Marching On

One of the things noted in stories about last week's death of physicist Stephen Hawking was that his work had a lot to do with trying to find theories that could reconcile gravity with quantum theory. An experiment proposed by three physicists in two recent papers could pave the way for that to happen.

"Quantum theory" is called that because it supposes things we see as flowing forces are actually discrete particles if you look closely enough. To the naked eye a stream is flowing water, but it is actually made up of water molecules that are so small our eyesight can't pick them out. Matter may seem like it is solid, but we know it is made up of tiny atoms, and between those atoms is open space. It's just that on the scale of everyday life and existence, the atoms are so small that they appear to be a single object.

Three of the four basic forces of the universe -- electromagnetism, the weak nuclear force and the strong nuclear force -- have been demonstrated to be, at their most basic level, quantized. At that level they are not smoothly flowing forces but instead are individual particles, smaller than atoms themselves.

Gravity has resisted joining the group. Its particles have been theorized and named gravitons, but neither they nor any proof of their existence has ever been found. Part of the problem is that gravity is very very weak compared to the other forces, which means that the effects of its quantum nature are very hard to detect. Put a hand into a stream of moving marbles, for example, and it will not be tough to feel the effects of the individual marbles that make up the stream. But put it into that earlier-mentioned stream of water and there will be no sensation at all of the individual particles, just the force of them all flowing together in the same direction making up the current.

One of the interesting things about the experiment proposed in the two scientific papers is that if it is successful, it will still not detect gravitons. It will only show whether or not certain effects happen as if there were gravitons and gravity is also a quantum phenomenon. If the experiment works like the scientists hope, then their results will be the same results as they would get if gravity is quantized. It will still leave the question open and leave scientists hunting for those particles -- and nagged by the possibility that other things might have caused the experiment to turn out that way. Sure those things would be weird and unexpected and not at all what anyone would have seen coming.

But the universe has been known to do that, so the hunt will continue.