3 ms·

But which direction does this pear shaped atom point? Towards the big bang?

gus_massa 10y ago
They usually point in a random (special) direction. If you put the atoms inside a magnetic field they will point to the north pole or the south pole, all of them will point in the same direction, but I'm not sure which one. The idea is that if see a film of the universe with the time in reverse, the laws will be exactly the same. You will notice some global problems, like an egg getting magically rebuild after it is scattered on a wall. But if you look at each particle individually you will not notice anything strange. This is called the T symmetry. https://en.wikipedia.org/wiki/T-symmetry https://en.wikipedia.org/wiki/T-symmetry The problem is that the T symmetry is not a real symmetry. There are some tiny details that are different when you look carefully. This is totally not related to the broken egg problem. Just ignore the eggs. I'm not sure now about the details, but IIRC when you reverse the velocities of all the particles, then the electromagnets have the current flowing in the other direction. But the atom nuclei have a tiny magnetic moment, due to spin, that is not reversed. So [mmm] and then [mmm] so it's obvious that all the atoms nuclei have to be ellipsoids, not have a pear shape. They have to be symmetric in the direction of the spin. They apparently measured (indirectly) the shape of some atom nuclei and they have a pear shape, so it's a new experimental prove that the T symmetry is broken. IIRC all the previous proof were more indirect. If you see the film of the universe in the reverse direction, you can look carefully at this atoms inside an electromagnet and see that the pointy part of the pear is in the wrong direction. (Assuming they hide all the eggs and other objects than can give you an easier clue.) This operation T is called time reversal, and it gives a lot of useful information about systems where the broken part of the symmetry is negligible. In particular if you want to calculate the properties of a small molecule, you can use this property to reduce a lot the amount of calculations. You may be wondering how is this related to Time Travel ... me too. Probably is the linkbait version of Time Reversal, that is a too nice name for a simple operation.

They usually point in a random (special) direction. If you put the atoms inside a magnetic field they will point to the north pole or the south pole, all of them will point in the same direction, but I'm not sure which one. The idea is that if see a film of the universe with the time in reverse, the laws will be exactly the same. You will notice some global problems, like an egg getting magically rebuild after it is scattered on a wall. But if you look at each particle individually you will not notice anything strange. This is called the T symmetry. https://en.wikipedia.org/wiki/T-symmetry https://en.wikipedia.org/wiki/T-symmetry The problem is that the T symmetry is not a real symmetry. There are some tiny details that are different when you look carefully. This is totally not related to the broken egg problem. Just ignore the eggs. I'm not sure now about the details, but IIRC when you reverse the velocities of all the particles, then the electromagnets have the current flowing in the other direction. But the atom nuclei have a tiny magnetic moment, due to spin, that is not reversed. So [mmm] and then [mmm] so it's obvious that all the atoms nuclei have to be ellipsoids, not have a pear shape. They have to be symmetric in the direction of the spin. They apparently measured (indirectly) the shape of some atom nuclei and they have a pear shape, so it's a new experimental prove that the T symmetry is broken. IIRC all the previous proof were more indirect. If you see the film of the universe in the reverse direction, you can look carefully at this atoms inside an electromagnet and see that the pointy part of the pear is in the wrong direction. (Assuming they hide all the eggs and other objects than can give you an easier clue.) This operation T is called time reversal, and it gives a lot of useful information about systems where the broken part of the symmetry is negligible. In particular if you want to calculate the properties of a small molecule, you can use this property to reduce a lot the amount of calculations. You may be wondering how is this related to Time Travel ... me too. Probably is the linkbait version of Time Reversal, that is a too nice name for a simple operation.