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There are a couple of details that make the early universe different then a black hole. The first is that, even though the matter/energy density was higher th
by opwieurposiu 6y ago
There are a couple of details that make the early universe different then a black hole. The first is that, even though the matter/energy density was higher then the Chandrasekhar limit, space itself was expanding at faster than the speed of light so it could not collapse.
The second thing is that gravity has negative energy, and matter has positive energy, so the total energy of the universe was exactly zero. Zero total energy is the only amount compatible with our understanding of thermodynamics.
- politician 6y agoSince gravity is an illusion, did you mean to say that time dilation has negative energy? What does that mean?
- opwieurposiu 6y agoIf you have two apples floating in space, it takes positive energy to pull them apart against the force of gravity. Since energy must balance out, this means the gravitational field has negative energy. https://www.livescience.com/33129-total-energy-universe-zero.html https://www.livescience.com/33129-total-energy-universe-zero... For energy balance it does not make a difference if you think of gravity as a real force or an illusion caused by curved space.
- cygx 6y agoIf you have a positive and a negative charge floating in space, it takes positive energy to pull them apart against the force of electromagnetism. And yet, the energy density of the electromagnetic field is strictly positive.
- politician 6y agoThanks for the explanation.
- simonh 6y agoThere is energy in the curvature of spacetime, in the form of the gravitational stress-energy tensor.
- AnimalMuppet 6y agoOK, but what about before that? Space itself was expanding faster than the speed of light? There had to be a time when that was not true, because as you go back earlier in time, if that continued back far enough it would mean the diameter of the universe was negative. That's clearly absurd. But that leaves you with all this mass, inside the Chandrasekhar limit, but the universe not expanding faster than the speed of light. And then it starts expanding. All this presumes that time can be thought of as extending back before the big bang, which I don't know if that's actually a valid idea. I have heard the claim that the laws of general relativity allow for a white hole as well - a singularity from which things go out, instead of things going in. That may be an accurate picture, or at least a decent model.
- opwieurposiu 6y agoThe big bang theory gets weirder the further back you go. I agree with you that at a certain point it starts to seem pretty hand-wavy. A popular explanation is that at very high energies, the laws of physics work differently, IE gravity, strong, weak and electromagnetic force were all combined into one and there was negative mass. https://en.wikipedia.org/wiki/Chronology_of_the_universe#Planck_epoch https://en.wikipedia.org/wiki/Chronology_of_the_universe#Pla...
- vl 6y ago>OK, but what about before that? Well, the standard answer is that “time didn’t exist”. This is of course in unsatisfactory. The truth is that nobody knows, and so far it looks like we are unlikely to know. If you think about it, it doesn’t make much sense at all: some huge amount of matter, came from somewhere, space expanded with it. Why? Where it came from? What is the reason? This is the area, where scientists that dwell on it too much, start to go crazy or become overly religious.
- andrewflnr 6y ago> gravity has negative energy Pretty sure that's wrong. Citation needed.
- cygx 6y agoYou can apply Noether's 2nd theorem to Friedmann cosmology with cosmological time as your generator. This yields the expected contributions to the energy density, with an additional negative term that is (if I remember correctly) proportional to H² and gets interpreted as energy of the gravitational field by some.