Even the universe has an end. With its incomparable size and scope,
it can feel as though this reality will just go on and on forever… but actually, according to one
model at least, there’s an extremely bizarre fate awaiting it, at the end of the line.
This is Unveiled, and today we’re answering the extraordinary question;
what if we lived in a black dwarf universe?
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We live on one of eight confirmed planets in the solar system. We orbit one star of around
100 billion stars in the Milky Way galaxy, at the lower estimate. The Milky Way is just one
average-sized galaxy among approximately 200 billion galaxies in the universe as a whole,
according to NASA figures. The universe is 13.8 billion years old,
and the observable part of it is 93 billion lightyears across. The unobservable universe
is potentially infinite in nature. The entire thing is expanding at an accelerating rate,
as well, devouring the seeming nothingness beyond. And yet it can (and probably will) die.
The ultimate fate of the universe is a question that humankind has wrestled with for centuries,
but never more so than in the last few decades. The list of potential scenarios is by now well
known. It could be that our expanding universe hits reverse, and everything ends in a Big Crunch.
It could be that expansion continues until it can continue no more, in the Big Rip. Or that
the total energy within the universe eventually fritters away completely, in a Big Freeze.
With all of those possibilities, though, it’s not as though we’re ever here today
gone tomorrow. If humans were around at the end of all things - which is laughably unlikely,
but still - then it will be a very gradual grinding to a halt,
over billions or even trillions of years. There are some scenarios where this wouldn’t be the
case - such as should this universe actually be just the plaything of a higher power,
who then just decides to switch it off. That would be instant. But it’s also not an “end of
the universe” theory that ranks especially highly (at present) in terms of what’s most likely.
Current science predicts a long and slow death, no matter which route the universe ends up taking.
For today’s video, though, we’re imagining that the Big Crunch isn’t what will happen. Instead,
we’re in a reality where we’re headed either for the Big Rip or Freeze. The universe doesn’t
rebound and retract, it just continues expanding… and the mechanics of it carry on mostly unchanged.
To understand what will happen next, in general, we can first look at our own sun.
The sun has been happily burning for around 4.6 billion years now, and very early in its life the
rest of the solar system formed around it. The inner, rocky planets; the outer, gaseous worlds;
the countless asteroids and endless cosmic dust. But we know that the sun, in its current form,
has likely already passed the midway point in its life. In about 4 billion years’ time,
it’s expected to go red giant. To rush outwards as part of a ruthless,
fiery expansion that will totally reshape its surrounding area - including the Earth,
which might even find itself devoured completely.
But, while the transition to the red giant stage will be a momentous time for the sun,
its story doesn’t finish there. It’s sometimes shown as though the red giant will be some kind
of final explosion for our star… but, really, it’s the sun reinventing itself. In turning into a red
giant, the sun’s fusion of hydrogen into helium stops. For a while, it will fuse helium into
carbon instead, as it enters into a whole new era. Around half of the sun’s mass will then be lost,
blasted out into space… but the other half will remain as a white dwarf. A scorching
ball of spectacular density, about the same size as Earth is now, or slightly larger.
From here, it’s a long time until the sun’s next major change. In its white dwarf form
it’ll simply be cooling down… but, such is the immense energy contained within it,
that cooling down process will take literally a quadrillion years, at least. Many, many times
longer than the total age of the universe so far. When it has cooled to almost absolute zero,
though, it will no longer be emitting visible light. It’ll no longer be producing anything
much in terms of energy, and will be left as an impeccably dark mass suspended in space. Now,
our sun, the star that once provided all we need to live,
has truly reached the end of its timeline and has become a black dwarf.
At present, a black dwarf is a hypothetical star type, seeing as there hasn’t yet been enough time
in the universe for any of them to form. However, scientists do believe that this is the ultimate
fate for many low mass stars, like our sun. For more massive stars there are other endgames
available, including collapsing into a black hole or a neutron star. But for smaller stellar masses,
those fates aren’t possible. When they reach black dwarf, they’re classified as remnants of
what they once were. The power within them has petered out, although they might well
still exist until the end of the universe itself - via the Big Rip or Big Freeze.
So, what would happen if we lived in a black dwarf universe? Essentially,
nothing much. Imagine that you had a working time machine shooting as far forward in time
as it’s possible to go - trillions upon trillions of years later than now - you could well arrive
at a moment when black dwarfs and black holes are all there is. Only, thanks to expansion, none of
these essentially invisible objects are even close together any more. Millions of lightyears separate
one stellar husk from the next; the planets that once swirled around them are long gone;
the chemical makeup of the universe has broken down; and the prospects for life are almost
certainly zero. More than any other doomsday scenario, this really is the end of all things.
That is, unless life has found a way. Again, what we’re picturing here is a time so far removed
from right now that really it’s impossible to comprehend. Modern humans are only a few hundred
thousand years old, and have only been around for a tiny fraction of the Earth’s (and the sun’s)
total lifetime. Meanwhile, the Earth and the Sun have only been here for around a third of the
time that the universe itself has. But even all of that… everything that has happened so far… fades
into miniscule insignificance compared to anything that makes it to the black dwarf age. If life has
survived - and that’s probably one of the biggest ifs we’ve ever contemplated on this channel - then
it must surely mean one of two things. Either life has transcended to a wholly non-physical form,
and no longer relies upon the universe to host it… or life has cracked open the multiverse,
and so can view this universe’s fate as if from another dimension.
What’s your verdict? Could life survive to see space (as we know it) marked only by cold and
drained black dwarfs? Or is this a jump into the future that nothing else can take? It’s
certainly one of the bleaker possibilities for how all of this could end. The sun as we know it,
as we’ve always known it, seems as though it should be eternal. An unbeatable, undiminishing
power source. But the sad truth is that it isn’t… and that even it will one day fade out forever.
Between now and then - and a seemingly much more pressing concern for Earth,
at least - is the red giant that the sun will balloon into in about four billion years’ time.
For life on Earth, this means that our planet will actually become too
hot to live on in only around one billion years’ time. Our days are already numbered;
our planet is already locked in for a huge challenge that lies ahead.
But, while it can feel as though the coming red giant should really be all there is to
worry about, there’s sure to arrive a day when even that’s long forgotten. As we are,
it can be easy to forget just how fleeting our own existences will ultimately prove to be. Not
only individually, nor even as a species, but as a world. Because, while we might never see quite so
far into the future ourselves… that’s what would happen if we lived in a black dwarf universe.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
clips from Unveiled, and make sure you subscribe and ring the bell for our latest content.