Placeholder Image

字幕表 動画を再生する

  • SciShow Space is supported by Brilliant.org.

  • [♪ INTRO]

  • One thing that humans simply cannot stop doing

  • is trying to figure out where we came from and why we exist.

  • That's, like, Our Big Thing.

  • That, and getting really inventive with fried foods,

  • but that's a subject for another channel.

  • Philosophers and fry cooks are still working on those questions, but science can at least

  • answer one thing: when the universe began.

  • And right now, we're pretty confident that it all happened around

  • 13.8 billion years ago with the Big Bang.

  • Figuring that out hasn't been easy, and our estimates could still get better, but

  • thanks to some useful tools and a lot of math, we're off to a really good start.

  • To calculate the age of the universe, astronomers use two main tools, or pieces of evidence.

  • The first is pretty intuitive: They look for old stuff.

  • For the most part, that means looking at really faraway stuff.

  • See, the universe has been expanding ever since the Big Bang, so the very oldest objects

  • have been hurtling away from the Earth for billions of years.

  • And based on how far an object is, astronomers can get a rough idea of how old it is.

  • So far, using photos, like ones from the Hubble Space Telescope, researchers have been able

  • to find clusters of stars as old as 13.2 billion years!

  • But they don't know the stars are old just by looking at them.

  • To figure it out, they have to take into account some of the cool, weird ways that light behaves.

  • See, as the universe expands, it also stretches the light waves traveling through it.

  • So if a star is moving away from Earth, its light will be stretched and have a longer

  • wavelength by the time it gets to us.

  • This is called redshift.

  • By seeing how stretched, or redshifted, a star's light is, and doing some math, astronomers

  • can get a rough idea of how far and how old a star is.

  • But that isn't the only tool they use, because even though we can detect some faraway objects,

  • others are still really difficult to observe over those large distances.

  • Mostly, this just tells us that the universe has to be at least 13.2 billion years old.

  • To refine the estimate, astronomers also use measurements

  • about the expansion of the universe itself.

  • We've known the universe was expanding since the late 1920s, but understanding how it's

  • expanding is what's especially useful.

  • Knowing how fast it's happening and how that speed is changing

  • really allows researchers to work backwards from right now,

  • to find out exactly when the universe was a tiny seed of everything.

  • It's basically like how a forensic scientist can study an explosion site

  • and tell you when the bomb went off.

  • Just with a much bigger bomb in this case.

  • Two major discoveries have helped us understand this expansion.

  • The first was type Ia supernovas, which form from the explosion of a tiny white dwarf star

  • and some other stellar companion.

  • In 2011, a team of scientists won a Nobel prize for using them to

  • prove that the universe's expansion is getting faster.

  • These supernovas are extremely bright, and their brightnesses are all pretty uniform,

  • so one of them will look a lot like any other.

  • This makes them really good for calculating distances,

  • or what astronomers call standard candles.

  • Since we know what their brightnesses should be at any given distance, whether it's a

  • million or a billion light-years away, they're easy to use in measurements.

  • And after years of measurements, astronomers noticed that the redshifts for these supernovas

  • was a lot smaller than they should've been for galaxies so far away.

  • That means that, sometime after the supernovas emitted their light,

  • they actually got farther from Earth than expected.

  • That could could only be explained by a universe that's expanding faster as the years go

  • on, although we aren't positive what's causing that to happen.

  • But it has helped us understand when the Big Bang happened.

  • Before we knew that the expansion of the universe was accelerating,

  • our calculations about its age could be pretty inaccurate.

  • Astronomers used to assume a constant rate of expansion, so if you're working backwards

  • from our current rate, you'd get a universe that's way too young.

  • Or, if you picked a bad standard candle, you'd get inaccurate measurements, too.

  • For instance, Hubble's original calculations from the 1920s

  • used a type of star called a Cepheid variable as the standard candle,

  • and that suggested the universe was about 2 billion years old.

  • Which is definitely not right.

  • Science is a process.

  • Still, type Ia supernovas aren't the only way we've studied how the universe is expanding.

  • The other way we've figured out the rate of expansion is with the Cosmic Microwave

  • Background, or CMB, which is the energetic glow left over from the Big Bang.

  • Well, it's not wildly energetic, it comes in at 2.7 Kelvin, or about -270 degrees Celsius.

  • But it's not 2.7 Kelvin everywhere you look!

  • And that's super useful to us!

  • Those temperature variations can tell us about the movement of objects

  • and the densities of gases in the universe,

  • both of which are used in calculating the universe's rate of expansion.

  • And along with type Ia supernovas, these studies have allowed us to get a much more precise

  • picture of how the universe has been growing since it began.

  • That's let us zero in on our current age estimate: 13.8 billion years.

  • And our observations are just going to get better from here on out!

  • We think 13.8 billion is pretty solid, but don't be surprised if you hear that number

  • change a little bit as we make better observations.

  • It just means we're getting better at science.

  • And speaking of CMB, Brilliant.org has a lesson in their astronomy unit that covers even more

  • of what that background radiation has taught scientists about the universe.

  • And it's really fun, because each question makes you an active problem solver.

  • So let's see if we learned anything from everything I was just telling you about.

  • I'm going to take the quiz here in the studio, but Brilliant.org

  • also set up a link so that you can test your knowledge at home for free.

  • You can find that at brilliant.org/SciShowSpaceCosmology

  • So like all Brilliant quizzes, this one opens with giving you more information

  • about how to solve these problems.

  • This quiz kind of starts with explaining the CMB a little bit more before we dive into

  • answering questions about it, and one of the things that I love about Brilliant is that

  • it's not just text-based, that you're working with,

  • you have amazing images like this map.

  • Not only do they help me understand the problem that I'm trying to solve, but they give

  • context to everything that they're talking about in this quiz, and that helps me make

  • more sense of it, but also retain that information over the long run and be excited about it.

  • So check out the quiz for yourself, and let us know how you do in the comments below.

  • This quiz is totally free for you to play with, so have at it.

  • And the first 200 to sign up at brilliant.org/scishowspace

  • will get 20% off of their annual Premium subscription,

  • and be supporting SciShow Space, so thank you!

  • [♪ OUTRO]

SciShow Space is supported by Brilliant.org.

字幕と単語

動画の操作 ここで「動画」の調整と「字幕」の表示を設定することができます

B1 中級

宇宙の時代を知るには? (How Do We Know the Age of the Universe?)

  • 0 0
    林宜悉 に公開 2021 年 01 月 14 日
動画の中の単語