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  • [♩INTRO]

  • Even though they, and nobody else, will be around to see it,

  • scientists are fascinated by the end of the universe.

  • It's kind of like the Big Bangthere's just something so interesting about

  • knowing where your atoms came from,

  • and where they're ultimately going to go in billions of years.

  • Right now, there are a few ideas about how everything could end,

  • but many researchers seem to agree on what's called the Big Freeze

  • (which we used to call heat death, but we've now rebranded)

  • where everything is spread so thin that activity basically stops.

  • Except, based on the results from a paper published last week

  • in Nature Astronomy, that might not actually be true.

  • Instead, there's a chance that everything in existence will eventually be ripped apart.

  • And it would all be thanks to dark energy.

  • If dark energy sounds like kind of a fuzzy concept, you are correct!

  • Scientists think it makes up about 70% of the stuff in the universe,

  • and that it's the reason the expansion of the universe is accelerating.

  • But there's a lot they're still figuring out.

  • Some of their research into dark energy has involved tools called standard candles.

  • Standard candles are objects or events of known brightness

  • that are used to measure distance in the far-off universe.

  • Essentially, if you know how bright something should be up close,

  • then how bright it actually looks indicates how far away it is.

  • For decades, the most important standard candle

  • has been a special kind of exploding star called a type Ia supernova.

  • These events always have the same brightness, and in the 1990s, they allowed

  • scientists to discover that the universe's rate of expansion was accelerating.

  • But what's really important for this recent study is that all the estimates

  • provided by type Ia supernovas also indicate

  • that the density of dark energy is fixed.

  • There's a lot of math involved,

  • but this fact is a big reason they believe the Big Freeze is most likely.

  • The problem is, you can only see so far with any given candle before

  • it gets too dim, and type Ias can't take us back to the beginning of the universe.

  • Because light can only move so fast,

  • looking deep into space is like looking back in time.

  • And these supernovas only allow us to see what things were like

  • 4.5 billion years or so after the Big Bang.

  • Admittedly, there are some data sources,

  • like one called the Cosmic Microwave Background,

  • that can tell us what things were like around 400 thousand years after the Big Bang.

  • But that Background actually seems to disagree

  • with what supernovas say about the expansion rate,

  • which has had astronomers debating different options for years.

  • There's also been a 4-billion-year gap between the two data sources,

  • so it's been hard to figure out what's going on.

  • That's where last week's news comes in.

  • In their paper, a pair of astronomers proposed a new kind of standard candle,

  • one that can let us peer back to that sweet spot

  • just 1-2 billion years after the Big Bang.

  • Their idea relies on quasars,

  • rapidly-growing black holes that are among the universe's brightest objects.

  • Although quasars vary a lot in brightness, the authors claim that the ratio of

  • ultraviolet brightness to X-ray brightness is not only more predictable,

  • but reliable enough to indicate a quasar's distance.

  • They point out that, at distances where both type Ia supernovas

  • and quasars are visible, they provide comparable results, too.

  • But the key is, farther from Earth, and further back in time, only quasars are visible.

  • And after looking at some of those super-distant objects, the authors claim to

  • have made a surprising observation: In the first couple billion years after the

  • Big Bang, the growth rate of the universe didn't match the predictions

  • made by the supernova-based models.

  • Back then, things seemed to be getting bigger more slowly than expected.

  • That implies that the amount of dark energy

  • driving that expansion hasn't been constant after all.

  • Instead, it's been increasing over time.

  • It sounds like a wild idea, but it would help explain

  • why there isn't a perfect match between the expansion rate

  • we see from supernovas and that Cosmic Microwave Background.

  • So it's not like there's no foundation for it.

  • Still, before they rewrite your Astronomy textbook and make you buy a brand

  • new one for $400, it's important to remember two things.

  • One, these results will need a lot of confirmation

  • before they're accepted into the mainstream theory.

  • And two, scientists have effectively no clue what dark energy actually is,

  • so it's not even worth asking questions like what would be generating more

  • and more of it, because we don't even know what IT is.

  • But if these results are true, there is one thing we do know.

  • This would mean that, instead of ending in the Big Freeze, the universe would

  • eventually end in the so-called Big Rip, where ever-increasing dark energy

  • tears apart every particle until there's nothing left and no one to see it.

  • But the assumption is that it's not such a big deal,

  • because there is no way we would be around by then.

  • Thanks for watching this episode of SciShow Space News!

  • If your brain is feeling all discombobulated after learning about dark energy,

  • you might enjoy our episode over on SciShow Psych about how to clear your mind.

  • I know that after discussing existential questions like the end of the universe,

  • I could use that.

  • [♩OUTRO]

[♩INTRO]

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