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Will a sample of negative energy be produced by 2100?
Warp drives. Wormholes. Time machines. These exotic structures are the stuff of science fiction, but also have valid mathematical structures behind them in the form of spacetime "metrics" one can write down with the requisite properties.
There is one major physical issue standing in the way actually making them, however: all these possibilities require negative energy.
More specifically, relativists have devised a number of mathematical conditions that may be assumed regarding matter and energy, known as "energy conditions." Wormhole, warp-drive, and time-machine solutions to Einstein's equations essentially always require some substance that violates the "weak energy condition" (WEC), and generally others. Most simply, the WEC states that in the restframe of a material, its energy density is non-negative. (Technically the substance's pressure also must be sufficiently non-negative; see e.g. here for a brief description, and a good relativity text like this one for more gory detail, and here for a recent, interesting review.)
These energy conditions are generically violated at the quantum level, because quantum mechanics entails uncertainty in the energy of a system over a very short time period, so must allow very brief negative-energy fluctuations. But macroscopic amounts of negative energy do not appear possible with any particles or fields we know to exist.
On the other hand, it is somewhat unclear what fundamentally forbids negative energy. Negative energy particles would be bad news, as they would likely render low-energy particles unstable to decay into positive and negative energy ones – such a universe would not last long. But could we devise some strange substance that has the property, using something like the Casimir effect, that takes empty space and removes some energy from it? It sees plausible that negative energy is closely related to violations of the second law of thermodynamics, which would mean that it is very, very hard to violate. But maybe not impossible. "Violations" of the second law (downward movements in entropy) can happen if you wait long enough, or if you set up very, very careful initial conditions (see, e.g. here) So it does not seem impossible that with a high level of tuning a sample of negative energy could be made, though the author is not at all clear how...
So instead we ask:
Will a sample of negative energy material be created by the year 2100?
To be specific, we'll ask whether > 10 proton masses worth of negative energy will be created and confined to a volume of less than 1 cubic centimeter for longer than 1 microsecond, in such a way that during that microsecond there exists a volume of space that could be considered to have a mass of less than -10 proton masses. (As of 2017, the record for antimatter, an altogether easier substance to make, was about 300 proton masses.)
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