What is gravity? Have you ever really thought about it?
In November, I wrote the first of my entries on great academic Albert Einstein. I promised a second part, and here it is – a look at the strange consequences of the general theory of relativity.
Einstein reportedly got the inspiration for his general theory of relativity by imagining what it would be like to release a ball while falling off the side of a building. The person who released the ball wouldn’t see the ball drop, but would see the ball right next to him or her as they both fell (similar to how a feather and a bowling ball fall together when there's no air in the room). Einstein concluded that because gravity affects everything the same way, it must be a result of something happening in space-time which doesn’t depend on the objects it’s affecting.
So quite basically, the general theory of relativity holds that gravity – which seems to be a force pulling us toward the earth according to our weight – is actually a result of the curvature of space-time. Put another way, if an asteroid appears to be pulled towards the earth, it’s actually because of the way space-time is curved around earth, and not because of some force that the earth is extending into space.
There are some mind-bending results from this. One of these is gravitational time dilation, or the phenomenon that time is slower for objects in stronger gravitational fields – if you’re in a place where gravity is strong (on a very large planet, for example), time moves more slowly for you than it would if you were out in space. At the edge of a black hole – where gravity is so dense that it has nothing escapes dropping into the pit that’s been made – time stops. This is why, if you were to watch something fall into a black hole, that object would appear to freeze at the black hole’s edge. You would never see it fall inside.
What happens to the object once inside a black hole? Who knows? The mathematical equation used to calculate these events comes up with an imaginary number in this situation, and no one knows how to represent this imaginary number in real life.
Black holes offered researchers evidence of another effect of general relativity: frame dragging, or the twisting of space-time by a rotating object. Einstein predicted that an object near a rotating body would get pulled out of shape 80 years before the effect was actually observed – the effect is so subtle that science wasn’t able to see it directly at the time. But Einstein’s prediction would show itself in reality by the end of the century.
Many more effects have their theoretical underpinnings in general relativity. Do some of your own research on the subject and you’ll be occupied for as long as you’re interested. And if you're really interested, you can devote your career to studying the physics that Einstein dealt with.
If you’d prefer to have this complex physics explained to you by British cartoon men, view the latter part of this video from Ted Ed. The video also points beyond where Einstein has left us, to a future physics explained by quantum mechanics.