The search for dark matter -- and what we've found so far | Risa Wechsler

542,882 views ใƒป 2020-01-27

TED


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Tal Hemo ืขืจื™ื›ื”: Ido Dekkers
00:12
Do you ever think about what would happen
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ื—ืฉื‘ืชื ืคืขื ืžื” ื”ื™ื” ืงื•ืจื”
00:14
if the world were a little bit different?
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ืื ื”ืขื•ืœื ื”ื™ื” ืžืขื˜ ืฉื•ื ื”?
00:17
How your life would be different
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ืื™ืš ื”ื—ื™ื™ื ืฉืœื›ื ื”ื™ื• ืฉื•ื ื™ื,
00:19
if you were born 5,000 years from now
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ืื ื”ื™ื™ืชื ื ื•ืœื“ื™ื ืœืคื ื™ 5,000 ืฉื ื”,
00:21
instead of today?
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ื‘ืžืงื•ื ืขื›ืฉื™ื•?
00:23
How history would be different
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ืื™ืš ื”ื”ื™ืกื˜ื•ืจื™ื” ื”ื™ื™ืชื” ืฉื•ื ื”,
00:25
if the continents were at different latitudes
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ืื ื”ื™ื‘ืฉื•ืช ื”ื™ื• ื‘ืงื•ื•ื™ ืจื•ื—ื‘ ืฉื•ื ื™ื,
00:27
or how life in the Solar system would have developed
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ืื• ืื™ืš ื”ื—ื™ื™ื ื‘ืžืขืจื›ืช ื”ืฉืžืฉ ื”ื™ื• ืžืชืคืชื—ื™ื,
00:31
if the Sun were 10 percent larger.
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ืื ื”ืฉืžืฉ ื”ื™ื™ืชื” ื’ื“ื•ืœื” ื™ื•ืชืจ ื‘ืขืฉืจื” ืื—ื•ื–.
00:35
Well, playing with these kinds of possibilities
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ื•ื‘ื›ืŸ, ืœืฉื—ืง ื›ืš ืขื ืืคืฉืจื•ื™ื•ืช ื›ืืœื•,
00:38
is what I get to do for a living
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ื”ื•ื ืžื” ืฉืื ื™ ืขื•ืฉื” ืœืžื—ื™ื™ืชื™,
00:39
but with the entire universe.
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ืืš ืขื ื”ื™ืงื•ื ื›ื•ืœื•.
00:43
I make model universes in a computer.
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ืื ื™ ื™ื•ืฆืจืช ืžื•ื“ืœื™ื ืฉืœ ื™ืงื•ืžื™ื ื‘ืžื—ืฉื‘.
00:45
Digital universes that have different starting points
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ื™ืงื•ืžื™ื ืžืžื•ื—ืฉื‘ื™ื, ืฉื™ืฉ ืœื”ื ื ืงื•ื“ื•ืช ื”ืชื—ืœื” ืฉื•ื ื•ืช,
00:48
and are made of different amounts of different kinds of material.
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ื•ืฉืขืฉื•ื™ื™ื ืžื›ืžื•ื™ื•ืช ืฉื•ื ื•ืช, ืฉืœ ื—ื•ืžืจื™ื ืฉื•ื ื™ื.
00:53
And then I compare these universes to our own
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ื•ืื– ืื ื™ ืžืฉื•ื•ื” ืืช ื”ื™ืงื•ืžื™ื ื”ืืœื”, ืœืฉืœื ื•.
00:56
to see what it is made of and how it evolved.
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ื›ื“ื™ ืœืจืื•ืช ืžืžื” ื”ื•ื ืขืฉื•ื™, ื•ืื™ืš ื”ื•ื ื”ืชืคืชื—.
01:02
This process of testing models with measurements of the sky
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ื”ืชื”ืœื™ืš ื”ื–ื” ืฉืœ ื‘ื—ื™ื ืช ืžื•ื“ืœื™ื, ืขื ืžื“ื™ื“ื•ืช ืฉืœ ื”ืฉืžื™ื™ื,
01:06
has taught us a huge amount about our universe so far.
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ืœื™ืžื“ ืื•ืชื ื• ื”ืจื‘ื” ืขืœ ื”ื™ืงื•ื ืขื“ ื›ื”.
01:10
One of the strangest things we have learned
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ืื—ื“ ื”ื“ื‘ืจื™ื ื”ืžื•ื–ืจื™ื ื‘ื™ื•ืชืจ ืฉืœืžื“ื ื•,
01:12
is that most of the material in the universe
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ื”ื•ื ืฉืจื•ื‘ ื”ื—ื•ืžืจ ื‘ื™ืงื•ื,
01:15
is made of something entirely different than you and me.
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ืขืฉื•ื™ ืžืžืฉื”ื• ืื—ืจ ืœื’ืžืจื™ ืžืžื›ื ื•ืžืžื ื™.
01:20
But without it,
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ืืš ื‘ืœืขื“ื™ื•,
01:23
the universe as we know it wouldn't exist.
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ื”ื™ืงื•ื ื›ืคื™ ืฉืื ื• ืžื›ื™ืจื™ื ืื•ืชื•, ืœื ื”ื™ื” ืงื™ื™ื.
01:28
Everything we can see with telescopes
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ื›ืœ ื“ื‘ืจ ืฉืื ื• ื™ื›ื•ืœื™ื ืœืจืื•ืช ืขื ื˜ืœืกืงื•ืคื™ื,
01:32
makes up just about 15 percent of the total mass in the universe.
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ื”ื•ื ื‘ืกืš-ื”ื›ืœ 15% ืžืžืกืช ื”ื™ืงื•ื.
01:38
Everything else, 85 percent of it,
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ื›ืœ ื”ืฉืืจ, 85% ืžืžื ื•,
01:42
doesn't emit or absorb light.
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ืœื ืคื•ืœื˜ ืื• ืงื•ืœื˜ ืื•ืจ.
01:45
We can't see it with our eyes,
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ืื ื• ืœื ื™ื›ื•ืœื™ื ืœืจืื•ืช ืื•ืชื• ื‘ืขื™ื ื™ื™ื ืฉืœื ื•,
01:48
we can't detect it with radio waves
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ืื ื• ืœื ื™ื›ื•ืœื™ื ืœื–ื”ื•ืช ืื•ืชื• ืขื ื’ืœื™ ืจื“ื™ื•,
01:51
or microwaves or any other kind of light.
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ืื• ื’ืœื™ ืžื™ืงืจื• ืื• ื›ืœ ืกื•ื’ ืื—ืจ ืฉืœ ืื•ืจ.
01:55
But we know it is there
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ืื‘ืœ ืื ื—ื ื• ื™ื•ื“ืขื™ื ืฉื”ื•ื ืฉื,
01:57
because of its influence on what we can see.
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ื‘ื’ืœืœ ื”ื”ืฉืคืขื” ืฉืœื• ืขืœ ืžื” ืฉืื ื• ืžืกื•ื’ืœื™ื ืœืจืื•ืช.
02:01
It's a little bit like,
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ื–ื” ืงืฆืช ื›ืžื•,
02:02
if you wanted to map the surface of our planet
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ืื ื”ื™ื™ืชื ืจื•ืฆื™ื ืœืžืคื•ืช ืืช ืคื ื™ ื›ื“ื•ืจ-ื”ืืจืฅ
02:04
and everything on it
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ื•ืืช ื›ืœ ืžื” ืฉืขืœื™ื•,
02:06
using this picture of the Earth from space at night.
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ื‘ืืžืฆืขื•ืช ื”ืชืžื•ื ื” ื”ื–ื• ืฉืœ ื›ื“ื•ืจ-ื”ืืจืฅ ืžื”ื—ืœืœ ื‘ืœื™ืœื”.
02:11
You get some clues from where the light is,
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ื™ืฉื ื ืจืžื–ื™ื ืžื”ื™ื›ืŸ ืžื’ื™ืข ื”ืื•ืจ,
02:14
but there's a lot that you can't see,
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ืืš ื™ืฉ ื”ืžื•ืŸ ืฉืืชื ืœื ื™ื›ื•ืœื™ื ืœืจืื•ืช,
02:16
everything from people to mountain ranges.
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ื”ื—ืœ ืžืื ืฉื™ื, ืœืจื›ืกื™ ื”ืจื™ื.
02:19
And you have to infer what is there from these limited clues.
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ื•ืขืœื™ื›ื ืœื”ืกื™ืง ืžื” ื ืžืฆื ืฉื ืžื”ืจืžื–ื™ื ื”ืžืขื˜ื™ื ื”ืœืœื•.
02:25
We call this unseen stuff "dark matter."
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ืื ื• ืงื•ืจืื™ื ืœื“ื‘ืจ ื”ื‘ืœืชื™-ื ืจืื” ื”ื–ื” "ื—ื•ืžืจ ืืคืœ".
02:29
Now, a lot of people have heard of dark matter,
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ืขื›ืฉื™ื•, ื”ืจื‘ื” ืื ืฉื™ื ืฉืžืขื• ืขืœ ื—ื•ืžืจ ืืคืœ,
02:32
but even if you have heard of it,
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ืืš ืืคื™ืœื• ืื ืฉืžืขืชื ืขืœื™ื•,
02:34
it probably seems abstract,
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ื”ื•ื ื‘ื•ื•ื“ืื™ ื ืฉืžืข ืžื•ืคืฉื˜,
02:38
far away, probably even irrelevant.
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ืจื—ื•ืง, ืกื‘ื™ืจ ืœื”ื ื™ื— ืฉืืคื™ืœื• ืœื ืจืœื•ื•ื ื˜ื™.
02:42
Well, the interesting thing is,
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ื•ื‘ื›ืŸ, ื”ื“ื‘ืจ ื”ืžืขื ื™ื™ืŸ ื”ื•ื,
02:45
dark matter is all around us
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ื”ื—ื•ืžืจ ื”ืืคืœ ื ืžืฆื ืกื‘ื™ื‘ื ื•,
02:48
and probably right here.
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ื•ืงืจื•ื‘ ืœื•ื•ื“ืื™ ืฉืžืžืฉ ื›ืืŸ.
02:50
In fact, dark matter particles
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ืœืžืขืฉื”, ื”ื—ืœืงื™ืงื™ื ืฉืœ ื”ื—ื•ืžืจ ื”ืืคืœ,
02:52
are probably going through your body right now
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ื›ื ืจืื” ืขื•ื‘ืจื™ื ื“ืจืš ื’ื•ืคื›ื ื‘ืจื’ืข ื–ื”.
02:56
as you sit in this room.
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ื›ืฉืืชื ื™ื•ืฉื‘ื™ื ื‘ื—ื“ืจ ื”ื–ื”.
02:58
Because we are on Earth
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ืžื›ื™ื•ื•ืŸ ืฉืื ื• ื‘ื›ื“ื•ืจ-ื”ืืจืฅ,
02:59
and Earth is spinning around the Sun,
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ื•ื›ื“ื•ืจ-ื”ืืจืฅ ืกื•ื‘ื‘ ืกื‘ื™ื‘ ื”ืฉืžืฉ,
03:01
and the Sun is hurtling through our galaxy
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ื•ื”ืฉืžืฉ ื ืขื” ืœืื•ืจืš ื”ื’ืœืงืกื™ื” ืฉืœื ื•,
03:04
at about half a million miles per hour.
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ื‘ืžื”ื™ืจื•ืช ืฉืœ 800 ืืœืฃ ืงืž"ืฉ.
03:07
But dark matter doesn't bump into us,
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ืืš ื”ื—ื•ืžืจ ื”ืืคืœ ืื™ื ื• ืžืชื ื’ืฉ ื‘ื ื•,
03:09
it just goes right through us.
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ื”ื•ื ืขื•ื‘ืจ ื“ืจื›ื™ื ื•.
03:12
So how do we figure out more about this?
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ืื– ืื™ืš ืื ื—ื ื• ืžื’ืœื™ื ื™ื•ืชืจ ืขืœื™ื•?
03:17
What is it,
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ืžื” ื”ื•ื,
03:18
and what does it have to do with our existence?
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ื•ืžื” ื”ืงืฉืจ ืฉืœื• ืืœ ื”ืงื™ื•ื ืฉืœื ื•?
03:20
Well, in order to figure out how we came to be,
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ื•ื‘ื›ืŸ, ืขืœ ืžื ืช ืœื’ืœื•ืช ืื™ืš ื ื•ืฆืจื ื•,
03:25
we first need to understand how our galaxy came to be.
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ืขืœื™ื ื• ืงื•ื“ื ื›ืœ ืœื’ืœื•ืช ืื™ืš ื”ื’ืœืงืกื™ื” ืฉืœื ื• ื ื•ืฆืจื”.
03:29
This is a picture of our galaxy, the Milky Way, today.
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ื–ื• ืชืžื•ื ื” ืฉืœ ื”ื’ืœืืงืกื™ื” ืฉืœื ื•, ืฉื‘ื™ืœ ื”ื—ืœื‘, ื”ื™ื•ื.
03:34
What did it look like 10 billion years in the past
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ืื™ืš ื”ื™ื ื ืจืืชื” ืœืคื ื™ 10 ืžื™ืœื™ืืจื“ ืฉื ื”
03:36
or what would it look like 10 billion years in the future?
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ืื• ืื™ืš ื”ื™ื ืชื™ืจืื” ืขื•ื“ 10 ืžื™ืœื™ืืจื“ ืฉื ื”?
03:40
What about the stories
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ืžื” ืœื’ื‘ื™ ื”ืกื™ืคื•ืจื™ื,
03:42
of the hundreds of millions of other galaxies
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ืฉืœ ืžืื•ืช ืžื™ืœื™ื•ื ื™ ื’ืœืงืกื™ื•ืช ืื—ืจื•ืช
03:45
that we've already mapped out with large surveys of the sky?
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ืฉื›ื‘ืจ ืžื™ืคื™ื ื•, ื‘ืกืงืจื™ื ื’ื“ื•ืœื™ื ืฉืœ ื”ืฉืžื™ื™ื?
03:49
How would their histories be different
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ืื™ืš ื”ื”ื™ืกื˜ื•ืจื™ื” ืฉืœื”ืŸ ืชื”ื™ื” ืฉื•ื ื”,
03:51
if the universe was made of something else
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ืื ื”ื™ืงื•ื ื”ื™ื” ืขืฉื•ื™ ืžืžืฉื”ื• ืื—ืจ,
03:54
or if there was more or less matter in it?
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ืื• ืื ื”ื™ื” ื‘ื• ื™ื•ืชืจ ืื• ืคื—ื•ืช ื—ื•ืžืจ?
03:57
So the interesting thing about these model universes
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ืื– ื”ื“ื‘ืจ ื”ืžืขื ื™ื™ืŸ ื‘ืžื•ื“ืœื™ื ืฉืœ ื”ื™ืงื•ืžื™ื ื”ืœืœื•,
04:01
is that they allow us to test these possibilities.
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ื”ื•ื ืฉื”ื ืžืืคืฉืจื™ื ืœื ื• ืœื‘ื—ื•ืŸ ืืช ื”ืืคืฉืจื•ื™ื•ืช ื”ืืœื”.
04:05
Let's go back to the first moment of the universe --
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ื‘ื•ืื• ื ื—ื–ื•ืจ ืœืจื’ืข ื”ืจืืฉื•ืŸ ืฉืœ ื”ื™ืงื•ื --
04:11
just a fraction of a second after the big bang.
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ืจืง ื—ืœืงื™ืง ืฉื ื™ื” ืื—ืจื™ ื”ืžืคืฅ ื”ื’ื“ื•ืœ.
04:17
In this first moment,
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ื‘ืจื’ืข ื”ืจืืฉื•ืŸ ื”ื–ื”,
04:19
there was no matter at all.
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ืœื ื”ื™ื” ื—ื•ืžืจ ื›ืœืœ.
04:21
The universe was expanding very fast.
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ื”ื™ืงื•ื ื”ืชืจื—ื‘ ืžื”ืจ ืžืื•ื“.
04:25
And quantum mechanics tells us
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ื•ืžื›ื ื™ืงืช ื”ืงื•ื•ื ื˜ื™ื ืื•ืžืจืช ืœื ื•,
04:28
that matter is being created and destroyed
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ืฉื—ื•ืžืจ ื ื•ืฆืจ, ื•ื ื”ืจืก,
04:31
all the time, in every moment.
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ื›ืœ ื”ื–ืžืŸ, ื‘ื›ืœ ืจื’ืข ื ืชื•ืŸ.
04:34
At this time, the universe was expanding so fast
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ื‘ื–ืžืŸ ื”ื–ื”, ื”ื™ืงื•ื ื”ืชืจื—ื‘ ื›ืœ-ื›ืš ืžื”ืจ,
04:36
that the matter that got created couldn't get destroyed.
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ืฉื”ื—ื•ืžืจ ืฉื ื•ืฆืจ ืœื ื™ื›ื•ืœ ื”ื™ื” ืœื”ื™ื”ืจืก.
04:40
And thus we think that all of the matter was created during this time.
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ื•ืœื›ืŸ ืื ื—ื ื• ื—ื•ืฉื‘ื™ื ืฉื›ืœ ื”ื—ื•ืžืจ, ื ื•ืฆืจ ื‘ื–ืžืŸ ื”ื–ื”.
04:45
Both the dark matter
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ื’ื ื”ื—ื•ืžืจ ื”ืืคืœ,
04:47
and the regular matter that makes up you and me.
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ื•ื’ื ื”ื—ื•ืžืจ ื”ืจื’ื™ืœ, ืฉืžืจื›ื™ื‘ ืื•ืชื™ ื•ืืชื›ื.
04:52
Now, let's go a little bit further
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ืขื›ืฉื™ื•, ื‘ื•ืื• ื ืœืš ืžืขื˜ ืงื“ื™ืžื”,
04:54
to a time after the matter was created,
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ืœื–ืžืŸ ืื—ืจื™ ืฉื”ื—ื•ืžืจ ื ื•ืฆืจ,
04:57
after protons and neutrons formed,
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ืœืื—ืจ ืฉืคืจื•ื˜ื•ื ื™ื ื•ื ื™ื•ื˜ืจื•ื ื™ื ื ื•ืฆืจื•,
04:59
after hydrogen formed,
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ืื—ืจื™ ืฉืžื™ืžืŸ ื ื•ืฆืจ,
05:01
about 400,000 years after the big bang.
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ื‘ืขืจืš 400,000 ืฉื ื™ื ืื—ืจื™ ื”ืžืคืฅ ื”ื’ื“ื•ืœ.
05:05
The universe was hot and dense and really smooth
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ื”ื™ืงื•ื ื”ื™ื” ืœื•ื”ื˜ ื•ื“ื—ื•ืก, ื•ืžืื•ื“ ื—ืœืง,
05:09
but not perfectly smooth.
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ืืš ืœื ื—ืœืง ืœื’ืžืจื™.
05:12
This image, taken with a space telescope called the Planck satellite,
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ื”ืชืžื•ื ื” ื”ื–ื•, ืฉื ืœืงื—ื” ื‘ืืžืฆืขื•ืช ื˜ืœืกืงื•ืค ื—ืœืœ ื”ื ืงืจื ืœื•ื•ื™ื™ืŸ ืคืœืื ืง,
05:17
shows us the temperature of the universe
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ืžืจืื” ืœื ื• ืืช ื”ื˜ืžืคืจื˜ื•ืจื” ืฉืœ ื”ื™ืงื•ื
05:19
in all directions.
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ื‘ื›ืœ ื”ื›ื™ื•ื•ื ื™ื.
05:22
And what we see
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ื•ืžื” ืฉืื ื• ืจื•ืื™ื
05:23
is that there were places that were a little bit hotter
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ื”ื•ื ืฉื™ืฉื ื ืื™ื–ื•ืจื™ื ืฉื”ื™ื• ื—ืžื™ื ื™ื•ืชืจ,
05:26
and denser than others.
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ื•ื“ื—ื•ืกื™ื ื™ื•ืชืจ ืžืื—ืจื™ื.
05:28
The spots in this image
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ื”ื ืงื•ื“ื•ืช ื‘ืชืžื•ื ื” ื”ื–ื•,
05:30
represent places where there was more or less mass in the early universe.
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ืžื™ื™ืฆื’ื•ืช ืื™ื–ื•ืจื™ื ื‘ื”ื ื”ื™ื” ืคื—ื•ืช ืื• ื™ื•ืชืจ ืžืกื” ื‘ื™ืงื•ื ื”ืงื“ื•ื.
05:37
Those spots got big because of gravity.
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ื”ื ืงื•ื“ื•ืช ื”ืืœื• ื’ื“ืœื• ื‘ื’ืœืœ ื›ื•ื— ื”ื›ื‘ื™ื“ื”.
05:41
The universe was expanding and getting less dense overall
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ื”ื™ืงื•ื ื”ืชืจื—ื‘ ื•ื”ืคืš ืœื“ื—ื•ืก ืคื—ื•ืช,
05:45
over the last 13.8 billion years.
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ืœืื•ืจืš 13.8 ืžื™ืœื™ืืจื“ ืฉื ื”.
05:49
But gravity worked hard in those spots
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ืื‘ืœ ื›ื•ื— ื”ื›ื‘ื™ื“ื” ืขื‘ื“ ืงืฉื”, ื‘ื ืงื•ื“ื•ืช ื”ืืœื”,
05:52
where there was a little bit more mass
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ื”ื™ื›ืŸ ืฉื”ื™ื™ืชื” ืงืฆืช ื™ื•ืชืจ ืžืกื”,
05:54
and pulled more and more mass into those regions.
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ื•ืžืฉืš ื™ื•ืชืจ ื•ื™ื•ืชืจ ืžืกื”, ืืœ ืื•ืชื ืื™ื–ื•ืจื™ื.
05:59
Now, all of this is a little hard to imagine,
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ืขื›ืฉื™ื•, ืงืฉื” ืงืฆืช ืœื“ืžื™ื™ืŸ ืืช ื›ืœ ื–ื”,
06:01
so let me just show you what I am talking about.
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ืื– ืชื ื• ืœื™ ืœื”ืจืื•ืช ืœื›ื ืขืœ ืžื” ืื ื™ ืžื“ื‘ืจืช.
06:05
Those computer models I mentioned allow us to test these ideas,
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ื”ืžื•ื“ืœื™ื ื”ืžืžื•ื—ืฉื‘ื™ื ืฉืฆื™ื™ื ืชื™, ืžืืคืฉืจื™ื ืœื ื• ืœื‘ื—ื•ืŸ ืืช ื”ืจืขื™ื•ื ื•ืช ื”ืืœื”,
06:08
so let's take a look at one of them.
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ืื– ื‘ื•ืื• ื ืฆืคื” ื‘ืื—ื“ ืžื”ื.
06:11
This movie, made by my research group,
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ื”ืกืจื˜ ื”ื–ื”, ืฉื ื•ืฆืจ ืขืœ-ื™ื“ื™ ืงื‘ื•ืฆืช ื”ืžื—ืงืจ ืฉืœื™,
06:14
shows us what happened to the universe after its earliest moments.
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ืžืžื—ื™ืฉ ืœื ื• ืžื” ืืจืข ืœื™ืงื•ื ืื—ืจื™ ืจื’ืขื™ื• ื”ืจืืฉื•ื ื™ื.
06:20
You see the universe started out pretty smooth,
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ืืชื ืจื•ืื™ื, ื”ื™ืงื•ื ื”ืชื—ื™ืœ ื“ื™ ื—ืœืง,
06:23
but there were some regions
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ืืš ื™ืฉื ื ื›ืžื” ืื™ื–ื•ืจื™ื
06:24
where there was a little bit more material.
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ื‘ื”ื ื”ื™ื” ืงืฆืช ื™ื•ืชืจ ื—ื•ืžืจ.
06:27
Gravity turned on and brought more and more mass
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ื›ื•ื— ื”ื›ื‘ื™ื“ื” ื”ื•ืคืขืœ ื•ื”ื‘ื™ื ืขื•ื“ ื•ืขื•ื“ ืžืกื”,
06:31
into those spots that started out with a little bit extra.
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ืืœ ืชื•ืš ื”ื ืงื•ื“ื•ืช ื”ืœืœื• ืฉื”ืชื—ื™ืœื• ืขื ืงืฆืช ื™ื•ืชืจ ืขื•ื“ืฃ.
06:36
Over time,
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ื‘ืžืฉืš ื”ื–ืžืŸ,
06:37
you get enough stuff in one place
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ืžืชืงื‘ืœ ืžืกืคื™ืง ื—ื•ืžืจ ื‘ืžืงื•ื ืื—ื“,
06:40
that the hydrogen gas,
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ืขื“ ืฉื’ื– ื”ืžื™ืžืŸ,
06:41
which was initially well mixed with the dark matter,
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ืฉื”ื™ื” ืชื—ื™ืœื” ืžืขื•ืจื‘ื‘ ื”ื™ื˜ื‘ ืขื ื—ื•ืžืจ ืืคืœ,
06:44
starts to separate from it,
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ืžืชื—ื™ืœ ืœื”ืชื ืชืง ืžืžื ื•,
06:46
cool down, form stars,
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ืžืชืงืจืจ, ื™ื•ืฆืจ ื›ื•ื›ื‘ื™ื,
06:49
and you get a small galaxy.
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ื•ืžืชืงื‘ืœืช ื’ืœืืงืกื™ื” ืงื˜ื ื”.
06:51
Over time, over billions and billions of years,
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ื‘ืžืฉืš ื”ื–ืžืŸ, ืœืื•ืจืš ืžื™ืœื™ืืจื“ื™ื ืขืœ ื’ื‘ื™ ืžื™ืœื™ืืจื“ื™ื ืฉืœ ืฉื ื™ื,
06:54
those small galaxies crash into each other
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ื”ื’ืœืืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื”ืืœื” ืžืชื ื’ืฉื•ืช ืื—ืช ื‘ืฉื ื™ื”,
06:57
and merge and grow to become larger galaxies,
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ื•ืžืชืžื–ื’ื•ืช ืœื’ืœืงืกื™ื•ืช ื’ื“ื•ืœื•ืช ื™ื•ืชืจ,
07:00
like our own galaxy, the Milky Way.
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ื‘ื“ื•ืžื” ืœื’ืœืงืกื™ื” ืฉืœื ื•, ืฉื‘ื™ืœ ื”ื—ืœื‘.
07:03
Now, what happens if you don't have dark matter?
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ืขื›ืฉื™ื•, ืžื” ืงื•ืจื” ืื ืื™ืŸ ืœื›ื ื—ื•ืžืจ ืืคืœ?
07:08
If you don't have dark matter,
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ืื ืื™ืŸ ืœื›ื ื—ื•ืžืจ ืืคืœ,
07:10
those spots never get clumpy enough.
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ื”ื›ืชืžื™ื ื”ืืœื” ืœืขื•ืœื ืœื ืžืฆื˜ื‘ืจื™ื ืžืกืคื™ืง.
07:14
It turns out, you need at least a million times the mass of the Sun
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ืžืกืชื‘ืจ ืฉื“ืจื•ืฉ ืคื™ ืžื™ืœื™ื•ืŸ ืžืžืกืช ื”ืฉืžืฉ,
07:19
in one dense region,
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ื‘ืื™ื–ื•ืจ ื“ื—ื•ืก ืื—ื“,
07:20
before you can start forming stars.
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ืœื™ืฆื™ืจืช ื›ื•ื›ื‘ื™ื.
07:23
And without dark matter,
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ื•ืœืœื ื—ื•ืžืจ ืืคืœ,
07:25
you never get enough stuff in one place.
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ืœืขื•ืœื ืœื ืžืชืงื‘ืœืช ืžืกืคื™ืง ืžืกื” ื‘ืžืงื•ื ืื—ื“.
07:28
So here, we're looking at two universes, side by side.
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ืื– ื”ื ื”, ืื ื• ืžืกืชื›ืœื™ื ืขืœ ืฉื ื™ ื™ืงื•ืžื™ื, ืื—ื“ ืœื™ื“ ื”ืฉื ื™.
07:33
In one of them you can see
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ื‘ืื—ื“ ืžื”ื ื ื™ืชืŸ ืœืจืื•ืช,
07:35
that things get clumpy quickly.
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ืฉื“ื‘ืจื™ื ืžืฆื˜ื‘ืจื™ื ื‘ืžื”ื™ืจื•ืช.
07:39
In that universe,
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ื‘ื™ืงื•ื ื”ื–ื”,
07:40
it's really easy to form galaxies.
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ืžืื•ื“ ืงืœ ืœื™ืฆื•ืจ ื’ืœืงืกื™ื•ืช.
07:43
In the other universe,
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ื‘ื™ืงื•ื ื”ืฉื ื™,
07:44
the things that start out like small clumps,
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ื”ื“ื‘ืจื™ื ืฉืžืชื—ื™ืœื™ื ื›ื”ืฆื˜ื‘ืจื•ื™ื•ืช ืงื˜ื ื•ืช,
07:47
they just stay really small.
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ื ืฉืืจื™ื ืžืื•ื“ ืงื˜ื ื™ื.
07:49
Not very much happens.
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ืœื ื”ืจื‘ื” ืงื•ืจื”.
07:51
In that universe, you wouldn't get our galaxy.
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ื‘ื™ืงื•ื ื”ื–ื”, ืœื ืชืงื‘ืœื• ืืช ื”ื’ืœืงืกื™ื” ืฉืœื ื•.
07:54
Or any other galaxy.
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ืื• ื›ืœ ื’ืœืงืกื™ื” ืื—ืจืช.
07:56
You wouldn't get the Milky Way,
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ืœื ืชืงื‘ืœื• ืืช ืฉื‘ื™ืœ ื”ื—ืœื‘,
07:58
you wouldn't get the Sun,
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ืœื ืชืงื‘ืœื• ืืช ื”ืฉืžืฉ,
08:00
you wouldn't get us.
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ืœื ืชืงื‘ืœื• ืื•ืชื ื•.
08:02
We just couldn't exist in that universe.
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ืื ื—ื ื• ืคืฉื•ื˜ ืœื ื”ื™ื™ื ื• ืžืชืงื™ื™ืžื™ื, ื‘ื™ืงื•ื ื”ื–ื”.
08:07
OK, so this crazy stuff, dark matter,
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ืื•ืงื™ื™, ืื– ื”ื“ื‘ืจ ื”ืžืฉื•ื’ืข ื”ื–ื”, ื—ื•ืžืจ ืืคืœ,
08:10
it's most of the mass in the universe,
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ื”ื•ื ืจื•ื‘ ืžืกืช ื”ื™ืงื•ื,
08:12
it's going through us right now, we wouldn't be here without it.
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ื”ื•ื ืขื•ื‘ืจ ื“ืจื›ื™ื ื• ืžืžืฉ ืขื›ืฉื™ื•, ืœื ื”ื™ื™ื ื• ืžืชืงื™ื™ืžื™ื ื‘ืœืขื“ื™ื•.
ืžื” ื”ื•ื?
08:15
What is it?
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08:17
Well, we have no idea.
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ื•ื‘ื›ืŸ, ืื™ืŸ ืœื ื• ืžื•ืฉื’.
08:18
(Laughter)
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(ืฆื—ื•ืง)
08:21
But we have a lot of educated guesses,
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ืืš ื™ืฉ ืœื ื• ื”ืžื•ืŸ ื ื™ื—ื•ืฉื™ื ืžื•ืฉื›ืœื™ื,
08:24
and a lot of ideas for how to find out more.
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ื•ื”ืžื•ืŸ ืจืขื™ื•ื ื•ืช ืœืื™ืš ืœื’ืœื•ืช ืขื•ื“.
08:27
So, most physicists think that dark matter is a particle,
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ืื–, ืจื•ื‘ ื”ืคื™ื–ื™ืงืื™ื ื—ื•ืฉื‘ื™ื ืฉื”ื—ื•ืžืจ ื”ืืคืœ ื”ื•ื ื—ืœืงื™ืง,
08:32
similar in many ways to the subatomic particles that we know of,
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ื“ื•ืžื” ื‘ื”ืžื•ืŸ ืžื•ื‘ื ื™ื ืœื—ืœืงื™ืงื™ื ืชืช-ืื˜ื•ืžื™ื™ื ืฉืื ื• ืžื›ื™ืจื™ื,
08:35
like protons and neutrons and electrons.
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ื›ืžื• ืคืจื•ื˜ื•ื ื™ื ื•ื ื™ื•ื˜ืจื•ื ื™ื ื•ืืœืงื˜ืจื•ื ื™ื.
08:38
Whatever it is,
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ืžื” ืฉื”ื•ื ืœื ื™ื”ื™ื”,
08:39
it behaves very similarly with respect to gravity.
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ื”ื•ื ืžืชื ื”ื’ ื‘ืฆื•ืจื” ื“ื•ืžื” ืœื”ื ื‘ื™ื—ืก ืœื›ื•ื— ื”ืžืฉื™ื›ื”.
08:44
But it doesn't emit or absorb light,
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ืืš ื”ื•ื ืื™ื ื• ืคื•ืœื˜ ืื• ืงื•ืœื˜ ืื•ืจ,
08:47
and it goes right through normal matter,
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ื•ื”ื•ื ืขื•ื‘ืจ ื”ื™ืฉืจ ื“ืจืš ื—ื•ืžืจ ืจื’ื™ืœ,
08:49
as if it wasn't even there.
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ื›ืื™ืœื• ืฉื”ื•ื ืื™ื ื• ืฉื ื›ืœืœ.
08:52
We'd like to know what particle it is.
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ืื ื—ื ื• ืจื•ืฆื™ื ืœื“ืขืช ืื™ื–ื” ื—ืœืงื™ืง ื–ื”.
08:54
For example, how heavy is it?
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ืœื“ื•ื’ืžื, ื›ืžื” ื›ื‘ื“ ื”ื•ื?
08:57
Or, does anything at all happen if it interacts with normal matter?
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ืื• ื”ืื ืžืฉื”ื• ืžืชืจื—ืฉ ื›ืœืœ ื‘ืžืคื’ืฉ ื‘ื™ื ื• ืœื‘ื™ืŸ ื—ื•ืžืจ ืจื’ื™ืœ?
09:02
Physicists have lots of great ideas for what it could be,
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ืœืคื™ื–ื™ืงืื™ื ื™ืฉ ื”ืžื•ืŸ ืจืขื™ื•ื ื•ืช ืžืขื•ืœื™ื ืœืžื” ื”ื•ื ื™ื›ื•ืœ ืœื”ื™ื•ืช,
09:05
they're very creative.
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ื”ื ืžืื•ื“ ื™ืฆื™ืจืชื™ื™ื.
09:07
But it's really hard,
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ืืš ื–ื” ืžืื•ื“ ืงืฉื”,
09:09
because those ideas span a huge range.
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ืžื›ื™ื•ื•ืŸ ืฉื”ืจืขื™ื•ื ื•ืช ื”ื ืจื‘ื™ื ื•ืฉื•ื ื™ื ื–ื” ืžื–ื”.
09:12
It could be as small as the smallest subatomic particles,
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ืื•ืœื™ ื”ื•ื ืงื˜ืŸ ื›ืžื• ื”ื—ืœืงื™ืง ื”ืชืช-ืื˜ื•ืžื™ ื”ืงื˜ืŸ ื‘ื™ื•ืชืจ,
09:16
or it could be as large as the mass of 100 Suns.
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ืื• ืฉื”ื•ื ื™ื›ื•ืœ ืœื”ื™ื•ืช ื’ื“ื•ืœ ื›ืžื• ืžืกื” ืฉืœ 100 ืฉืžืฉื•ืช.
09:20
So, how do we figure out what it is?
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ืื–, ืื™ืš ื ื’ืœื” ืžื” ื–ื”?
09:24
Well, physicists and astronomers
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ื•ื‘ื›ืŸ, ืœืคื™ื–ื™ืงืื™ื ื•ืืกื˜ืจื•ื ื•ืžื™ื,
09:26
have a lot of ways to look for dark matter.
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ื™ืฉ ื”ืจื‘ื” ื“ืจื›ื™ื ืœื—ืคืฉ ืื—ืจ ื—ื•ืžืจ ืืคืœ.
09:30
One of the things we're doing is building sensitive detectors
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ืื—ื“ ื”ื“ื‘ืจื™ื ืฉืื ื• ืขื•ืฉื™ื ื”ื•ื ืœื‘ื ื•ืช ืงื•ืœื˜ื ื™ื ืจื’ื™ืฉื™ื,
09:34
in deep underground mines,
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ื‘ืžื›ืจื•ืช ืชืช-ืงืจืงืขื™ื™ื ืขืžื•ืงื™ื,
09:37
waiting for the possibility
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ืžื—ื›ื™ื ืœืืคืฉืจื•ืช,
09:40
that a dark matter particle, which goes through us and the Earth,
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ืฉื—ืœืงื™ืง ื—ื•ืžืจ ืืคืœ, ื”ืขื•ื‘ืจ ื“ืจื›ื ื• ื•ื“ืจืš ื›ื“ื•ืจ-ื”ืืจืฅ,
09:43
would hit a denser material
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ื™ืชื ื’ืฉ ื‘ื—ื•ืžืจ ื“ื—ื•ืก ื™ื•ืชืจ,
ื•ื™ืฉืื™ืจ ืื—ืจื™ื• ืขืงื‘ื•ืช ื›ืœืฉื”ืŸ.
09:46
and leave behind some trace of its passage.
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09:50
We're looking for dark matter in the sky,
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ืื ื—ื ื• ืžื—ืคืฉื™ื ื—ื•ืžืจ ืืคืœ ื‘ืฉืžื™ื™ื,
09:53
for the possibility that dark matter particles
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ื‘ืฉื‘ื™ืœ ื”ืกื™ื›ื•ื™ ืฉื—ืœืงื™ืงื™ ื—ื•ืžืจ ืืคืœ
09:55
would crash into each other
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ื™ืชื ื’ืฉื• ืื—ื“ ื‘ืฉื ื™
09:56
and create high-energy light that we could see
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ื•ื™ืฆืจื• ืื•ืจ ื‘ืขืœ ืื ืจื’ื™ื” ื’ื“ื•ืœื” ืื•ืชื• ื ื•ื›ืœ ืœืจืื•ืช
ื‘ืขื–ืจืช ื˜ืœืกืงื•ืคื™ื ืžื™ื•ื—ื“ื™ื ืœืงืจื ื™ ื’ืืžื”.
09:59
with special gamma-ray telescopes.
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10:02
We're even trying to make dark matter here on Earth,
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ืื ื—ื ื• ืืคื™ืœื• ืžื ืกื™ื ืœื™ืฆื•ืจ ื—ื•ืžืจ ืืคืœ ื›ืืŸ ื‘ื›ื“ื•ืจ-ื”ืืจืฅ,
10:06
by smashing particles together and looking for what happens,
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ืขืœ ื™ื“ื™ ืจื™ืกื•ืง ื—ืœืงื™ืงื™ื ืื—ื“ ื‘ืฉื ื™ ื•ื‘ื•ื—ื ื™ื ืžื” ืงื•ืจื”,
10:10
using the Large Hadron Collider in Switzerland.
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ื‘ืืžืฆืขื•ืช ืžืื™ืฅ ื”ื—ืœืงื™ืงื™ื ื”ื’ื“ื•ืœ ื‘ืฉืึฐื•ึทื•ื™ึฐืฅ,
10:15
Now, so far,
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ืขื›ืฉื™ื•, ืขื“ ืขื›ืฉื™ื•,
10:17
all of these experiments have taught us a lot
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ื›ืœ ื”ื ื™ืกื•ื™ื™ื ื”ืœืœื•, ืœื™ืžื“ื• ืื•ืชื ื• ื”ืจื‘ื”,
10:20
about what dark matter isn't
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ืขืœ ืžื” ื”ื—ื•ืžืจ ื”ืืคืœ ื”ื•ื ืœื.
10:22
(Laughter)
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(ืฆื—ื•ืง)
ืื‘ืœ ืขื•ื“ ืœื, ืขืœ ืžื” ื”ื•ื ื›ืŸ.
10:23
but not yet what it is.
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10:25
There were really good ideas that dark matter could have been,
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ื”ื™ื• ื”ืจื‘ื” ืจืขื™ื•ื ื•ืช ื˜ื•ื‘ื™ื ืขืœ ืžื” ื”ื—ื•ืžืจ ื”ืืคืœ ืขืฉื•ื™ ืœื”ื™ื•ืช,
10:29
that these experiments would have seen.
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ืฉื”ื ื™ืกื•ื™ื™ื ื”ืœืœื• ื”ื™ื• ืžืจืื™ื.
10:31
And they didn't see them yet,
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ื•ื”ื ืœื ื”ืจืื• ืื•ืชื ืขื“ื™ื™ืŸ,
10:32
so we have to keep looking and thinking harder.
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ืื– ืขืœื™ื ื• ืœื”ืžืฉื™ืš ืœื—ืคืฉ ื•ืœื—ืฉื•ื‘ ื˜ื•ื‘ ื™ื•ืชืจ.
10:37
Now, another way to get a clue to what dark matter is
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ื“ืจืš ื ื•ืกืคืช ืœืงื‘ืœ ืจืžื– ืขืœ ืžื”ื• ื—ื•ืžืจ ืืคืœ,
10:42
is to study galaxies.
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ื”ื•ื ืœื™ืžื•ื“ ื’ืœืืงืกื™ื•ืช.
10:44
We already talked about
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ื›ื‘ืจ ื“ื‘ืจื ื• ืขืœ ื›ืš,
10:46
how our galaxy and many other galaxies wouldn't even be here
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ืฉื”ื’ืœืงืกื™ื” ืฉืœื ื• ื•ืจื‘ื•ืช ืื—ืจื•ืช ืืคื™ืœื• ืœื ื”ื™ื• ืคื”,
10:49
without dark matter.
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ื‘ืœื™ ื”ื—ื•ืžืจ ื”ืืคืœ.
10:51
Those models also make predictions
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ื”ืžื•ื“ืœื™ื ื”ืœืœื• ื—ื•ื–ื™ื ื’ื ื›ืŸ
10:53
for many other things about galaxies:
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ื“ื‘ืจื™ื ืจื‘ื™ื ืื—ืจื™ื ืขืœ ื’ืœืืงืกื™ื•ืช:
10:55
How they're distributed in the universe,
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ืื™ืš ื”ืŸ ืžื•ืคืฆื•ืช ื‘ื™ืงื•ื,
10:57
how they move,
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ืื™ืš ื”ืŸ ื–ื–ื•ืช,
10:59
how they evolve over time.
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ืื™ืš ื”ืŸ ืžืชืคืชื—ื•ืช ืขื ื”ื–ืžืŸ.
11:01
And we can test those predictions with observations of the sky.
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ื•ืื ื• ื™ื›ื•ืœื™ื ืœื‘ื—ื•ืŸ ืืช ื”ืชื—ื–ื™ื•ืช ื”ืœืœื• ื‘ืืžืฆืขื•ืช ืชืฆืคื™ื•ืช ืฉืœ ื”ืฉืžื™ื.
11:06
So let me just give you two examples
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ืื ื™ ืืชืŸ ืœื›ื ืฉืชื™ ื“ื•ื’ืžืื•ืช
11:08
of these kinds of measurements we can make with galaxies.
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ืœืกื•ื’ ื”ื–ื” ืฉืœ ืžื“ื™ื“ื•ืช ืฉืื ื• ื™ื›ื•ืœื™ื ืœื‘ืฆืข ืขื ื’ืœืงืกื™ื•ืช.
11:13
The first is that we can make maps of the universe with galaxies.
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ื”ืจืืฉื•ื ื” ื”ื™ื ืฉืื ื• ื™ื›ื•ืœื™ื ืœืžืคื•ืช ืืช ื”ื™ืงื•ื ืขื ื’ืœืงืกื™ื•ืช.
11:18
I am part of a survey called the Dark Energy Survey,
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ืื ื™ ื—ืœืง ืžื—ืงืจ ื”ื ืงืจื ื—ืงืจ ื”ื—ื•ืžืจ ื”ืืคืœ,
11:20
which has made the largest map of the universe so far.
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ืฉื™ื™ืฆืจ ืืช ืžืคืช ื”ื™ืงื•ื ื”ื’ื“ื•ืœื” ื‘ื™ื•ืชืจ ืขื“ ื›ื”.
11:25
We measured the positions and shapes of 100 million galaxies
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ืžื“ื“ื ื• ืืช ืžื™ืงื•ืžืŸ ื•ืฆื•ืจืชืŸ ืฉืœ 100 ืžื™ืœื™ื•ืŸ ื’ืœืงืกื™ื•ืช,
11:30
over one-eighth of the sky.
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ื™ื•ืชืจ ืžืฉืžื™ื ื™ืช ื”ืฉืžื™ื™ื.
11:34
And this map is showing us all the matter in this region of the sky,
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ื•ื”ืžืคื” ื”ื–ื• ืžืจืื” ืœื ื• ืืช ื›ืœ ื”ื—ื•ืžืจ, ื”ืงื™ื™ื ื‘ืื–ื•ืจ ื”ื–ื” ืฉืœ ื”ืฉืžื™ื™ื,
11:39
which is inferred by the light distorted from these 100 million galaxies.
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ืฉื ื™ืชืŸ ืœื”ืฆื‘ื™ืข ืขืœื™ื• ื‘ื’ืœืœ ื”ืื•ืจ ื”ืžืชืขื•ื•ืช ืžืื•ืชืŸ 100 ืžื™ืœื™ื•ืŸ ื’ืœืงืกื™ื•ืช.
11:46
The light distorted from all of the matter
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ื”ืื•ืจ ื”ื–ื” ืžืชืขืงืœ ืžื›ืœ ื”ื—ื•ืžืจ ื”ื–ื”
11:49
that was between those galaxies and us.
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ืฉื ืžืฆื ื‘ื™ื ื™ื ื• ืœื‘ื™ืŸ ื”ื’ืœืงืกื™ื•ืช ื”ืืœื”.
11:54
The gravity of the matter is strong enough to bend the path of light.
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ื›ื•ื— ื”ืžืฉื™ื›ื” ืฉืœ ื”ื—ื•ืžืจ ื”ื–ื” ื’ื“ื•ืœ ืžืกืคื™ืง ื‘ืฉื‘ื™ืœ ืœืขืงื ืืช ื”ืฉื‘ื™ืœ ืฉืœ ื”ืื•ืจ.
11:59
And it gives us this image.
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ื•ืžืชืงื‘ืœืช ื”ืชืžื•ื ื” ื”ื–ื•.
12:04
So these kinds of maps
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ืžืคื•ืช ืžืกื•ื’ ื–ื”
12:05
can tell us about how much dark matter there is,
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ื™ื›ื•ืœื•ืช ืœื•ืžืจ ืœื ื• ื›ืžื” ื—ื•ืžืจ ืืคืœ ื™ืฉื ื•,
12:08
they also tell us where it is
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ื”ืŸ ื’ื ืื•ืžืจื•ืช ืœื ื• ื”ื™ื›ืŸ ื”ื•ื ื ืžืฆื
12:11
and how it changes over time.
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ื•ืื™ืš ื”ื•ื ืžืฉืชื ื” ืœืื•ืจืš ื–ืžืŸ.
12:14
So we're trying to learn about what the universe is made of
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ืื– ืื ื• ืžื ืกื™ื ืœืœืžื•ื“ ืžืžื” ื”ื™ืงื•ื ืขืฉื•ื™,
12:18
on the very largest scales.
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ื‘ืกื“ืจื™ ื’ื•ื“ืœ ื”ื’ื“ื•ืœื™ื ื‘ื™ื•ืชืจ.
12:21
It turns out that the tiniest galaxies in the universe
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ืžืชื‘ืจืจ, ื›ื™ ื”ื’ืœืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื‘ื™ื•ืชืจ ื‘ื™ืงื•ื,
12:25
provide some of the best clues.
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ืžืกืคืงื•ืช ื—ืœืง ืžื”ืจืžื–ื™ื ื”ื˜ื•ื‘ื™ื ื‘ื™ื•ืชืจ.
12:29
So why is that?
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ืžื“ื•ืข ื–ื” ื›ืš?
12:31
Here are two example simulated universes
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ื”ื ื” ืฉืชื™ ื“ื•ื’ืžืื•ืช ืฉืœ ื™ืงื•ืžื™ื ืžืžื•ื“ืœื™ื
12:34
with two different kinds of dark matter.
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ืขื ืฉื ื™ ืกื•ื’ื™ื ืฉื•ื ื™ื ืฉืœ ื—ื•ืžืจ ืืคืœ.
12:37
Both of these pictures are showing you a region
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ืฉืชื™ ื”ืชืžื•ื ื•ืช ืžืฆื™ื’ื•ืช ืื™ื–ื•ืจ
12:39
around a galaxy like the Milky Way.
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ืกื‘ื™ื‘ ื’ืœืงืกื™ื” ื›ืžื• ืฉื‘ื™ืœ ื”ื—ืœื‘.
12:42
And you can see that there's a lot of other material around it,
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ื•ืืชื ื™ื›ื•ืœื™ื ืœืจืื•ืช ืฉื™ืฉ ื”ืจื‘ื” ื—ื•ืžืจ ืื—ืจ ืกื‘ื™ื‘ื”,
12:45
little small clumps.
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ื”ืฆื˜ื‘ืจื•ื™ื•ืช ืงื˜ื ื•ืช.
12:47
Now, in the image on the right,
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ืขื›ืฉื™ื•, ื‘ืชืžื•ื ื” ืฉืžื™ืžื™ืŸ,
12:49
dark matter particles are moving slower than they are in the one on the left.
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ื—ืœืงื™ืงื™ ื”ื—ื•ืžืจ ื”ืืคืœ ื ืขื™ื ืœืื˜ ื™ื•ืชืจ ืžื”ื—ืœืงื™ืงื™ื ื‘ืชืžื•ื ื” ืžืฉืžืืœ.
12:54
If those dark matter particles are moving really fast,
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ืื ืื•ืชื ื—ืœืงื™ืงื™ ื—ื•ืžืจ ืืคืœ ื ืขื™ื ืžืžืฉ ืžื”ืจ,
12:57
then the gravity in small clumps is not strong enough
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ืื–ื™ ื›ื•ื— ื”ื›ื‘ื™ื“ื” ื‘ื”ืฆื˜ื‘ืจื•ื™ื•ืช ืงื˜ื ื•ืช ืื™ื ื• ื—ื–ืง ืžืกืคื™ืง
13:00
to slow those fast particles down.
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ืขืœ ืžื ืช ืœื”ืื˜ ืืช ื”ื—ืœืงื™ืงื™ื ื”ืžื”ื™ืจื™ื.
13:03
And they keep going.
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ื•ื”ื ืžืžืฉื™ื›ื™ื ืœื ื•ืข.
13:04
They never collapse into these small clumps.
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ื”ื ืœืขื•ืœื ืœื ืงื•ืจืกื™ื ืืœ ืชื•ืš ื”ื”ืฆื˜ื‘ืจื•ื™ื•ืช ื”ืงื˜ื ื•ืช.
13:06
So you end up with fewer of them than in the universe on the right.
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ืื– ืœื‘ืกื•ืฃ ื™ืฉื ืŸ ืคื—ื•ืช ื ืงื•ื“ื•ืช ื›ืืœื”, ืžืืฉืจ ื‘ื™ืงื•ื ืžื™ืžื™ืŸ.
13:11
If you don't have those small clumps,
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ืื ืื™ืŸ ื”ืฆื˜ื‘ืจื•ื™ื•ืช ืงื˜ื ื•ืช,
13:13
then you get fewer small galaxies.
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ืžืชืงื‘ืœื•ืช ืคื—ื•ืช ื’ืœืงืกื™ื•ืช ืงื˜ื ื•ืช.
13:18
If you look up at the southern sky,
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ืื ืชื‘ื™ื˜ื• ืžืขืœื” ืืœ ื”ืฉืžื™ื™ื ื”ื“ืจื•ืžื™ื™ื,
13:19
you can actually see two of these small galaxies,
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ื ื™ืชืŸ ืœืžืขืฉื” ืœืจืื•ืช ืฉืชื™ื™ื ืžื”ื’ืœืืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื”ืืœื”,
13:23
the largest of the small galaxies that are orbiting our Milky Way,
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ื”ื’ื“ื•ืœื•ืช ื‘ื™ื•ืชืจ ืžื‘ื™ืŸ ื”ื’ืœืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื”ืกื•ื‘ื‘ื•ืช ืืช ืฉื‘ื™ืœ ื”ื—ืœื‘ ืฉืœื ื•,
13:26
the Large Magellanic Cloud and the Small Magellanic Cloud.
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ืขื ืŸ ืžื’ืœืŸ ื”ื’ื“ื•ืœ ื•ืขื ืŸ ืžื’ืœืŸ ื”ืงื˜ืŸ.
13:30
In the last several years,
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ื‘ืฉื ื™ื ื”ืื—ืจื•ื ื•ืช,
13:32
we have detected a whole bunch more even smaller galaxies.
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ื’ื™ืœื™ื ื• ื”ืžื•ืŸ ื’ืœืงืกื™ื•ืช, ืงื˜ื ื•ืช ืืฃ ื™ื•ืชืจ.
13:35
This is an example of one of them
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ื–ื• ื“ื•ื’ืžื” ืœืื—ืช ืžื”ืŸ,
13:37
that we detected with the same dark energy survey
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ืฉื’ื™ืœื™ื ื• ื‘ืืžืฆืขื•ืช ืื•ืชื• ืžื—ืงืจ ื—ื•ืžืจ ืืคืœ,
13:40
that we used to make maps of the universe.
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ื‘ื• ื”ืฉืชืžืฉื ื• ื›ื“ื™ ืœื™ืฆื•ืจ ืžืคื•ืช ืฉืœ ื”ื™ืงื•ื.
13:43
These really small galaxies,
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ื”ื’ืœืงืกื™ื•ืช ื”ืงื˜ื ื˜ื ื•ืช ื”ืืœื”,
13:45
some of them are extremely small.
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ื—ืœืงืŸ ืงื˜ื ื•ืช ืžืื•ื“.
13:48
Some of them have as few as a few hundred stars,
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ืœื—ืœืงืŸ ื™ืฉ ืจืง ื›ืžื” ืžืื•ืช ื›ื•ื›ื‘ื™ื,
13:51
compared to the few hundred billion stars in our Milky Way.
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ื‘ื”ืฉื•ื•ืื” ืœื›ืžื” ืžืื•ืช ืžื™ืœื™ืืจื“ื™ ื›ื•ื›ื‘ื™ื ื‘ืฉื‘ื™ืœ ื”ื—ืœื‘ ืฉืœื ื•.
13:55
So that makes them really hard to find.
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ืื– ื–ื” ื”ื•ืคืš ืื•ืชืŸ ืœืงืฉื•ืช ืžืื•ื“ ืœื’ื™ืœื•ื™.
13:57
But in the last decade,
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ืืš ื‘ืขืฉื•ืจ ื”ืื—ืจื•ืŸ,
13:59
we've actually found a whole bunch more of these.
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ืžืฆืื ื• ืžืงื‘ืฅ ืฉืœื ืฉืœื”ืŸ.
14:02
We now know of 60 of these tiny galaxies
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ืื ื• ืขื›ืฉื™ื• ืžื›ื™ืจื™ื ื› 60 ืžื”ื’ืœืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื”ืืœื”,
14:05
that are orbiting our own Milky Way.
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ืฉื—ื’ื•ืช ืกื‘ื™ื‘ ืฉื‘ื™ืœ ื”ื—ืœื‘ ืฉืœื ื•.
14:08
And these little guys are a big clue to dark matter.
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ื•ื”ื—ื‘ืจ'ื” ื”ืงื˜ื ื™ื ื”ืœืœื• ื”ื ืจืžื–ื™ื ื’ื“ื•ืœื™ื ืœื—ื•ืžืจ ืืคืœ.
14:12
Because just the existence of these galaxies tells us
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ืžื›ื™ื•ื•ืŸ ืฉืจืง ื”ืงื™ื•ื ืฉืœ ื”ื’ืœืงืกื™ื•ืช ื”ืืœื” ืžืกืคืจ ืœื ื•,
14:16
that dark matter can't be moving very fast,
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ืฉื”ื—ื•ืžืจ ื”ืืคืœ ืœื ื ืข ืžืื•ื“ ืžื”ืจ,
14:19
and not much can be happening when it runs into normal matter.
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ื•ืœื ื”ืจื‘ื” ืงื•ืจื” ื›ืืฉืจ ื”ื•ื ืคื•ื’ืฉ ื‘ื—ื•ืžืจ ืจื’ื™ืœ.
14:24
In the next several years,
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ื‘ื›ืžื” ืฉื ื™ื ื”ื‘ืื•ืช,
14:26
we're going to make much more precise maps of the sky.
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ืื ื• ืขื•ืžื“ื™ื ืœื™ืฆื•ืจ ืžืคื•ืช ืžื“ื•ื™ื™ืงื•ืช ื”ืจื‘ื” ื™ื•ืชืจ ืฉืœ ื”ืฉืžื™ื™ื.
14:31
And those will help refine our movies
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ื•ื”ืŸ ื™ืขื–ืจื• ืœื ื• ืœืœื˜ืฉ ืืช ื”ืกืจื˜ื™ื ืฉืœื ื•,
14:33
of the whole universe and the entire galaxy.
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ืฉืœ ื›ืœ ื”ื™ืงื•ื ื•ื”ื’ืœืงืกื™ื”.
14:37
Physicists are also making new, more sensitive experiments
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ืคื™ื–ื™ืงืื™ื ืขื•ืจื›ื™ื ื‘ื ื•ืกืฃ ื’ื ื ื™ืกื•ื™ื™ื ื—ื“ืฉื™ื, ืจื’ื™ืฉื™ื ื™ื•ืชืจ,
14:41
to try to catch some sign of dark matter in their laboratories.
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ื›ื“ื™ ืœื ืกื•ืช ืœืชืคื•ืก, ืกื™ืžืŸ ื›ืœืฉื”ื• ืœื—ื•ืžืจ ืืคืœ, ื‘ืžืขื‘ื“ื•ืช ืฉืœื”ื.
14:47
Dark matter is still a huge mystery.
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ื—ื•ืžืจ ืืคืœ ืขื•ื“ื ื• ืชืขืœื•ืžื” ื’ื“ื•ืœื”.
14:50
But it's a really exciting time to be working on it.
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ืื‘ืœ ื–ื”ื• ื–ืžืŸ ืžืจื’ืฉ ืžืื•ื“ ืœืขื‘ื•ื“ ืขืœื™ื”.
14:54
We have really clear evidence it exists.
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ื™ืฉ ืœื ื• ื”ื•ื›ื—ื•ืช ื‘ืจื•ืจื•ืช ืœืงื™ื•ืžื•.
14:57
From the scale of the smallest galaxies
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ืžื’ื•ื“ืœืŸ ืฉืœ ื”ื’ืœืงืกื™ื•ืช ื”ืงื˜ื ื•ืช ื‘ื™ื•ืชืจ,
14:59
to the scale of the whole universe.
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ืœืงื ื” ื”ืžื™ื“ื” ืฉืœ ื”ื™ืงื•ื ื›ื•ืœื•.
15:03
Will we actually find it and figure out what it is?
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ื”ืื ื‘ืืžืช ื ืžืฆื ืื•ืชื• ื•ื ื’ืœื” ืžื” ื”ื•ื?
15:08
I have no idea.
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ืื™ืŸ ืœื™ ืžื•ืฉื’.
15:10
But it's going to be a lot of fun to find out.
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ืื‘ืœ ื–ื” ื”ื•ืœืš ืœื”ื™ื•ืช ืžืื•ื“ ื›ื™ืฃ ืœื’ืœื•ืช.
15:13
We have a lot of possibilities for discovery,
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ื™ืฉ ืœื ื• ื”ืžื•ืŸ ืืคืฉืจื•ื™ื•ืช ืœื’ื™ืœื•ื™,
15:15
and we definitely will learn more about what it is doing
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ื•ืื ื• ื‘ื•ื•ื“ืื•ืช ื ืœืžื“ ื™ื•ืชืจ ืขืœื™ื• ื•ืขืœ ืžื” ืฉื”ื•ื ืขื•ืฉื”
15:19
and about what it isn't.
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ื•ืขืœ ืžื” ืฉื”ื•ื ืื™ื ื•.
15:21
Regardless of whether we find that particle anytime soon,
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ืœืœื ืงืฉืจ ืœืื ื ืžืฆื ืืช ื”ื—ืœืงื™ืง ื”ื–ื” ื‘ืงืจื•ื‘,
15:24
I hope I have convinced you
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ืื ื™ ืžืงื•ื•ื” ืฉืฉื›ื ืขืชื™ ืืชื›ื
15:26
that this mystery is actually really close to home.
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ืฉื”ืชืขืœื•ืžื” ื”ื–ื• ืœืžืขืฉื” ืžืื•ื“ ืงืจื•ื‘ื” ืืœื™ื ื•.
15:30
The search for dark matter
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ื”ื—ื™ืคื•ืฉ ืื—ืจ ื—ื•ืžืจ ืืคืœ
15:32
may just be the key to a whole new understanding of physics
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ืขืฉื•ื™ ืœื”ื™ื•ืช ื”ืžืคืชื— ืœื”ื‘ื ื” ื—ื“ืฉื” ืœื’ืžืจื™ ืฉืœ ืคื™ื–ื™ืงื”
15:35
and our place in the universe.
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ื•ืžืงื•ืžื ื• ื‘ื™ืงื•ื.
15:37
Thank you.
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ืชื•ื“ื”-ืจื‘ื”.
15:38
(Applause)
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(ืžื—ื™ืื•ืช ื›ืคื™ื™ื)
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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