[♩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 Bang — there'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]