One of the fundamental questions of mankind is what is the fate of the universe. Hopefully its a long way off. Astronomy has always factored into cosmology and it shouldn’t be any surprise that many of NASA’s probes have studied the factors that may determine our long term outcome. Working with ground based observatories and scientists around the world, recent information has been startling.
First you have to understand that the universe is expanding. Edwin Hubble, for whom the great orbiting observatory is named, discovered that objects at great distances from us are flying away from us with a speed that increases with their distance. If you can measure their speed — which astronomers due by seeing how much the light from an object is shifted to the red end of the spectrum — you can get an accurate indication of how far away they are. The conversion factor between red shift and distance is called the Hubble constant. Edwin Hubble worked in the early part of the 20th century, this is all old news, where are we headed?
One of the big debates in cosmology is whether or not the universe is open or closed. That is, will it expand forever with the stars getting farther and farther apart until the universe suffers what some have called a freezing death? Or at some point will the universe start contracting, headed back toward that density that existed at the beginning which has been called the big crunch (opposite of the big bang)? Turns out it is almost too close to call from the observations we could make from the ground.
But we started sending probes into space. For example the Hubble (the telescope, not the astronomer) has started measuring red-shift and distance much more precisely than we can on the ground. And we sent two probes to study the background radiation lingering from the Big Bang: COBE and WMAP. And they found . . . .that the speed at which the universe is expanding is . . . (drum roll) . . . accelerating!
How can that be? Shouldn’t gravity be slowing things down? Whew. The theoreticians went to work with the data. Turns out that Einstein had it right, except he thought he was wrong. He had put a constant in one of his equations — the Comological Constant — which he later said was his biggest blunder. Now, it seems it wasn’t a blunder at all. Something is making the universe expand faster as time goes on.
Scientists can’t see it, and they can’t measure it, but the only explanation they have for this phenomenon is dark energy. Dark energy must pervade every cubic inch of the universe but we have never detected it. It must cause this acceleration; that is the only possible explanation, so they say.
Whew. Talk about finding out what you didn’t expect. So the universe won’t end in the big freeze or the big crunch but will start expanding so fast that it will end in a big rip!
I wouldn’t worry any time soon. Likely long after we’re gone and long after the earth is baked to a cinder by a dying sun.
So why do we care? Other than the academic interest, that is?
Could we do something with dark energy? I mean, if we could get hold of it. Might get more miles per gallon than gasoline! We’ve just started to figure this out. Some smart person, knowing that it is there, will figure out how to harness it.