Published: 7:04 AM 11/19/2014
Some of our most enduring stories and movies are about first contact...
One of the questions many of us have asked while gazing up at the night sky is: "Are we alone?"
Since the dawn of intelligence on the planet, humanity has pondered this question. Some people have claimed to have had contact with creatures from other planets while others swear up and down that they have seen unidentified flying objects that can't be anything but vehicles from extraterrestrial civilizations.
Popular culture is replete with tales about aliens and some of our most enduring stories and movies are about first contact and battles fought against invading contraterrene armies. Many of us want to believe that it is just a matter of time before alien intelligence is discovered somewhere in the universe.
But, as The Economist notes, life springing by happenstance from random elements combining at just the right time may be nearly impossible.
In a paper recently published on arXiv, Tsvi Piran of the Hebrew University of Jerusalem and Raul Jimenez of the University of Barcelona argue that human beings might just be the first form of intelligent life that has evolved in the Milky Way Galaxy. Piran and Jimenez have studied gamma-ray bursts, which The Economist noted are the most energetic phenomena yet discovered in the universe.
"No one is certain what causes them, but the leading theories are a hypernova -- the sudden collapse of a massive star to form a black hole -- or a collision between two neutron stars, the ultra-dense remnants of supernovas.
What is not in doubt is their prodigious power: a typical GRB generates as much energy in a few seconds as a star will in its entire multi-billion-year lifetime. That would be bad news for any life-bearing planet which was too close."
GRBs occur about once a day (the strongest of which are known as long gamma-ray bursts) all across the universe, noted The Economist, and with all the billions of galaxies out there, that is a reassuringly low rate.
Using the data collected in relation to these daily GRBs, Piran and Jimenez are able to extrapolate the risks posed by gamma-ray bursts to planets. If one was to hit the Earth, noted The Economist, it would basically fry the planet and all life on it.
According to the calculations of Piran and Jimenez, there is a 90 percent chance that Earth has been hit by a gamma-ray burst in its 4.6 billion years, and a 50 percent chance that it's happened in the last 500 million years.
"Any extinction that happened before about 540 million years ago, when shelly animals appeared and fossils became commonplace, would probably be invisible in the geological record," noted The Economist. "But since then there have been five -- one of which, that at the end of the Ordovician period, has no obvious explanation."
If you think this is far-fetched, consider this: In December 2004, a neutron star 50,000 light years away from Earth flared up, sending so much radiation our way that our magnetosphere briefly flickered.
"Although the SGR 1806 -20 flare was relatively mild, it was an unwelcome reminder that life on this planet is constantly threatened by events of unimaginable power," wrote the editors of Physics arXiv Blog.
According to Piran and Jimenez, gamma ray bursts occur more frequently in younger galaxies, indicating that as a galaxy ages, the chances that intelligent life could evolve become greater.
"They reckon that, before about 5 billion years ago, GRBs were so frequent that life would have struggled to establish a foothold anywhere in the cosmos," wrote The Economist. "If astronomers ever do discover life on another planet, then, it is unlikely to be much older than life on Earth itself."
Jaime Green, writing for Astrobites, noted that the gap between origin of life and origin of intelligence is a big one.
"Space is a dangerous place for a little planet, and lots of things can happen to cripple or eradicate its fledgling life. (Piran and Jimenez) find that the innermost 25 percent of Milky Way stars are likely to see lethal LGRB events at least once per billion years. A billion years into life on Earth, we had just barely mastered photosynthesis and were still a billion years away from cell nuclei. Imagine if every time we got there, the slate was wiped clean by a GRB. We wouldn't manage to get very far."
Other portions of the universe, where galaxies are more densely packed than in the Milky Way's neighborhood, may not be so friendly to life due to the frequency of gamma-ray bursts.
"Earth-like is not so simple, nor is the habitable, or 'Goldilocks' zone," noted Green. "And now we see that the habitable zone is not just a a planet's orbit around its star but a star system's place in its galaxy and the universe."
Brain Cox, an English physicist and host of "Wonders of the Universe," recently told Vice our place in the universe (and the multiverse, if that theory is true) "is insignificant."
"But, there's also the other thread -- that, from a biological perspective, life might be rare, and intelligent life might be very rare. And these two things are pulling at each other."
Though Cox finds it terrifying that we may be alone in our galaxy, he is also liberated by that same thought.
"If we begin to suspect that we are very, very rare indeed, then we are very, very lucky. So we should start behaving differently. We should look after ourselves better than we do, because right now, we as a species don't have a particularly universal perspective on our own existence. I think we're rather myopic usually."
In other words, life is precious, maybe even more precious than we previously believed. Perhaps it's time we started to act that way.