0
00:00:00,000 --> 00:00:11,000
This is NASA's Space Power Facility near Cleveland, Ohio, and it is the world's biggest vacuum

1
00:00:11,000 --> 00:00:16,000
chamber. It's used to test spacecraft in the conditions of outer space, and it does that

2
00:00:16,000 --> 00:00:26,000
by pumping out the 30 tonnes of air in this chamber until there are about 2g left. And

3
00:00:26,000 --> 00:00:31,000
it's kind of got an eccentric construction, which is part of its history. It was built

4
00:00:31,000 --> 00:00:38,000
in the 1960s as a nuclear test facility to test nuclear propulsion systems, and that

5
00:00:38,000 --> 00:00:43,000
meant that they built it out of aluminium to make the radiation easier to deal with.

6
00:00:43,000 --> 00:00:49,000
Aluminium is not the best thing, the strongest material to build a vacuum chamber out of.

7
00:00:49,000 --> 00:00:55,000
So they built an outer concrete skin, which is part radiation shielding and part an external

8
00:00:55,000 --> 00:01:01,000
pressure vessel, so that this thing can take the force that's present on the outside when

9
00:01:01,000 --> 00:01:12,000
it's pumped out to the conditions of outer space.

10
00:01:12,000 --> 00:01:18,000
Galileo's experiment was simple. He took a heavy object and a light one, and dropped

11
00:01:18,000 --> 00:01:36,000
them at the same time to see which fell fastest.

12
00:01:36,000 --> 00:01:41,000
In this case, the feathers fell to the ground at a slower rate than the bowling ball because

13
00:01:41,000 --> 00:01:48,000
of air resistance.

14
00:02:12,000 --> 00:02:18,000
It takes three hours to pump out the 800,000 cubic feet of air from the chamber.

15
00:02:18,000 --> 00:02:22,000
We dropped two millitour in the last 30 minutes.

16
00:02:22,000 --> 00:02:26,000
But once it's complete, there's a near perfect vacuum inside.

17
00:02:26,000 --> 00:02:35,000
6104 manual, 10% open. Station one, go for drop. PCB 30-1, pressure set point at 240

18
00:02:35,000 --> 00:02:39,000
psi. We are go for drop.

19
00:02:39,000 --> 00:02:53,000
10, 9, 8, 7, 6, 5, 4, cameras on, 2, 1, release.

20
00:03:05,000 --> 00:03:27,000
They came down exactly the same.

21
00:03:27,000 --> 00:03:28,000
Wow.

22
00:03:28,000 --> 00:03:29,000
Look, look, look.

23
00:03:29,000 --> 00:03:30,000
Watch right there.

24
00:03:30,000 --> 00:03:31,000
Look at how they hit right there.

25
00:03:31,000 --> 00:03:32,000
Wow.

26
00:03:32,000 --> 00:03:33,000
Exactly.

27
00:03:33,000 --> 00:03:34,000
Back on the side.

28
00:03:34,000 --> 00:03:35,000
Exactly the same.

29
00:03:35,000 --> 00:03:36,000
Feathers don't move.

30
00:03:36,000 --> 00:03:37,000
Nothing.

31
00:03:37,000 --> 00:03:38,000
Look at that.

32
00:03:38,000 --> 00:03:39,000
Look at that.

33
00:03:39,000 --> 00:03:46,000
That's just brilliant.

34
00:03:46,000 --> 00:03:51,000
Isaac Newton would say that the ball and the feather fall because there's a force pulling

35
00:03:51,000 --> 00:03:54,000
them down, gravity.

36
00:03:54,000 --> 00:03:58,000
But Einstein imagined the scene very differently.

37
00:03:58,000 --> 00:04:02,000
The happiest thought of his life was this.

38
00:04:02,000 --> 00:04:10,000
The reason the bowling ball and the feather fall together is because they're not falling.

39
00:04:10,000 --> 00:04:12,000
They're standing still.

40
00:04:12,000 --> 00:04:20,000
There is no force acting on them at all.

41
00:04:21,000 --> 00:04:26,000
He reasoned that if you couldn't see the background, there'd be no way of knowing that the ball

42
00:04:26,000 --> 00:04:32,000
and the feathers were being accelerated towards the earth.

43
00:04:32,000 --> 00:04:35,000
So he concluded, they weren't.