WEBVTT

00:00.000 --> 00:18.000
Why are general relativity and quantum physics incompatible?

00:18.000 --> 00:24.000
How is it that macroworld and microworld work according to different rules?

00:24.000 --> 00:29.000
Since we are also made of atoms, what does this say about us?

00:29.000 --> 00:34.000
Yeah, this is one of the great problems of modern physics,

00:34.000 --> 00:36.000
is putting gravity and quantum mechanics together.

00:36.000 --> 00:40.000
So, I don't think anyone would say it's impossible to put them together,

00:40.000 --> 00:42.000
but no one has succeeded yet.

00:42.000 --> 00:46.000
And part of it, it just is different length scales,

00:46.000 --> 00:51.000
that general relativity, the effects normally we would only see

00:51.000 --> 00:55.000
on very, very large scales of the distance of stars.

00:55.000 --> 01:00.000
Although, if you want to get extremely accurate,

01:00.000 --> 01:03.000
then you actually do need to pay attention to general relativity.

01:03.000 --> 01:06.000
The GPS satellite system that we all use,

01:06.000 --> 01:09.000
actually uses general relativity in the calculations,

01:09.000 --> 01:13.000
and that's because they want to get extremely accurate to many decimal places.

01:13.000 --> 01:15.000
On the other hand, quantum mechanics,

01:15.000 --> 01:19.000
typically the effects are even much smaller scale than us,

01:19.000 --> 01:22.000
down at the atomic level.

01:22.000 --> 01:25.000
And so, part of it is just the mismatch between those.

01:25.000 --> 01:28.000
Now, a lot of the normal physics that we experience

01:28.000 --> 01:33.000
is averaged over many, many particles.

01:33.000 --> 01:36.000
And so, even in one gram of material,

01:36.000 --> 01:39.000
you might have 10 to the 23rd atoms,

01:39.000 --> 01:42.000
which is one with 23 zeros,

01:42.000 --> 01:44.000
and just an enormous number of atoms.

01:44.000 --> 01:47.000
And so, almost always at the level that we live at,

01:47.000 --> 01:49.000
which we call the macroscopic,

01:49.000 --> 01:52.000
we're seeing average behavior of a lot of things.

01:52.000 --> 01:56.000
And so, we don't see these tiny quantum mechanical effects.

01:56.000 --> 01:58.000
Now, that's not always true, actually.

01:58.000 --> 02:01.000
You can, I study things called Bose condensates,

02:01.000 --> 02:05.000
and you can have a Bose condensate or a superconductor

02:05.000 --> 02:09.000
which show quantum mechanical effects even in large scale systems.

02:09.000 --> 02:12.000
And so, it's not quite accurate to say that quantum mechanics

02:12.000 --> 02:14.000
is always only at the small scale,

02:14.000 --> 02:15.000
but typically it is.

02:15.000 --> 02:18.000
And so, we typically don't worry about it.

02:18.000 --> 02:20.000
But the other thing I would say is,

02:20.000 --> 02:23.000
special relativity and general relativity

02:23.000 --> 02:26.000
are considered by most scientists

02:26.000 --> 02:29.000
to be very well understood,

02:29.000 --> 02:32.000
in some sense, classical theories.

02:32.000 --> 02:35.000
That they don't involve anything

02:35.000 --> 02:38.000
that's really conceptually hard for us philosophically.

02:38.000 --> 02:41.000
Now, we have to change our concept of time,

02:41.000 --> 02:44.000
but if you can do that,

02:44.000 --> 02:46.000
then actually special relativity and general relativity

02:46.000 --> 02:48.000
are not that problematic.

02:48.000 --> 02:50.000
Quantum mechanics, on the other hand,

02:50.000 --> 02:51.000
people still argue about.

02:51.000 --> 02:53.000
I was just at a meeting a couple of weeks ago

02:53.000 --> 02:56.000
where we were five Christian scientists

02:56.000 --> 02:58.000
debating about the meaning of quantum mechanics

02:58.000 --> 03:00.000
and didn't agree between ourselves.

03:00.000 --> 03:03.000
Because quantum mechanics is still not considered

03:03.000 --> 03:05.000
to be a fully understood theory.

03:05.000 --> 03:08.000
So, we can do a lot of things with it,

03:08.000 --> 03:10.000
calculate things extremely accurately,

03:10.000 --> 03:12.000
and yet still debate about what it all means

03:12.000 --> 03:14.000
and what's really going on with it.

03:14.000 --> 03:16.000
So, part of the reason why putting gravity

03:16.000 --> 03:18.000
and quantum mechanics together is hard

03:18.000 --> 03:20.000
is because we still don't entirely understand

03:20.000 --> 03:22.000
quantum mechanics in some ways

03:22.000 --> 03:24.000
as to what's really going on at the basic level.