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Mon Mar 7, 2016, 12:01 PM

Death by gamma-ray bursts may place first lower bound on the cosmological constant

From phys.org:


The number of protective halos increases as the value of the cosmological constant increases (different colors of lines represents different values of the constant). The two graphs represent two different sizes of halos, though they give similar results: for example, both show that few halos existed more than 7 billion years ago, which fits with the age of the Earth being about 4.5 billion years old. Credit: Piran, et al. ©2016 American Physical Society
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Clearly, the farther away a planet is from gamma-ray bursts, the better its chances of harboring advanced forms of life. In a new paper, scientists have shown that the gamma-ray burst risk to life favors a universe where all objects (like planets and gamma-ray bursts) are relatively far apart. And the main factor that tells how far apart everything is in the universe—or in other words, how things are spreading out and moving away from each other—is dark energy or the cosmological constant.

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Currently, the value of the cosmological constant is estimated to be about 10[sup]-123[/sup]. Researchers have placed upper bounds on this value (it can't be more than 10[sup]-120[/sup] or else galaxies and other structures could not form because their matter could not have gotten close enough together). But so far, no research has been able to place a lower bound on the value.

By showing that the chances of advanced life existing is extremely small when planets are close to gamma-ray bursts, the new study makes an argument for placing the first lower bounds on the value of the cosmological constant. The scientists estimate that, when the value gets below 10[sup]-124[/sup], the number of protective "halos" of space (regions where planets stand a chance of avoiding gamma-ray bursts for long periods of time) sharply decreases. In other words, it would be pretty unlikely for humans to exist if the value were smaller than this number.

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Reply Death by gamma-ray bursts may place first lower bound on the cosmological constant (Original post)
Jim__ Mar 2016 OP
Agnosticsherbet Mar 2016 #1
eppur_se_muova Mar 2016 #2

Response to Jim__ (Original post)

Mon Mar 7, 2016, 12:12 PM

1. Great article.

I'll need to read it through at leisure three more time to understand it, but fascinating.

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Response to Jim__ (Original post)

Mon Mar 7, 2016, 01:57 PM

2. Can't base statistical arguments on a single sample.

We exist, no matter how improbably. Doesn't matter what the statistics are -- we don't even know if we're the only case or one of quadrillions.

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