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Can a particle, like an electronic or photon, leave the universe? If the photon for instance travels out toward the edges of the universe, assuming it is flat, will it encounter an invisible wall, or will it leave the universe?

Qmechanic
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He8
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    the universe is by definition the sum of all that exist, so the photon can't escape the universe as there is no "out-of-the-universe-space". If it existed, then it'd be part of the universe. – Vicky Feb 08 '23 at 23:32
  • Possible duplicates: https://physics.stackexchange.com/q/24017/2451 and links therein. – Qmechanic Feb 09 '23 at 03:04
  • A domain wall is a hypersurface separating a false vacuum and could be thought of as a barrier. Other than that, regardless whether the universe is closed or open there are no barriers or places to "fall off". Particles can't exist where the substrate of reality isn't. – BMF Feb 09 '23 at 03:15

2 Answers2

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To the best of our knowledge the universe does not have a boundary or an edge.

Dale
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  • So then no object can leave the universe because it would have to go an infinite distance? There are no points in space where it is impossible to go past? – He8 Feb 08 '23 at 23:24
  • Correct, to the best of our knowledge – Dale Feb 08 '23 at 23:36
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As another way of looking at it, under the current thinking in quantum field theory, the universe is made up of quantum fields. A quantum particle, like an electron or a quark, is simply an excitation (or a vibration or a wave) of the electromagnetic or the quark field. So it would not be possible for a particle to exist where there is no field.

foolishmuse
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