There’s no such thing as absolute speed in the universe. But there is relative speed. That’s how fast something is going, from something else’s point of view. The speedometer on your car measures your speed relative to the road. But another car on the road next to you would say your speed is 0, because from their point of view you aren’t moving. That is to say, you’re going the same speed.
We used to think relative speeds just added or subtracted together normally. The same rules you learned in math class. But Einstein figured out that isn’t true. See, Einstein and many others knew that the relative speed of light is always the same. No matter how fast you’re going, light is faster. And always by the same amount. You can never get closer to the speed of light. It didn’t make sense to anyone until Einstein figured it out.
Einstein realised that the faster you’re going, the slower time passes. So even if you’re going at a million miles an hour, you just slow down, and now from your fast/slow point of view, light is still beating your speed by the same amount. You don’t experience time as slower, but anyone looking at you would see you moving in slow motion.
That’s how drag’s high school physics teacher explained it to drag. Drag oversimplified a bit, but all the important bits are there, and anyone could figure out the rest if they spent the time thinking about it. Anyone who thinks relativity is hard to explain doesn’t understand it. That’s what Einstein was saying.
That’s special relativity. General relativity is the theory of the curvature of spacetime as the mechanism for gravity. Large masses curve spacetime more than small masses. Under GR, gravity is not a force.
Good point but why “no bowling ball on a trampoline nonsense”? That’s not a correct analogy, since it deforms “space” different from how gravity transforms space, but it’s good enough to understand how that works, I think
Oh because that incorrect analogy is the most common “lay person” analogy for describing gravitational curvature of spacetime. The most common reply from children is that it’s the earth’s gravity pulling down on the bowling ball so that the trampoline demonstration wouldn’t work in space.
Also the trampoline analogy doesn’t show us how gravitational lensing works, nor does it even touch how different gravitational reference frames affect the passage of time (GR generalizes special relativity, after all).
Affecting passage of time looks like a difficult idea to come up with an analogy.
For the better gravity analogy, I think a rubber sheet that has something pulling together at a “gravity well” and lines drawn on it may work better, but I’m not sure 😅
The harder thing to convey is the full dimensionality of it. With the rubber sheet (or trampoline) you can show a small ball orbiting around a larger one but only in a single plane (around the “equator” of the large ball). However in reality you can orbit in any direction you like and many satellites actually orbit over the poles. Trying to show that with a small model seems extremely difficult!
Furthermore, most children are raised on the idea that gravity is pulling them down. They intuitively understand the idea that when they climb a ladder and drop a ball from the top, the earth pulls the ball down. General relativity tells us that this is not happening at all! That there us nothing pulling us down whatsoever. I have yet to see anyone provide a lay person GR explanation for the ladder problem.
There’s no such thing as absolute speed in the universe. But there is relative speed. That’s how fast something is going, from something else’s point of view. The speedometer on your car measures your speed relative to the road. But another car on the road next to you would say your speed is 0, because from their point of view you aren’t moving. That is to say, you’re going the same speed.
We used to think relative speeds just added or subtracted together normally. The same rules you learned in math class. But Einstein figured out that isn’t true. See, Einstein and many others knew that the relative speed of light is always the same. No matter how fast you’re going, light is faster. And always by the same amount. You can never get closer to the speed of light. It didn’t make sense to anyone until Einstein figured it out.
Einstein realised that the faster you’re going, the slower time passes. So even if you’re going at a million miles an hour, you just slow down, and now from your fast/slow point of view, light is still beating your speed by the same amount. You don’t experience time as slower, but anyone looking at you would see you moving in slow motion.
That’s how drag’s high school physics teacher explained it to drag. Drag oversimplified a bit, but all the important bits are there, and anyone could figure out the rest if they spent the time thinking about it. Anyone who thinks relativity is hard to explain doesn’t understand it. That’s what Einstein was saying.
That’s special relativity. General relativity is the theory of the curvature of spacetime as the mechanism for gravity. Large masses curve spacetime more than small masses. Under GR, gravity is not a force.
Good point but why “no bowling ball on a trampoline nonsense”? That’s not a correct analogy, since it deforms “space” different from how gravity transforms space, but it’s good enough to understand how that works, I think
Oh because that incorrect analogy is the most common “lay person” analogy for describing gravitational curvature of spacetime. The most common reply from children is that it’s the earth’s gravity pulling down on the bowling ball so that the trampoline demonstration wouldn’t work in space.
Also the trampoline analogy doesn’t show us how gravitational lensing works, nor does it even touch how different gravitational reference frames affect the passage of time (GR generalizes special relativity, after all).
Affecting passage of time looks like a difficult idea to come up with an analogy.
For the better gravity analogy, I think a rubber sheet that has something pulling together at a “gravity well” and lines drawn on it may work better, but I’m not sure 😅
The harder thing to convey is the full dimensionality of it. With the rubber sheet (or trampoline) you can show a small ball orbiting around a larger one but only in a single plane (around the “equator” of the large ball). However in reality you can orbit in any direction you like and many satellites actually orbit over the poles. Trying to show that with a small model seems extremely difficult!
Furthermore, most children are raised on the idea that gravity is pulling them down. They intuitively understand the idea that when they climb a ladder and drop a ball from the top, the earth pulls the ball down. General relativity tells us that this is not happening at all! That there us nothing pulling us down whatsoever. I have yet to see anyone provide a lay person GR explanation for the ladder problem.
Not in Australia, though