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My understanding of the hypothesis is somewhat hazy, so I probably have gotten something wrong.

But as I understand it, the total energy density of the universe is either very small or exactly zero, because all of the positive energy is outweighed by negative energy—gravity, if I recall correctly.

The vacuum genesis hypothesis takes this idea a step further. We already know that energy spontaneously creates itself, but lasts for immeasurably short amounts of time (particles and antiparticles spontaneously appear in a vacuum). So what if the universe is like this? The beginning of the universe may have been a quantum vacuum that experienced quantum fluctuations, and boom. Lots of mass, but also (maybe) an equal amount of gravity. The total energy density of the system didn't change, so all the laws of physics are happy.

My question—could this principle be used by some Type III or IV civilization to create infinite energy? Whatever energy you create could be balanced out by the gravitational energy it creates, yes? Granted, I'm pretty sure there's no known way to even begin to do something like this, but is such a thing at least permitted within the laws of physics?

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  • $\begingroup$ This seems like it should belong in physics.se, otherwise its a "sure, why not?" answer based on your tags (eg lacking "hard-science") $\endgroup$
    – Marky
    Commented Aug 18, 2016 at 2:48
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    $\begingroup$ Quantum field theory suggests that the universe should have a massive mass-energy density. Observations indicate this isn't so. The discrepancy is a factor of 10^120. This is embarrassing. When the discrepancy is a multiple of one followed by 120 zeroes, something doesn't add up. The zero point bit derives from the idea that the vacuum can exist in a lower energy state. If a mechanism existed to extract this energy, while it wouldn't be infinite there would be lots & lots. There's no certainty physics does allow this. It's OK for science-fiction. $\endgroup$
    – a4android
    Commented Aug 18, 2016 at 4:18
  • $\begingroup$ @a4android Do you have a source for that? I like collecting things with big numbers, and 10^120 is too sweet to pass up! $\endgroup$
    – Cort Ammon
    Commented Aug 18, 2016 at 4:30
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    $\begingroup$ @CortAmmon the original absurd value is well-known as “the biggest error in phyeics”. See here to get started. $\endgroup$
    – JDługosz
    Commented Aug 18, 2016 at 5:25
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    $\begingroup$ This discrepancy is between a naive interpretation of quantum mechanics and the general relativity result calculated from measurements of the universes expansion. The discrepancy will likely disappear when a theory of quantum gravity comes along. $\endgroup$
    – Donald Hobson
    Commented Aug 18, 2016 at 7:04

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about zero-point energy

Here is an analogy. Consider a waterfall (or the drop of a river) generating power. When the water reaches the bottom of the ocean, you can't turn a waterwheel anymore, right?

But the water at the bottom of the deepest point in the ocean still has gravitational potential energy! It is feeling weight due to the Earth, and it's about 4000 miles from the center. In fact, since it only dropped 20 miles or so since it started in the mountains, it still has most of its potential energy untapped!

This is exactly the same concept. A potential is useless without a place to exploit the potential difference. There’s no drain at the bottom of the ocean; nor could there be since the Earth isn’t really a point mass at the center of its gravity field.

Running infinite debt

What you’re describing in the OP doesn’t seem to be anything like zero point energy, but is an observation that the total energy of the universe might be zero. How would that provide for infinite energy?

«Whatever energy you create could be balanced out by the gravitational energy it creates, yes?»

Yes. That is how the dark energy (if it's indeed the energy in empty space) is created as space expands. As I recall from Laurence Krauss’s book (IIRC the attribution), this is allowed because gravity has no fear of debt.

So can you do anything with that? Well… I don’t see anything. If you enlarge space you don’t get usable energy. Making use of gravity wells in the normal way, you will run out of stuff to throw into a black hole, and the potential is that of the event horizon, not infinite.

But consider this idea I came up with some time ago: imagine a future empty universe. Put two huge masses on opposite ends of a long string, and that string is so long that the expansion of space tries to carry them apart with more force than the gravitational attraction between them. The far end is essentially being lowered into an infinitely deep well, which is deeper than a black hole because you never reach the horizon.

In order for it to do work, you have to actually let it pull out more string. So this well is only infinite until you run out of string.

No matter how clever you are, there is still only a finite amount of useful potential up to your cosmic horizon.

beyond normal physics

Can they create new pocket universes? Can they create wormholes or acheive FTL travel? There may be unlimited energy sources there, too. Now you keep using energy until you “pollute” your own universe with too much entropy and reach limits there… so dump your waste into a parallel universe or through a wormhole beyond your cosmic horizon, or somesuch.

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  • $\begingroup$ Alright, you cannot enlarge space to get usable energy. But if the universe originated from quantum fluctuations, usable energy spontaneously came into being alongside dark matter, correct? Why could this not happen again in a smaller region of space? $\endgroup$
    – Kronimiciad
    Commented Aug 18, 2016 at 21:14
  • $\begingroup$ You’re mixing things up. Contents of the universe + gravity potential energy are conjectured to cancel out to zero. I was referring to dark energy (not dark matter) as being created as space expands. Within our universe, usable energy does not spontainiously appear; on the contrary it is concerved. Try reading books from Laurence Krause and Brian Greene for more about the universe itself popping into existence. $\endgroup$
    – JDługosz
    Commented Aug 18, 2016 at 21:26
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    $\begingroup$ This is the best text I have ever read on the subject. From now on I'll quote your answer whenever people ask me about this. $\endgroup$
    – The Square-Cube Law
    Commented Aug 19, 2016 at 1:38
  • $\begingroup$ Apologies for mixing the terms up. I will add those books to my to-read list, but it will be a little while before I have the chance. For now, is there a way to explain, in less space than a book, how the universe spontaneously appeared while still conserving energy, and why this process cannot happen again? $\endgroup$
    – Kronimiciad
    Commented Aug 19, 2016 at 1:41
  • $\begingroup$ That might be a good question for Physics, exactly as you have it in the previous comment! If you do, be sure to note a link here so we can follow it. $\endgroup$
    – JDługosz
    Commented Aug 19, 2016 at 2:41
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Short answer no. Zero point energy is basically equivalent to a system having no energy; since the energy of the system can't decrease beyond this point you can't remove any energy from it. Most authorities consider it pseudoscience; the idea of infinite energy doesn't actually make sense in physical terms.

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They can't. Nobody can use zero point energy, it's not a real thing, it's from Stargate. Vacuum energy is real but can't be used for anything either. It's the lowest energy of a quantum state. It's not something you can use to power a car with.

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