MICHELLE THALLER: So Jemima, you ask a really interesting question, do the tides affect the water in our body? Now the simple answer is no, but let's talk about why that's true. The tides are caused every day by the moon and the sun stretching the earth, the gravity actually stretches the earth apart just a little bit. Now the earth is a very large object, but think about smaller things now. Do you ever notice tides on a lake? For a very large lake like the Great Lakes there might be a little bit of a tidal difference every day, but it's actually kind of hard to measure. What about a smaller lake or a pond? What about something like a swimming pool?
I think even in your own experience you can see that smaller objects don't really have any tidal differences across the day and that's just because of the size. As we said the tides are caused by the gravity of the moon and the sun stretching the earth, but now take it down to a really, really tiny scale. Over really small scales there just isn't much of an effect, you really can't sense it at all it just becomes unimportant.
Now the interesting thing is that this would not be the case if we were around something like a black hole. If you were around a black hole, which is a dead star, and say the mass of the black hole was about 20 times the mass of the sun, a black hole like that is actually not very physically large you have all that mass but the black hole itself may only be say on the order of 30 miles across. That means you have all that mass packed into a tiny little area. If you were nearby a black hole that means there really would be a detectable gravity stretching across something as small as your body and not just the water in your body would feel that. As you got closer and closer to a black hole you would actually feel your head stretched away from your feet. There would be tidal forces, just like the earth goes through with the sun and the moon, but next to a black hole the gravity is so extreme there would be tides over something as small as a human body. Get closer and closer to a black hole and your head keeps getting stretch more and your feet keep getting stretched that way and you would actually turn you into a stream of particles.
Scientists have a really cool name for this it's called spaghettification from the word of spaghetti. If you got close to a black hole there would be tides over your body that small that would rip you apart into basically a strand of spaghetti that would fall down the black hole.