Time Scales For Humans And The Universe

Only recently, in the scheme of things, have we come to any reasonable understanding of our place in the universe. Only in this century has it become clear that the universe is incredibly old unimaginably immense. We now believe the universe to have evolved from a single point in space at which time, space, matter and energy had no meaning initially. It all got started about 13.6 billion years ago and has now evolved into a space occupied by at least a trillion trillion stars and trillions of galaxies all separated from each other by distances that are hard to comprehend and measure.

We are, of course, on the third planet from the sun, a star formed about 5 billion years ago, at a time when the universe was already nearly nine billion years old. The Earth was created at about the same time as the sun, and after the passage of the nearly 5 billion years, men and women finally appeared. We humans have been here, as near as we can reckon, for about 2.4 million years. Our ancestors came out of the trees, stood upright, made use of primitive tools and fire and now, nearly all of us living today, have evolved almost entirely from a small group that migrated out of Africa some 50,000 to 100,000 years ago. We developed a spoken language sometime thereafter and a written language about 30 centuries B.C. Today, we rule the planet, we think. We have developed this prominence in an exceptionally small span of time when we measure that time in relation to the age of the universe.

We know that many stars have similar lengthy periods of stable life and many of those appear to be surrounded by planets that are capable of harboring life. If life exists elsewhere at all, it could be similar to us or quite different. It is also possible that planets capable of supporting life may have existed in star systems that have now gone extinct. We will never know about that, nor may we ever know about life on planets we can detect orbiting far away stars, as these stars are light years away. Our capabilities are still limited to nearby moons and planets in our own star systems which are are at most light-minutes or light-hours away, not light years. We also have the problem of not really knowing whether there are planets in a potential life-support zone orbiting distant stars or whether the time required for life to develop on those planets has passed. Nevertheless, observing planets orbiting at least nearby stars gives us the good feeling that we may not be alone, even though, so far, we have no evidence about the existence of life anywhere else in the universe. Presumably we have time to find out, but we won’t likely know the answer to that question anytime soon.

We know certainly that life on Earth was tested over time by many hard realities such as the super volcano, ice ages, and large asteroids. Some of these produced massive species die-offs in the past, but life and, indeed, human life always survived. Still, here we are just having completed a century in which we have arguably learned more than we may have learned about the Earth and the universe in all the previous centuries together.

Our species is 2.4 million years old, and given the fact that we are descendent from a relative few who survived to begin the great migration out of Africa 50,000 to 100,000  years ago, most of us would argue that we’re just getting started. We ought to be allowed to continue.

Our star, the sun, is about 5 billion years old. It has a power output that is quite stable, although it has had some recent ups and downs. It releases heat on a reasonably steady scale by an outward pressure from nuclear fusion reactions balanced against the crushing gravitational collapse of it’s predominantly hydrogen-helium core. Its molten outer surface has a complex current which facilitates movement of its enormous energies to the surface and subsequent escape. Energy escape is accompanied by flares that are recognized as sunspots which sometimes vary in number and size but generally occur at high levels or low levels in approximate 11 year cycles. These have been reasonably similar and reproduced in consistent 11 year cycles since the last time they were not–during the low sunspot activity of the sun which occurred during the so-called Maudner Minimum. This low solar output happened at the time of the Little Ice Age. Since then, some believe the sun has fully recovered and is warming us with moderate consistency ever since.

The mass of our sun is consistent with a 10 billion year life span, possibly a little more or a little less. Some consider that the sun may be slowly warming and that may translate into a shorter life span. The shortest prediction is that the sun may begin to burn out its inner hydrogen-helium core at an increased rate and begin to move into it’s red giant phase in as early as 1.4 billion years. A yellow dwarf star (our sun) becomes a red giant when it starts to burn it’s inner helium core and allows it’s residual hydrogen to be burned in its outer shell. The red giant expands in size and begins to burn up it’s inner planets. In our case, Mercury and Venus will be absorbed by the intense heat of the sun’s red shell first, and as this occurs, life on Earth will become unbearably hot, then the oceans will boil away as the planet is consumed.

If the 1.4 billion year estimate is correct, then we will probably only have about one billion years because things may start getting really hot by then. But a billion years is still a very long time. Recall that one billion is a thousand million. That would give human life about a thousand times more that the time it has already had, or equivalently, one million more millennia. If one hundred years of age is the average life expectancy over that time, then that will give us at least one hundred million more generations. Thus, another billion years or even half a billion years, is an incredibly long time compared with what we’ve managed to date.  I’ll take it.

Of course, we have other problems, only some of which we may be smart enough to anticipate. We may have another ice age.  Indeed, as they have been appearing regularly at about 100,000 year intervals, one may be due in 40,000 to 50,000 years or so. We could also be unlucky enough to be on a collision course with radiation released from a distant dying star which produces a highly focused beam of x-rays or gamma rays. Such a beam might catch us directly or hit our sun and accelerate the conversion to a red giant. But given the way things are set up in the universe, we would not see those rays coming until they were on us and then, if they were hot or intense enough, by the time they reached us, it wouldn’t make much difference. On the other hand, their arrival might still give us a few million years or so to decide what to do.


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