What hypothetical properties would negative energy have?

[Lren Zvsm]

I would like to know about the hypothetical properties of hypothetical negative energy--most especially the properties that would be useful for a science fiction writer to know. If such energy existed, could it be used in a drive for space craft? An FTL drive? For a weapon? A safety device? Would it suggest the existence of other universes? And so forth.

 

[mfb]

Most importantly it would probably destroy everything in the universe where it can exist.
If a process doesn't violate any conservation laws it happens with some probability. If everything has positive energy then a vacuum is the lowest energy state - nothing can be produced there. If there are things with negative energy then these plus things with positive energy can appear spontaneously. This should happen everywhere and all the time, making a universe with ordered structures implausible.
There might be some way to create conditions to avoid this, or you can simply ignore this issue. The results can depend on that, however.

If things with negative energy are only made under special conditions in the lab then you can use that process as unlimited energy (and propulsion) source: Just throw away the negative energy parts, keep the positive energy parts.

The Alcubierre drive is a hypothetical concept that might allow something that looks like FTL (without anything actually moving faster than light) if you can create extreme negative energy densities.

Would it suggest the existence of other universes?

No.

 

Negative energy is not that pervasive in sci-fi, and especially not in detail, but given that it's hypothetical, you can use it for whatever narrative purpose you like.

So, it can buttress wormhole entrances. It could be used for defense, to deflect energy beams, and even projectiles if the density is high enough. It might be handwavium for some kind of time travel or time status device. You can make it a drive by 'pushing' against the fabric of our regular universe.

Basically, as @mfb notes, it's not 'scientific' and as such you can utilize it pretty much anyway you like in a story

 

[essenmein]

It is not so hypothetical... Negative energies are OK with QFT and for example the Casimir effect can create negative energy density.

Gravity is another interesting one as described in the first section:

https://en.wikipedia.org/wiki/Negative_energy

 

Good pickup, @essenmein, my comment was more aligned with sci-fi aspect of "hypothetical" negative energy as per the OP, but did not make that clear

 

[essenmein]

Good pickup, @essenmein, my comment was more aligned with sci-fi aspect of "hypothetical" negative energy as per the OP, but did not make that clear

I looked into negative energy quite a bit as I wanted my FTL to sound semi plausible, although I didn't really end up using anything specifically as it gets wonky pretty quick... Just lots of EM and a thing that makes negative energy, voila jump drive, shut up don't ask too many questions it works. lol.

 

I looked into negative energy quite a bit as I wanted my FTL to sound semi plausible, although I didn't really end up using anything specifically as it gets wonky pretty quick

It is a fine line, isn't it. Most readers want a story, not a physics textbook, and while The Martian highlights that good science can sell, the gazillion more books purchased by lovers of Iain M. Banks, Peter F. Hamilton, Richard Morgan, etc., which have speculative, not in our universe, 'science' in the fiction shows that semi plausible gets you by more often than not.

I've just re-read Alastair Reynolds's House of Suns, and it does not have FTL, making time dilation a major plot lever, but it does have a ton of other impossible tech (stardams being one - that's a Dyson sphere which contains a supernova!) that you don't even notice because the focus is on the characters and the story being told.