doesn’t violate conservation of energy is Newtonian physics.
the accelerations will be the same (provided they have the same magnitude of mass, and there is no other masses in the system), so if they start at 0 velocity, they will always have the save velocity.
KE – 1/2 m v^2, so plug in the values and you get the energies being negative of the other,
and it sums to zero.
oh, someone already posted that.
nvm then.
What kind of gravity will you have inside the bubble? The original gravity when you initiated the ‘trip’ or you can generate your own gravity? and another question , as the ship deformates the space I understand that it won’t be affected by any asteroids or radiations in its way while in the bubble so…can the ship traverse the core of a planet , a star, dump into the oceans without being affected by the deep, even enter inside an active volcano?…