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Is it theoretically possible that energy will be in space without any matter/antimatter/etc in that space? Is it theoretically possible that space will exist with only energy in it and without anything else in that space?

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    $\begingroup$ Isn't that the case for a photon? $\endgroup$ – Steeven Sep 11 '17 at 14:51
  • $\begingroup$ @Steeven Is a photon a pure energy and nothing else? $\endgroup$ – vasili111 Sep 11 '17 at 15:14
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    $\begingroup$ The word energy is too ill defined for it to be clear what you are asking. Do massless particles count as energy? If so then photons, gluons and gravitons all count, though I wouldn't regard them as energy. $\endgroup$ – John Rennie Sep 11 '17 at 15:19
  • $\begingroup$ @JohnRennie if they are particles but have no mass they anyway are particles and thus are matter. Do I understand it correctly? $\endgroup$ – vasili111 Sep 11 '17 at 15:26
  • $\begingroup$ @vasili111: my point is that the distinction between matter and energy is meaningless. Everything has both particle and wave properties. $\endgroup$ – John Rennie Sep 11 '17 at 15:29
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I see there's already an accepted answer, but I wanted to contribute a simpler explanation, since it sounds like that's what you're going for.

In basic mechanical physics, you're probably used to the idea of mechanical energy. When you pull a roller coaster up to the crest of the hill, you've imparted potential energy to it, which it then turns into kinetic energy as it rolls down the hill and through the ride.

But that is only one form of energy. The radio waves that you pick up on your FM radio also have energy. Unlike waves moving through water, these radio waves can travel through empty space and do not require matter to transmit them. Radio waves, light, and other forms of radiation all have energy, but do not need matter.

So yes, you absolutely can have energy without matter, in empty space.

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Yes. Matter is defined by the Pauli Exclusion Principle, which states (oversimplified, thank you minutephysics) that two particles of matter cannot exist in the same quantum state. This principle applies to quarks (which make up, inter alia, protons and neutrons) and leptons (i.e. electrons and neutrinos). However, there are other particles (bosons) which do not follow the Pauli Exclusion Principle and therefore are not matter, but still contain energy. There is no reason that these non-matter particles cannot exist without matter particles existing.

In fact, in the early universe, the energy in space was dense enough to create matter-antimatter pairs from the pure light that was in the universe. For some yet-to-be understood reason, this symmetry was broken and we ended up with more matter than antimatter, which is why there is still matter in the universe. Had this symmetry not been broken, there would be no matter in the universe and only light (which has energy).

Credit hardcore to Henry of minutephysics.

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  • $\begingroup$ You defined matter as the fields that obey the Pauli exclusion principle. I think this is too restrictive. Pions are scalar fields that do not obey the exclusion principle, and yet they are particles of matter (even if they aren't fundamental particles). Also, the Higgs scalar field is counted as "matter". Dark matter may also be made of scalar fields. "Matter" is a general term that has meaning only at a macroscopic level. Is an electron really made of "matter" ? $\endgroup$ – Cham Sep 11 '17 at 16:13
  • $\begingroup$ I would add that "matter" is related to "inertia" and "mass". Every free field/particle that has a "mass" term in its equation of motion should be considered as "matter", while every field/particle that hasn't such a mass term isn't matter and could be considered as "pure energy in motion" (i.e. kinetic energy without mass). $\endgroup$ – Cham Sep 11 '17 at 16:40
  • $\begingroup$ So the W and Z particles aren't matter? Even though they have a rest mass? $\endgroup$ – John Rennie Sep 11 '17 at 17:12

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