Far out cosmology: does dark energy kill galaxies? (Introduction)

by David Turell , Thursday, March 23, 2017, 13:48 (2800 days ago) @ David Turell

We may be in an area of dark energy that is different from other regions of the universe, or not:

http://nautil.us/issue/46/balance/can-dark-energy-kill-galaxies?utm_source=Nautilus&...

"We’re not sure what is causing the expansion to accelerate, so we’ve called it “dark energy.” Our best theories of what matter is and does give us a candidate for what dark energy might be—something called vacuum energy. It’s the energy in a region of space, contained in the electromagnetic field and its cousins, even when there are no particles. But when physicists attempted to calculate the amount of vacuum energy, they got a shock. The answer was about 10^120 times larger than the actual value learned from observation. This is a problem.

"Steven Weinberg, the Nobel Prize-winning physicist, had wrestled with the theoretical overestimate and suggested a remarkable solution. He noted that the amount of vacuum energy can vary from place to place, depending on how all the different fields in the universe add and subtract. In our region of space, the amount of vacuum energy is minuscule, requiring all these fields to cancel one another out to an incredible degree. That seems highly improbable, but in any large enough system, even the most improbable event will occur somewhere. In the vast majority of cosmic regions, the excess of dark energy throws off the balance of forces that enables galaxies, stars, planets, and people to form. We see an improbably precise cancellation of known and unknown fields because we couldn’t exist otherwise.

"Our cosmic environment is the result of a delicate balance of cosmic forces—gravity and pressure, cooling and heating, expansion and collapse. The final product, when all these pushes and pulls come into balance, is our Milky Way galaxy, where stars form in a rotating disk of gas and a diffuse halo of dark matter.

***

"With this physics, and weeks to months on thousands of linked computers, these simulations reveal a condensing web of cosmic structure, with dark matter and ordinary matter coming together to produce remarkably realistic galaxies. If Weinberg is right, this process should not work in regions of the universe that have more dark energy.

***

"If we continue to ramp up the dark energy, the formation of structure freezes before even the smallest galaxies form. None of the matter in the universe manages to form into galaxies, stars, planets, or people. The entire universe is stillborn—a diffuse, expanding gas of particles that very occasionally bounce off each other, but do little else. There is no life, because there is no structure or complexity at all.

***

"In our universe, star formation was most efficient a few billion years before dark energy started driving accelerating expansion. By the time galaxies were isolated by cosmic acceleration, star production was declining anyway. Stellar feedback is the major reason why the universe doesn’t form stars very efficiently. Dark energy is only a secondary villain.

***

"Suppose there are other regions of the universe with more or less dark energy than we have. Essentially, each region picks a number between zero and 10^120, on a scale where our own region picked 1. Now imagine taking your survey clipboard around to check on the lifeforms that evolved in those regions; if you meet one, ask how much dark energy they see. Most regions are dead, of course, which explains why there is no one to tell you, “My region picked 10^30 or 10^90.” But there are plenty of observers who see 10 or 100 or more, in which case we might wonder why we are the outliers who see a value of 1. If the theory says “expect about 100,” but we see 1, we cannot explain our value as a mere selection effect."

Comment: Barnes is suggesting we live in a special place in the universe which supports our very special Milky Way. Is this God at work to protect life in a vast universe? Makes sense to me. Read the entire article to follow his reasoning.