"most accepted theory of physics is that the universe started from a single point": This is not true. The most accepted theory is that the universe was extremely dense, but it is not accepted that it was literally a "point" of zero volume. Our laws of physics are thought to break down beyond a certain density of matter, so we don't have any reliable predictions about it. The "dense" universe could still have been infinite even back then. Just super dense and infinite in all directions - and now all of it has expanded and it's still infinite (a bigger infinity?).
adrian_b|2 years ago
The properties of the observable universe are consistent with an initial state where the temperature was so high that the protons and neutrons were free, not bound in atomic nuclei, like today.
This means that the temperature corresponded to a kinetic energy of several tens of MeV per particle. At such a temperature, the state of the matter is a plasma composed only of protons, neutrons, electrons, positrons, photons and neutrinos.
At this temperature, the matter has the simplest possible composition. At lower temperatures the particles become bound in nuclei, atoms and molecules, which become more and more complex with decreasing temperatures. At increasing temperatures, the higher the temperature is, more and more mesons, baryons and heavy leptons are generated and the plasma composition becomes more and more complex.
However, at that temperature where the matter has the simplest composition, any traces of its former evolution have been practically erased and we do not have any rational reason for making suppositions about it. Perhaps the matter was indeed even denser and even hotter, but there is no basis for this extrapolation except some philosophical belief that is not based on any scientific observation.
An extrapolation towards greater temperatures and densities could be justified only if we knew boundary conditions around the universe, which we do not know.
In conclusion, what can be known with reasonable certainty about the Big Bang starts from a moment in time when the temperature corresponded to a kinetic energy of several tens of MeV per particle, and all extrapolations to times before that moment are hypotheses that are not based on any experimental data, so they can be neither verified nor falsified.
The supposition that the Universe may have started from a single point is something that has nothing to do with science, but it may be a valid religious belief.
sillysaurusx|2 years ago
ben_w|2 years ago
aziaziazi|2 years ago
- today’s observable universe is roughly 13.8B years. By the time you travel to the edge of that universe, others stuff has travel from that edge to even further position at various speed including faster than you do. Therefore you never get to that edge, making it infinite.
- before/at big bang universe is a single point. You are within this single point but can’t go outside because time does not exist and traveling need time.
- when the big band happened, it grew in size very, very fast, close to speed of light. During that enlargement phase it grew to the size of an Apple and if you were within it and try to look in any direction, the further think you can see is the Apple skin. That’s the observable universe. But to see the skin you need to go there or wait for particule to come to you (eg photon). By that time the universe has already dilated and grown a lot wider. Some particules from the skin are already far away. You’ll never be able to see them : by the time needed for information to come to you, other information goes in the opposite direction.