Energy question..

I know we can not go back to the "start" of the big bang but i do have a question about it.

If the universe came from an unknown source of energy then would it make sense to
think that at the beginning is was incredibly small but contained large amounts of energy.

And the reason it could contain large amounts of energy before phase transition into matter is because energy is not a tangible "something" ?

So therefore, energy does not actually take up any space and this is why there can be
so much energy in a very small space ?

Others will have far better answers than I do, but if there was a big bang start as you put it, there was before the start no meaning to space or the size of space so there is no meaning to "incredibly small" since that implies a something in the nothing. Energy, as we know it, is a property we can associate with matter or emanating from matter (radiation) so the possible energy before the big bang is , you might say, speculative.

Where the universe came from is pure speculation, but you're correct that in the early stages the energy wasn't in the form of matter, and thus could be compressed a lot more to give you the high energy density at the beginning. I think that most (all) of it was contained in the postulated inflaton field before it gave rise to matter and radiation by a phase transition triggering the inflation period.

scopeman wrote:

Where the universe came from is pure speculation, but you're correct that in the early stages the energy wasn't in the form of matter, and thus could be compressed a lot more to give you the high energy density at the beginning. I think that most (all) of it was contained in the postulated inflaton field before it gave rise to matter and radiation by a phase transition triggering the inflation period.

I know the beginning is speculative but i am just trying to get an understanding of energy here. So I am right in thinking that there can be an
extremely high energy density in an extremely small space because energy does not take up any space per se.

starfire82 wrote:

scopeman wrote:

Where the universe came from is pure speculation, but you're correct that in the early stages the energy wasn't in the form of matter, and thus could be compressed a lot more to give you the high energy density at the beginning. I think that most (all) of it was contained in the postulated inflaton field before it gave rise to matter and radiation by a phase transition triggering the inflation period.

I know the beginning is speculative but i am just trying to get an understanding of energy here. So I am right in thinking that there can be an
extremely high energy density in an extremely small space because energy does not take up any space per se.

Energy per se does not take up (extended) space indeed.

It may be relevant that fermions (matter) are subject to the Pauli exclusion principle and so matter has volume (see also degeneracy pressure). But bosons, well, don't.

Yes, I think that's an important point-- the basic thing the OP is noting is that matter takes up space but energy doesn't, so we can get very high energy densities as long as there isn't much matter around. It isn't so much matter itself that "takes up space", it is the properties that matter often possesses-- the Pauli exclusion principle (for Fermions, which most of what we would call matter is), and the queer property of matter that it actually requires kinetic energy (lots of kinetic energy) to confine matter into a tiny region. This latter issue is often as important as the Pauli exclusion principle in the reason that matter "takes up space."

It's actually an ironic element of the OP-- the reason solid matter takes up space in the world around us is generally because it does not possess a high enough energy to confine the matter to a smaller volume. The table in front of you is a bunch of matter that would require a huge increase in energy to be compressed into a smaller volume, and that isn't necessarily the PEP, it's just the fact that putting particles into smaller boxes requires giving them energy. It's quite counterintuitive, because we know that giving the particles energy would actually make the table explode, but that's just saying that a table is the special balance where the particles have enough energy to be confined but not too much energy that overcome the forces that are confining them.

Put differently, it isn't energy that confines a table, that's the forces between opposite charges, but it is still true that energy is required to confine things, and what we mean by a "solid" is basically a substance that is somewhere close to maximally compressed, given the energy present (and the Pauli exclusion principle makes it take up a bit more space than a solid would otherwise). So the reason that solid everyday matter takes up space is that it seeks out the appropriate balance between the forces that would pull it together and the energetic requirements for being pulled together. In the case of the Big Bang, you don't have solids, and you don't have degenerate matter, you have ideal gases-- so the matter is invariably far less compact than the energy it possesses would potentially allow. So Big-Bang matter is actually relatively uncompressed, when considered relative to what the energy present might otherwise allow if the matter had a different history.