Does alien life exist?

Last month, The New York Times published an article ...

Posted: Jan 4, 2018 2:27 PM
Updated: Jan 4, 2018 2:27 PM

Last month, The New York Times published an article describing a secret government program investigating reports by military pilots of unidentified flying objects they encountered in the course of their daily duties. The media was awash with stories of flying saucers and extraterrestrial encounters, with scientists downplaying the likelihood of alien visitation and UFO enthusiasts exclaiming their excitement.

While I sit very firmly on the side that believes these reports more likely have an unremarkable and terrestrial explanation, whether alien life exists is a very real and credible scientific question. What is the possibility that life -- and even intelligent life -- exists around a star other than our own? And how can we find out?

In 1961, Frank Drake wrote down what is now called the Drake Equation, which is frequently used to help guide thinking about extraterrestrial life. The equation multiplies a string of probabilities -- such as the fraction of stars with planets, the fractions of planets that are habitable, and the percentage of times intelligent life forms -- to give an estimate of the likelihood that we are not alone in the universe.

When Drake wrote down his equation, very little was known about any of these probabilities. They were all pretty much guesses. However, using the best guesses of the day, he estimated there were 10 planets in the Milky Way galaxy emitting radio waves and thereby detectable in principle by Earth-based radio telescopes.

A lot has changed in the last half-century and we now have a much better understanding of some of these numbers.

So, what do we know for sure?

While the universe is vast, let's restrict our investigation to only our own Milky Way, as other galaxies are very far away and the idea of traveling between them is even more daunting than interstellar travel. So, I'll only talk about our celestial neighbors.

The Milky Way has about a hundred billion stars in it, with some estimates four times larger than that. In 2009, NASA launched the Kepler spacecraft to search for planets around distant stars. What the Kepler mission found was nothing short of astounding. We know that most stars have planets (over 80%). About a quarter of those planetary systems have a planet at a distance from the star that would allow for liquid water. And, of those, 10% to 20% of the time those planets are around the same size as Earth. Combining those numbers, we can estimate with some accuracy that the number of possibly habitable planets in our galaxy is in the neighborhood of 200 million.

While there is some uncertainty in this estimate, it is relatively firm. We are far less certain in our estimation of whether life will be created, if it will survive, and if intelligence will evolve. If these life-related probabilities are high, say above 50%, then life should be extremely common in our galaxy. If those numbers are low, we could be alone.

For all these factors, we only have our own Earth to guide us. And, of course, generalizing from a single instance is not a wise thing to do. However, we are not completely ignorant even with just our single planet to study.

What can Earth tell us?

The Earth is about 4.55 billion years old. However, the early Earth was molten and inimical to life. However, by about 4.4 billion years ago, the Earth cooled enough for water to exist on it. We are not certain exactly when life formed on Earth, but conservative estimates suggest that it was no later than 3.8 billion years ago, with some estimates suggesting the earlier date of 4.29 billion years ago.

No matter the estimate, it is clear that life formed on Earth very soon after the planet cooled enough to have liquid water. This suggests that the formation of life is easy. Were it difficult, one would expect that it would have taken longer. This is not an airtight argument, to be sure. But it is a reasonable one.

Although life formed very early in the life of our planet, multicellular life came much later. It wasn't until oxygen permeated the atmosphere that more complex life could be supported. It was about 540 million years ago that life from which humans evolved came into existence. The fact that it took 3-4 billion years for "our" kind of cells to evolve suggests this process is slow and not at all guaranteed. It requires an abundant supply of a volatile chemical like oxygen to happen at all.

However, we also know that life has survived for about 4 billion years, no matter how many times the universe has tried to snuff it out. The impact 65 million years ago that killed the dinosaurs was a dramatic event in the history of Earth, but it was dwarfed by the Permian extinction 250 million years ago, when 90% of the species on the planet went extinct. Yet life survived. Under Earth-like conditions, life is hardy.

The evolution of intelligence seems to be rarer. Until humans evolved, no other forms of comparable intelligence existed. It is somewhat arbitrary where to draw the line, but our own species, Homo sapiens, came into existence perhaps 200,000 years ago. The earliest species of the genus Homo was Homo habilis and they first evolved around 2 million years ago. By either definition, humanlike intelligence took a long time to appear. Further, if humanity were to go extinct tomorrow, there are no species around that are likely to quickly evolve intelligence. Granted, there are species that are more intelligent than others, but their path to humanlike intelligence is by no means assured. From this, it is possible to provisionally conclude that the evolution of intelligence is rare.

Thus, from what we know and can infer from observation, planets are common, life is probably common and intelligence is rare. We can also conclude that life is hardy on Earth, but Earth may exist in an unusual environment. After all, for life to exist, its host star must be stable and it must not be too close to other stars that could go supernova and bathe the Earth with sterilizing radiation. Indeed, some calculations predict that stars near the center of our galaxy -- a relatively hostile environment -- are not good candidates for life to flourish. Some predictions say that only about 2% of stars exist in benign portions of the galaxy, which means that there are maybe 4 million Earth-like planets in our galaxy.

So, what's the answer? Are we alone in the universe? The honest answer is that we don't know. We know that planets that could support liquid water are common. But we don't know much about the origin of life and the probability that it will evolve as it did on Earth. From what we have seen on Earth, it seems that the creation of life is relatively easy, but the evolution of intelligence is hard. Taken in aggregate, it does seem that extraterrestrial life should exist and there may be planets where our cosmic cousins also look at the sky and dream.

Nobody can tell you for sure what those Navy pilots saw (although I'd bet real money that it was something ordinary). But it's a big universe and it seems that life could very well be common. There may come a day when an alien craft lands on the White House lawn like in the 1950s movie "Earth vs. the Flying Saucers," or, more likely, we hear the first signals in our giant radio telescopes.

Then we would know, once and for all, that we are not alone.

Indiana Coronavirus Cases

Data is updated nightly.

Cases: 728811

Reported Deaths: 13405
CountyCasesDeaths
Marion996911740
Lake53548966
Allen40529675
St. Joseph35596550
Hamilton35536408
Elkhart28470441
Tippecanoe22375218
Vanderburgh22293396
Porter18701307
Johnson17923378
Hendricks17199315
Clark12943191
Madison12612339
Vigo12437246
Monroe11873170
LaPorte11856210
Delaware10667186
Howard9895216
Kosciusko9390117
Hancock8260140
Bartholomew8058155
Warrick7777155
Floyd7653178
Wayne7035199
Grant7032174
Boone6687101
Morgan6557139
Dubois6150117
Marshall6016111
Dearborn580077
Cass5794105
Henry5699103
Noble559883
Jackson501172
Shelby490696
Lawrence4522120
Harrison435072
Gibson434792
DeKalb427185
Clinton427053
Montgomery423688
Whitley395239
Huntington390080
Steuben385557
Miami381166
Knox371890
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Putnam359660
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Jefferson329281
White313554
Daviess296299
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Greene277885
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Scott265653
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Clay259447
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Jennings229849
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Jay193630
Carroll188520
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Franklin167835
Tipton162845
Parke146116
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Pike133734
Pulaski116645
Newton107734
Brown101941
Crawford99514
Benton98514
Martin88615
Warren81815
Switzerland7858
Union71010
Ohio56511
Unassigned0414

Ohio Coronavirus Cases

Data is updated nightly.

Cases: 1082815

Reported Deaths: 19428
CountyCasesDeaths
Franklin1258081400
Cuyahoga1119722115
Hamilton799721205
Montgomery514061014
Summit47145945
Lucas42119788
Butler38338584
Stark32273906
Lorain24997481
Warren24274298
Mahoning21546588
Lake20653369
Clermont19761238
Delaware18512133
Licking16418212
Fairfield16176199
Trumbull16032468
Medina15268264
Greene15063244
Clark13983299
Wood13080189
Portage12839203
Allen11639232
Richland11349199
Miami10670217
Muskingum8803133
Wayne8793211
Columbiana8778229
Pickaway8564121
Marion8523135
Tuscarawas8473244
Erie7888154
Hancock6914127
Ross6846155
Ashtabula6805170
Geauga6686148
Scioto6406101
Belmont5881167
Union570848
Lawrence5549102
Jefferson5525151
Huron5430119
Darke5355123
Sandusky5347120
Seneca5282121
Athens519158
Washington5155109
Auglaize490784
Mercer480385
Shelby469293
Knox4486110
Madison435661
Putnam4278100
Fulton422469
Ashland421789
Defiance419697
Crawford3975107
Brown394157
Logan381676
Preble379598
Clinton372163
Ottawa366679
Highland355062
Williams339275
Champaign331658
Guernsey315653
Jackson312551
Perry294950
Morrow284939
Fayette281950
Hardin270864
Henry268666
Coshocton265257
Holmes2603101
Van Wert243463
Adams237852
Pike237634
Gallia235349
Wyandot231055
Hocking215362
Carroll191547
Paulding172640
Meigs144840
Noble133337
Monroe132042
Morgan108423
Harrison108137
Vinton83115
Unassigned02
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