My physics friend suggested that "the answer to why matter exists in the universe" is because all massive particles are just the fabric of space excited into little packets. To illustrate, imagine a blanket on the ground. Then, pinch a small bit of the blanket and twist it. This is a particle that has mass.

It was intriguing to hear this (he's only studied up through Freshman year of college physics), but there are clear flaws (i.e. angular momentum of a "particle" tied to a "blanket"??).

Regardless, it made me wonder about vacuums. Is there any theory that suggests that a vacuum actually has energy in some form or another?

  • $\begingroup$ Somewhat related: physics.stackexchange.com/q/105949 $\endgroup$ – Hasan Aug 13 '16 at 7:12
  • $\begingroup$ Energy is the ability to perform work. What is a vacuum to perform work on? Even if we know nothing about general relativity and quantum field theory, the logical implications of the definitions of energy and vacuum are already pointing to a rather difficult problem to make such a statement in some way consistent. $\endgroup$ – CuriousOne Aug 13 '16 at 7:43
  • $\begingroup$ Is there a such thing as empty space? $\endgroup$ – Bill Alsept Aug 13 '16 at 7:49
  • $\begingroup$ @BillAlsept in the universe? I couldn't say. In theory? Yes, remove all particles and fields. $\endgroup$ – whatwhatwhat Aug 14 '16 at 4:59

Particles are not regarded as bits of curved spacetime, but rather as excitations of quantum fields.

It has been suggested that spacetime curvature can cause structures that behave a bit like objects (though not fundamental particles) and these objects are called geons. However it remains unclear whether these would be stable. It also isn't known what impact quantum gravity effects would have on the formation and stability of geons.

The vacuum has a precise definition in quantum field theory and it has a mean energy of zero by definition. However we can have gravitatinal waves propagating where no matter is present, and there is an energy associated with these gravitational waves. You could regard this as a vacuum having energy, though normally we wouldn't call it a vacuum if gravitational waves are present. This energy is in effect the energy of the spacetime curvature, though this turns out to be a rather elusive quantity.

  • $\begingroup$ "though normally we wouldn't call it a vacuum if gravitational waves are present" - By this logic, even if empty space has energy, we could not call it vacuum because energy is present. $\endgroup$ – kpv Aug 13 '16 at 10:00
  • $\begingroup$ @kpv: well yes. The QFT vacuum has zero (mean) energy by definition. If energy is present it isn't the vacuum state. $\endgroup$ – John Rennie Aug 13 '16 at 10:02
  • $\begingroup$ So does vacuum exist at all anywhere in the universe then? Because of CMB.. $\endgroup$ – kpv Aug 13 '16 at 10:04
  • $\begingroup$ @kpv: quite so, since the CMB is present everywhere there is no such thing as completely empty space. But the CMB has such a low energy density that it can be ignored for most purposes. You'd have to be an awfully zealous physics pedant to object to the phrase empty space on those grounds. $\endgroup$ – John Rennie Aug 13 '16 at 10:10
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    $\begingroup$ "...it has a mean energy of zero by definition." What definition do you mean? The precise one that defines vacuum or the one that defines energy? $\endgroup$ – Ján Lalinský Aug 13 '16 at 15:01

Yes empty space does have energy.When you apply quantum mechanics and special relativity, empty space inevitably has energy. The problem is, way too much energy. It has 120 orders of magnitude more energy than is contained in everything we see!


After looking at the other answers and comments, I understand the question little bit better now. So, will take a shot at it.

The question is about own energy of vacuum/space, not about the energy spread in space from big bang etc. There is a difference between the two.

Just like many other questions, this also needs looking at gravity.

Gravity is curving of space in presence of mass/energy. Right?

If space curves in presence of mass, then mass and space must be interacting in some way. Without interaction, the curving would not be possible.

If space is capable of interacting with mass/energy, it has to have its own properties. Can something have properties without having any energy?

I would think empty space has its own energy. Otherwise gravity won't be there.


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