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7

the two paradigmatic cases that illustrate these two possibilities is a gas, for the first, and a crystal for the second. Paradigms and examples are well and good, but be careful not to assume they are the only possibilities. In particular, black holes have entropy -- a lot of entropy. In fact they saturate the Beckenstein Bound. The entropy of a black ...


3

What I will state is speculative and based on the statistical mechanics derivation of entropy, and just the way I view it and do not consider that there exists a problem. After all thermodynamic theory emerges from the underlying statistical level of atomic and molecular interactions. where p_i is the probabability of microstate i. Setting aside quantum ...


1

"High" and "low" are relative terms that usually also carry an anthropocentric connotation. What "high" means depends on what humans think of as a large quantity but to thermodynamics the absolute scale does not matter! What matters is only that there is a change from one entropic state to another. As long as there is such a change, no matter how slow, there ...


1

In the early Universe, entropy is preserved (dS=0). This comes out of the equations of general relativity, but it can be also understood by thinking in terms of classical dynamics: the Universe is a closed system, no heat is exchanged when expanding, so its entropy must not variate.


13

The low-entropy initial state of the universe is an open problem without a satisfactory answer. Your question is the first time I've heard the suggestion that the initial state should have been a crystal; you remind me that the quark-gluon plasma, which was the state of the universe while it was too hot for nucleons to be stable, has been shown to be a ...


0

The Big Bang is not thought to be an "explosion", but an "expansion" that included "inflation", analogous to dots on the surface of a balloon, that get further apart as the balloon expands. No dot on the balloon is considered to be the central dot, all dots move away from each other. The universe is considered infinite, and consequently, so it was for the


1

Firstly, it is important to note that the old Big Bang cosmology is no longer the most widely accepted theory. We include inflation into the mix in current theories. That said, there is an ambiguity in the definition of the Big Bang (you can find information on that in my question here). If we take the definition of the Big Bang as coming before inflation, ...


0

Does this mean that matter/antimatter (say, an electron and a positron) may be created and annihilate each other, This is called vacuum fluctuations as stated by Quantum Field Theory. In this case energy has to be supplied so that the electron positron pair out of the vacuum would materialize. This does happen at laboratory energies in experiments with ...


1

You don't need oxygen to make an explosion. All that is needed is that the reagents after the explosion occupy more space than those before. Going from solid to gas is a good way of getting this effect. Similarly, going from gas to solid is a good way of producing an implosion, but there is a limit on how much bang you can get from this.


5

The CMB (cosmic microwave background) is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows tiny temperature fluctuations that correspond to regions of slightly different densities, representing the seeds of all future structure: the stars and galaxies of today. The anisotropies ...


1

The CMB is a snapshot of the state of the universe at the moment when the universe cooled enough to allow protons to capture electrons to form atoms, thereby allowing light to travel unimpeded for the first time - prior to this the universe was a remarkably uniform distribution of plasma. But there -were- minute variations, which appear to be a Gaussian ...


0

There were no "pre big bang" conditions. Not physically and not even theoretically. Time itself started with the big bang. How can there be a "time" before the start of time itself?


-1

There is a very simple answer to your question, OP. Big Bang was not only the physical beginning of our universe (the stars, planets, gas clouds, black holes etc) but also the temporal beginning of our universe. That is, there was no "time" before big bang. Time, space and all matter/energy started with the big bang. It might appear funny to think that time ...


1

The Big Bang was not like a black hole. See the canonical question Did the Big Bang happen at a point? to see why. The evolution of the universe from the Big Bang onwards is determined by the FLRW metric and the initial conditions. The FLRW metric is given to us by Einstein's equation, but we have no theory to explain why the initial conditions were what ...


0

If the Universe is infinite, then it had instantly grew from zero to infinity at the moment of Big Bang. Note, that this is a possible model from General Relativity (GR). But most probably GR is not applicable at the moment of Big Bang, because it contains singularity.


0

I think there is no more "slow" light from the begining od the universe remaining because photon has accelerated after expansion to reach their current speed. Maybe I'm wrong but to me it seems to be the right way to think.


4

Your idea that a quantum fluctuation created the universe is a misinterpretation of the suggestions that I have heard. Explaining why requires introducing a few ideas, so bear with me while I do this. The object we think of as the universe is made up of two bits: a manifold equipped with a metric = spacetime some matter/energy The manifold and metric ...


3

There are scientists that do not accept the Big Bang (and more). That doesn't mean that there isn't evidence for the Big Bang (there is), nor does it imply it may be wrong. All we can say is that some scientists consider the Big Bang to be a fact because the evidence is overwhelming, some who think it is the best cosmological model because there is much ...


2

@GeorgeSmyridis: the big bang is a model that describes a bunch of cosmology. Physicists, when referring to it, rarely are talking about the event that happened at the very beginning of the model. In fact, the situation in the model goes outside of the applicable region of known physics before you get to the point in time when the explosion would have ...



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