There is a theory which states that if ever
anyone discovers exactly what the Universe is for and why it is here, it will instantly
disappear and be replaced by something even more bizarre and inexplicable So today we will be looking at a number of
the models predicting the eventual fate of the Universe. As you can imagine this is fairly complex
topic so we will be joined today Dr. Paul M. Sutter, an Astrophysicist with Ohio State
University. It is also quite a long topic so this will
be a two part episode, and you can watch part 2 over on Paul’s channel, which also an
excellent place to visit to learn more about cosmology in general. To discuss the End of the Universe we might
as well start with the beginning, both where it came from and how human thought on this
matter has evolved as we learned more. The Big Bang theory was proposed almost a
century ago and has solidified its status since then, but people have been thinking
about the origin of the Universe for at least as long as we have had recorded history. They obviously didn’t have the same resources
we have nowadays but typically drew three basic conclusions that remained popular up
to modern times. Since the world around them could be seen
to change on a daily basis, but not necessarily all that much or significantly, they tended
to conclude either the Universe at one point did not exist, or it has always existed and
changes are cyclical, like the sunrise or turning of seasons, or that at the grand scale
it pretty much doesn’t change at all. Which is to say, snow may fall or melt on
a mountain, trees might grow on it and die, but the mountain is unchanged and so is the
world it sits on. It’s easy for us to look back to antiquity
and how little they knew about science and dismiss their thoughts on this topic, but
it still lays out the conversation we’ve had in more modern times and are still discussing. If the Universe began, then how did that happen,
who acted or what occurred to make that happen, and what came before? If there was something before, was it like
now and are we just repeating things in an endless cycle like the seasons? And if it has always been around, how is it
getting renewed? Because you can look at a forest on a mountain
changing and say it changes but the mountain does not, but eventually you’ll notice that
mountains get eroded. Rain comes down and washes dirt away, and
while you can see water evaporate and rise into clouds, you can also see rocks tumble
down a mountain but never float back up. Talking about how things began inevitably
leads to asking how they will end. Will everything just keep being renewed constantly
or reset in some cycles or just wear down one day? Needless to say folks had a lot of notions
for how things would begin and end, and they did tend to fit into one of those three options
even if the specific theory was that Earth was a disc riding around on the back of turtle
shell or elephants. With the emergence of formal logic and philosophy
we got quite a few appearing. Aristotle suggested that the Universe was
finite in size, centered on Earth, but infinite in time. This geocentric model would later be refined
by Ptolemy and stick around till Copernicus, though even in Aristotle’s time a heliocentric
model had emerged from Aristarchus, and interestingly Archimedes had calculated the Universe to
be a light year in radius. It is of course far larger than that, but
it’s worth remembering how shockingly huge that is. Archimedes had no idea what speed light traveled
at, but he knew how big that distance he’d calculated was and it meant he thought the
Universe was a billion times wider than the planet and contained a billion, billion, billion
times the volume. We now know it’s at least several billion
times wider than even that but it meant even then they’d come to realize just how tiny
Earth was, even if they gave it center stage. This doesn’t get covered much but it should
be, as Archimedes calculation of this in his paper “The Sand Reckoner” is considered
to be the first research-expository paper, and actually used Aristarchus heliocentric
model. We knew the Sun moved in the sky, as did the
planets, that’s the origin of their name as planet means wanderer. We also had discovered the concept of parallax
by then and the stars didn’t seem to experience it. Indeed it would be 2000 years before Friedrich
Bessel first successfully measured the parallax of a star in 1838. Archimedes, Aristotle, Ptolemy and Aristarchus
were all wrong of course, but Copernicus wasn’t actually right, and indeed since we can see
equally far in all directions, the Observable Universe is actually centered on Earth and
geocentric...but that’s a fairly irrelevant status. Every observer is centered in their observable
bubble. We don’t want to get in the habit of thinking
though that Copernicus was smart and right and arguing that his predecessors and opponents
were stupid and wrong, rather they were quite smart too and Copernicus was just less wrong. As we go through these theories, which each
radically alter how we viewed the Universe as we got some new piece of evidence, only
to be replaced sometime later as we got new Evidence, we do not want to view the advocates
of the previous theories as drooling morons arguing against the clear illuminating light
of reason and evidence. So prior to Copernicus the main theory was
the Universe was infinite in age, or if not had been created at some point more or less
as it was now and would continue on as it was, but also finite if huge in size (although
nowhere as big as we currently understand it). Over the next century his modified form of
this started catching on but took a hit when Newton’s Law of Universal Gravity both cemented
the heliocentric model - providing a mechanism to explain the motion of the planets - but
also kind of killed it. If every body in the universe exerts gravity
on each other, then they ought to fall together over time, and needless to say if the Universe
was infinitely old there’s been more than time enough for that. So from Newton’s work we were faced with
four possible solutions. First, the Universe is not infinitely old
and appeared at some point all spread out and is falling in. This gives us a potential Fate of the Universe,
backwards of the Big Bang, that it began huge and will end when everything eventually slams
together. Second, that gravity is not an entirely inverse-square
force, but gets even weaker at great distances, so that we are not pulling on those stars. Indeed this option has remained a common theory
until modern times and we see it in something called MOND, Modified Newtonian Dynamics,
one of the popular explanations for Dark Matter until very recently. If gravity basically just ceases at some distance,
then you don’t have to worry about stars falling together. Third, that something is holding those stars
from falling together, resisting gravity. Akin to the old notion of angels holding them
on a celestial sphere, this was never too popular, and amusingly the discovery of Dark
Energy pushing the Universe apart makes this the only one of the four interpretations to
still have some validity nowadays. And fourth, that the Universe is infinite
in both age and size, or at least size. 16th century mathematician and astronomer
Thomas Digges first suggested this one, that the stars were not at a fixed distance on
a shell but spread out over varying distances all the way out to infinity, what is now called
the Static Universe Model. He also first noted the Dark Night Sky Paradox,
later known as Olber’s Paradox even though Olber wouldn't be born for a couple more centuries. If everything is spread out over an infinite
volume, then nothing is moving because there’s always more stuff in the opposite direction
pulling it that way too. This one gained a lot of traction and its
main flaw was the aforementioned Olber’s Paradox, which points out that in an infinite
Universe any specific direction you look will eventually be obstructed by a star, so the
night sky shouldn’t be black with a few lights twinkling in it, but a uniform shade
of light, we’d be surrounded by stars and feel like we lived inside a massive sun. Indeed, were that the case everybody should
be burned to death, and if the Universe were not infinitely old, as Roemer discovered light
needed time to travel and its approximate speed in 1676. So we could predict the eventual doom of the
Universe would be the sky getting brighter and brighter as ever more distant light arrived
until we eventually burned to death. Each of these perspectives had a lot going
for and against it, in the 17th century and onto the 18th. As we move into the 19th century though we
had a few new developments. We had begun to assume stars were not all
fixed on some sphere and that Earth did orbit the Sun, so we could use that movement to
engage in some very wide parallax measurements. As mentioned, Bessel managed to get the first
measurement of distance to a star, 61 Cygni, in 1838 and two of his contemporaries, Struve
and Henderson, managed to do the same for Vega and Alpha Centauri at about the same
time. We managed to measure around a hundred more
in short order but couldn’t for many others, we can see a lot more stars than that with
the naked eye and had telescopes by now, so this inability to measure them told us they
were very far away. We had another development in this period
too, which was thermodynamics. Energy is conserved but entropy is not. We had no idea what made the stars hot yet,
but we knew they were and should be cooling down, and that if they weren’t they were
presumably being fueled someway and that fuel should be finite. We already had a lot of philosophical arguments
for why the Universe couldn’t be infinite in age, but we also had the same problems
for why it couldn’t be finite either, but thermodynamics and the speed of light piled
on to make this much harder. If the Universe is infinite in size and age,
then we should be cooked by Olber’s Paradox, and we would need to know what fueled the
stars. If the stars simply formed hot at some point
in the past, then they would eventually cool off and we’d freeze to death at the End
of the Universe instead. We were starting to get a decent idea how
old the Earth was then too. This is when we start getting the first formal
scientific theories for the beginning and ending of the Universe, as we had to wrangle
with these new issues and an increasingly large map of the Universe. Keep in mind at this point we had no idea
what powered the stars, how old any of them were or that they had different ages, or what
galaxies were. Everybody knew the problems with the Static
Universe model, the one that reasoned the Universe was infinite in size and age, but
it was sort of the default because alternatives had many problems too and none had any real
evidence. Indeed Einstein would offer up a modified
form of the Static Universe model in 1917, a decade after he unveiled Special Relativity. As mentioned many had thought the Universe
might be finite in age but infinite in size, but he went the other way and said it was
infinite in age but finite in size. This is also when we start seeing folks talk
about the universe having curvature or being flat, no surprise since relativity had started
the conversation on space and time being curved. In a traditional Euclidean Universe, two long
parallel lines stretching off to infinity will remain the same distance, like a pair
of railroads tracks. For all that they look like they’re converging
to our eyes, you can walk alongside them and see them remain the exact same distance apart. In a non-flat Universe this isn’t true,
and they might grow closer together or further apart, even though they are 100% straight. That’s not our focus yet and we didn’t
know that the Universe was expanding yet either. Now what was different that Einstein thought
the Universe would be infinite in size but not in time? There was no Hubble red shift yet to indicate
that after all. This is, incidentally, related to what Einstein
called his biggest blunder and that was the cosmological constant, a basic energy density
or pressure to space, even in total vacuum. As mentioned, if the Universe is finite in
size then gravity should yank everything together, so if it is finite in size either gravity
had to disappear after a certain distance, or the Universe couldn’t be that old and
had to start big, or something was pushing them apart. We had gotten enough at astronomy by now to
be able to see stars pulling on each other with gravity with no indication it was weakening
more than Newton said it should, so that seemed out. So if it was infinitely old something that
had to be pushing those stars apart and that was the ridiculous cosmological constant,
his fudge factor and blunder that he dismissed after Hubble expansion was found a decade
later. We had to bring it back more recently, but
will get to that later. For Einstein’s version of the Static Universe
to be true it need to explain a few things, but we only knew of one at the time he suggested
it, and that was entropy. Any model suggesting the Universe was infinitely
old, had always been and would always be, has to explain why we still have stars and
what’s replenishing their fuel. Or if not replenishing them, what was producing
the matter for new stars and what was happening to the old, cold dead ones, which should otherwise
accumulate to fill the whole Universe over infinite time. This is hardly a death blow though, since
one can assume matter eventually resets, like shuffling a deck of cards will keep further
randomizing it, increasing its entropy, but eventually return you to the original state,
resetting that entropy. And possibly new matter just appeared from
nowhere and old matter just slid into nowhere on a regular basis. Sounds a bit silly but considering the alternative
is that it all just appeared from nowhere at the same time, it’s essentially on the
same footing. It’s kind of hard to say tons of matter
can appear from nowhere at one initial moment but that it can’t do that later on nor the
reverse and just disappear. The other two flaws came later, one was intergalactic
redshift, which came up shortly after this and caused Einstein to abandon the model,
and the other was Cosmic Microwave Background Radiation, which was still about fifty years
off. Hubble didn’t discover red shift of stars,
that had already been noted, some were redshifting, indicating they were moving away, and others
were blue-shifting, indicating the reverse. What got noticed is that very distant objects,
galaxies, were almost all red-shifting and that the further off they were, the more they
were. This of course was the origin of the Big Bang
Theory, since if galaxies are all moving away, and faster the further off they were, that
would imply they used to be a lot closer. This was the exact opposite of the problem
with the Static Universe, which assumed the Universe needed to be bigger in the past if
it were not either infinite in size or had some force keeping stars from falling together. It’s big rival for quite some time was the
Steady State Model that evolved from the Static Universe version. They are not the same and folks often incorrectly
assume Steady State is the old model that the Big Bang replaced, rather the Steady State
model was proposed in 1948, a couple decades after the Big Bang Theory. In the Steady State Model we already knew
that stars formed and were fueled and died, and we could see that intergalactic red shift. So it suggest the fuel for stars is constantly
appearing in little bits and pieces, and that the Universe is indeed expanding but remains
essentially the same and has always been and will always be. That’s not as contradictory as it maybe
sounds, in a non-expanding Universe you end up with clutter of dead stars, as new matter
appears to make new stars, but if it is constantly expanding than you have new room for stuff
to be, and again the notion that single particles of hydrogen are emerging from nowhere is no
worse than new bits of space emerging from nowhere constantly, which both Big Bang and
Steady State claim happens, or that all that hydrogen emerged in one single flash of a
moment. Now you might think you’d be able to detect
new bits of matter emerging all over the place but keep in mind that our sun has several
cubic light years to itself and several billion years of life, so the 10^57 amu of mass, or
hydrogen particles, making up a new one would only require 10^40 of them emerge each second
and spread over some 10^49 cubic meters, or one appearing every second in a cubic kilometer. Needless to say spotting a single hydrogen
atom appearing in a cubic kilometer in a given second is not exactly easy to do, especially
back then. So Big Bang says all the matter appeared at
once many billions of years ago but space is constantly expanding, Steady State argues
matter is constantly appearing and so is space. There’s no problem by the way with an infinite
object expanding, twice of infinity is still infinity but it can get bigger, and indeed
that’s permitted under the Big Bang too, which just say those parts of the Universe
close enough for us to see used to be finite in size or even point-like, we don’t know
that the whole Universe might not be infinite in size and might have begun that way too,
we just know it’s much bigger than the parts we can see and that those used to be way smaller. So throughout the 1940s, and 50s both models
were quite popular with scientists. The first hard hit to Steady state was the
discovery of quasars, which in general are much more common the further from Earth you
get, which means they were much more common in the past, they don’t get less common
closer to Earth because our region of the Universe had fewer of them, but rather because
they are almost all gone these days and we can only see the old ones because the light
is just reaching us. In the Steady State model the Universe is
expanding and gaining new bits of matter but is basically the same over time, so finding
a feature of the Universe that has significantly changed over time strongly implies the Universe
is not Steady and stable in its composition over time. So by the time we discovered cosmic microwave
background radiation in 1964, Steady State had already become the minority view of cosmologists,
though still had a number of supporters. Initially it wasn’t too bad a blow, as one
plausible explanation could be that it was light from ancient stars that had been scattered
around by galactic dust. However as we mapped it out better it became
increasingly clear that it was very evenly spread in all directions, so whatever was
causing it had nothing to do with our galaxy. When the Universe was a good deal younger
and a good deal more dense, basically a big hot plasma, light was constantly being emitted
by it but scattering right away. Just one big white-hot fog of hydrogen plasma. As the Universe expanded and cooled, it eventually
cooled enough to allow protons and electrons to bond to form neutral hydrogen gas instead,
which no longer interacted with all that light as easily. That light took off in every direction without
constantly slamming into things and scattering. For the first time, the universe became transparent. The light was emitted all across the universe,
sailing off in all directions and is now, 13.8 billion years later, arriving at every
spot of space, since you can always draw a sphere around any given object, like Earth,
that is just wide enough for light from that moment to be arriving,. We call this the Surface of Last Scattering
and expect it to keep getting bigger and weaker till the end of time. Nowadays it’s microwaves, hence cosmic microwave
background radiation or CMB. In the past it was stronger infrared waves,
long down the road it will be weaker radio waves. That was predictable by the Big Bang Theory
but not by Steady State or Static Models, so it didn’t quite kill them but it locked
the Big Bang in as the overwhelming consensus model. It still isn’t the only one, and it predicts
multiple possible ends for the Universe from Big Rip to Big Crunch, but it’s essentially
the state of play for the last several decades till now and still running strong. We’ll be exploring those scenarios and some
more evidence for the big bang in part two, and some more modern competing theories but
as I said, Steady state didn’t die entirely, and indeed we got something called the Quasi-Steady-State
model or QSS in the early 90s, which adjusted steady state to include mini-bangs, for instance,
instead of matter appearing in bits and pieces constantly, it pops up in Big Bang events
scattered far apart in time, but more like raindrops falling on a pond. Issues with this include why we can’t see
stuff older than the big bang, or local mini-bang, but indeed we often have had objects or structures
that at least initially appeared older than the Universe. This was particularly popular in what is called
Plasma Cosmology, a theory of modest popularity in the 80s and 90s that was a variation on
Steady State in the sense of the Universe having always been and always being, with
no end. Like many such models it didn’t handle thinks
like quasars or cosmic microwave background radiation very well, but as we reached more
modern times we also had to deal with both dark matter and dark energy, and we’ll look
at the impact of those as we move in to part two, just follow the link to part two over
on Paul Sutter’s channel. We’ll be back again next week to discuss
de-extinction of species and high-tech ecosystem preservation, for alerts when that and other
episodes come out, make sure to subscribe to the channel, and don’t forget to subscribe
to Paul’s Channel while you’re over their for part two and hit the like button for both
episodes. We’ll see you next week!
Seemed interesting.
Just had a hard time with the accent compounded with speech impediment.