Cosmologic philosophy: getting something from nothing? (Introduction)

by David Turell , Wednesday, July 24, 2019, 18:11 (1949 days ago) @ David Turell

Ethan Siegel tries to answer about this universe. Guth in his book " The Inflationary Universe" tells us the energy in the universe adds up to zero; Siegel disagrees:

https://www.forbes.com/sites/startswithabang/2019/07/20/ask-ethan-can-we-really-get-a-u...

"You very likely think about nothingness as a philosopher would: the complete absence of everything. Zero matter, zero energy, an absolutely zero value for all the quantum fields in the Universe, etc. You think of space that's completely flat, with nothing around to cause its curvature anywhere.

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"If we want to think about nothing in a physical sense, you have to keep certain things. You need spacetime and the laws of physics, for example; you cannot have a Universe without them.

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"But here's the kicker: if you have spacetime and the laws of physics, then by definition you have quantum fields permeating the Universe everywhere you go. You have a fundamental "jitter" to the energy inherent to space, due to the quantum nature of the Universe. (And the Heisenberg uncertainty principle, which is unavoidable.)

"Put these ingredients together — because you can't have a physically sensible "nothing" without them — and you'll find that space itself doesn't have zero energy inherent to it, but energy with a finite, non-zero value. Just as there's a finite zero-point energy (that's greater than zero) for an electron bound to an atom, the same is true for space itself. Empty space, even with zero curvature, even devoid of particles and external fields, still has a finite energy density to it.

"From the perspective of quantum field theory, this is conceptualized as the zero-point energy of the quantum vacuum: the lowest-energy state of empty space. In the framework of General Relativity, however, it appears in a different sense: as the value of a cosmological constant, which itself is the energy of empty space, independent of curvature or any other form of energy density.

"Although we do not know how to calculate the value of this energy density from first principles, we can calculate the effects it has on the expanding Universe. As your Universe expands, every form of energy that exists within it contributes to not only how your Universe expands, but how that expansion rate changes over time. From multiple independent lines of evidence — including the Universe's large-scale structure, the cosmic microwave background, and distant supernovae — we have been able to determine how much energy is inherent to space itself.

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"All we can say is that when we measure the expansion rate of the Universe, our observations are consistent with dark energy being a cosmological constant with a specific magnitude, and not with any of the alternatives that evolve significantly over cosmic time.

"Because dark energy causes distant galaxies to appear to recede from one another more and more quickly as time goes on — since the space between those galaxies is expanding — it's often called negative gravity. This is not only highly informal, but incorrect. Gravity is only positive, never negative. But even positive gravity, as we saw earlier, can have effects that look very much like negative repulsion.

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"... because dark energy is a property of space itself, when the Universe expands, the dark energy density must remain constant. As time goes on, galaxies that are gravitationally bound will merge together into groups and clusters, while the unbound groups and clusters will accelerate away from one another. That's the ultimate fate of the Universe if dark energy is real.

"So why do we say we have a Universe that came from nothing? Because the value of dark energy may have been much higher in the distant past: before the hot Big Bang. A Universe with a very large amount of dark energy in it will behave identically to a Universe undergoing cosmic inflation. In order for inflation to end, that energy has to get converted into matter and radiation. The evidence strongly points to that happening some 13.8 billion years ago. (m y bo ld)

"When it did, though, a small amount of dark energy remained behind. Why? Because the zero-point energy of the quantum fields in our Universe isn't zero, but a finite, greater-than-zero value. Our intuition may not be reliable when we consider the physical concepts of nothing and negative/positive gravity, but that's why we have science. When we do it right, we wind up with physical theories that accurately describe the Universe we measure and observe."

Comment: The energy in this universe is not nothing. It was created from some sort of energy which existed prior to the Big Bang. It implies a creator. I've omitted his long discussion of the meaning of gravity in this issue for the sake of brevity.