This episode is sponsored by Curiosity Stream We’ve spent two hundred episodes discussing the amazing things that might be possible
in the future, but what about the impossible? So today is our 200th Episode here on SFIA! It’s been quite a journey to get here, and
I thought we’d indulge in some commemoration of the event, but in deference to any new
watchers here just for this topic, we’ll save that for the end of the episode, beyond
saying now just how grateful I am to everyone for making this occasion possible. We’re also about to hit the fifth anniversary
of the show in just under a month, and I wanted to thank everyone for all the inspiration
and well wishes over the last five years, and of course for tuning in every week. On the one hand, the topic of things which
will never exist seems an odd one for a show focused on discussing all of the awesome things
which might come to exist in the future, and I was surprised this topic won our poll for
episode 200, but on the other hand, we do often emphasize that our goal here is to look
at what might come to be, within the realm of known science. We rarely drift outside that and I always
try to announce it loudly when we do, because the difference between science fiction, science
fantasy, and scientific futurism is that focus on scientific realism. Probably some of the best known breaks we
have with science fiction is that in almost all sci-fi, you tend to have faster than light
travel, artificial or anti-gravity, and force fields, but these are examples of things we
have discussed in other episodes among our broad inventory of 200 videos, and I wanted
to cover new material today. While those last two, gravity manipulation
and force fields, might be possible under science we just don’t understand yet or
have analogues we might be able to create under known science, FTL seems to be a different
kind of impossible. Faster than light travel or communication,
which are tied to time travel as well, take a while to show how they aren’t just outside
known science, but actually rather contradicted by common sense as your understanding of the
Universe grows, as they are really the same as asking why a cause can’t happen before
an effect, why you can’t have 101% of a pile of rice, or why you can have a negative
dollar in your pocket, or a negative cup of water. Of course, you can have these things in mathematics,
but the physical world and the mathematical world are not the same places. Check out the FTL series for more details
about why we tend to be skeptical about ever having FTL or time machines. But speaking of mathematical worlds brings
up a different sort of impossible: places which may exist but which we may never be
able to see or visit. Concepts like string theory and the multiverse
work great in theory, and may indeed exist, but we have no inkling about how we might
look at or travel to them. They may indeed not exist outside of the imaginations
of very clever physicists. There is, after all, no observable evidence
of them; or they may exist and we may figure out how to observe or even visit them one
day. If not though, it is an interesting philosophical
quandary if they would actually be real in any meaningful sense. But there may be things in our own Universe
just like that. For instance, you can’t ever see an atom,
because they are smaller than the wavelengths of visible light. To really see an object, you need to use a
wavelength equal in size to or smaller than that object. The problem is, photons are counter-intuitive
when it comes to density. Taking some liberties here with the word “size”,
we can imagine a photon as big as or bigger than a planet, but according to our models
contains just a few trillionths of a trillionth of a trillionth of a joule, a joule being
the approximate energy needed to lift most handheld objects from your pocket over your
head. That infinitesimal fraction is spread over
a region wider than a planet, and would radiate in the Extremely Low Frequency Radio Bandwidth
range of a mere 30 hertz or so. The ELF band is used for submarine communications
and is also produced by lighting strikes and other disturbances of Earth’s magnetic field,
as opposed to the kilohertz and megahertz ranges we use for listening to the radio. When you think about how tiny an amount of
energy that is spread over such a vast region, it’s simply ethereal. On the completely opposite end of the spectrum,
we have x-rays, whose wavelengths are about atom sized, and gamma-rays, whose wavelengths
are about atomic nucleus sized - far smaller, and hugely more energetic. With these we can image atoms and subatomic
particles, but they have so little mass and energy themselves, and these photons have
so much, that you are utterly disrupting whatever you look at with them, even before we consider
quantum uncertainty. What if something were even smaller? We don’t know and it’s hard to say, since
we need yet smaller and more energetic photons to detect them. A photon with about a joule of energy all
to itself would be an Ultra-high-energy gamma ray in the exa-electronvolt region, with a
wavelength of just a bit under a trillionth of a trillionth of a meter, already more than
a billion times smaller than a proton. And yet it would contain a billion times more
energy than that proton, so it would be like trying to examine a golf ball by bouncing
a mountain off of it, and anything that small would presumably be even less massive. Yet it might one day be done. However, if you’ve seen our episodes discussing
micro-black holes you know that it is energy density, not mass, that causes black holes,
and in theory you could have a black hole a mere 10^-24 meters in radius, a trillionth
of a trillionth of a meter across. It would weigh about a ton, with all its matter
stuffed in there, and that’s a lot more than a joule of energy: about a billion, trillion
times more. By the time you’d get to 10^-36 meters,
as small to an atomic nucleus as that nucleus is to our planet, a photon of that wavelength
would be carrying around 100,000,000 joules of energy. That’s about the same mass-energy a black
hole that size would have, and its expected life time would be a mere 10^-45 seconds. How would you detect anything down at that
scale, as small itself to an atom as that atom to a planet, being hit by something carrying
as much energy as a freight truck on a freeway, and so dense that our photon actually becomes
a black hole? If you’ve ever heard of a Planck length
or a Planck time, the so called minimum units of space and time, that’s what those are
and why, more or less. We’ve good reason to think that nothing
smaller than that can exist in this universe, and that indeed maybe even black holes, normally
thought to be point-like at their central singularity, are actually constrained to be
no smaller than that. The Planck length is arguably the minimum
size that quantum gravity effects are able to be established, so nothing smaller than
that is expected to exist because it would lack the quantum interactions necessary for
it to exist by our definition of existence anyway. Also, to observe something smaller than the
Planck length would actually require a photon of such high energy that is expected to collapse
into its own black hole and disrupt anything that small we’re trying to measure. So while such tiny objects might exist, the
physical measurements and interaction of those objects with systems to detect them are impossible
using our laws of physics. On balance, though anything smaller than a
Planck Length or a unit of time shorter than a Planck Time probably can never exist. Now these Planck units, and there are many
besides distance and time, are non-coincidentally calculable by using combinations of five physical
constants, the speed of light, the gravitational constant, the reduced Planck Constant, the
Coulomb Constant, and the Boltzmann Constant. Planck units are considered our preferred
means of communicating physical properties to aliens, rather than metric or imperial,
as they are based off these fundamental physical constants. But they also often imply hard limits on reality
too, and not always minimums. For instance Planck Temperature is around
100 million, trillion, trillion degrees. That’s not only a lot hotter than any star
at its core, and hotter than anything we’ve done in a lab, and we can outdo stars in a
lab, but it’s thought to be the hottest anything could be, and probably the temperature
at the Big Bang. Nothing hotter can ever exist. Physics breaks down beyond that, as likely
do all the basic physical forces, though if we ever get a working Quantum Gravity theory
or Grand Unified Theory of Everything, that might change. There’s a popular and very flawed notion
of looking at the scale of the universe like a Matrioshka Doll, comparing atoms to solar
systems and so on, it’s handy for quick and rough analogies but often gets extrapolated
to imply deep significance. We just saw the bottom of that scale and how
it breaks down, but it does at the top too. We don’t know how big the Universe is. It might be infinite as we can only ever see
events in our Hubble volume, that expanding sphere around us in our expanding Universe
where things are not moving away faster than light. We can and have mapped the Universe significantly
further out by projecting our observations of distant galaxies that were within our hubble
volume when the light left them billions of years ago. The light from these distant galaxies has
only just reached us, but today, the space between us and these galaxies is expanding
at superluminal velocity. In the future, when the light leaving those
galaxies is slower than the speed at which they are moving away from us, they will vanish
from our telescopes. This is the Observable Universe, currently
47 billion light years in radius, which seems rather big since the Universe is only 13.7
billion years old, you wouldn’t think we could see wider than that, but remember everything
is flying apart, when we see a photon arriving from some source 13.7 billion years ago, we
were a lot closer to that object when it left. So it will be impossible to send a message
to anyone on opposite sides of the volume using radio or light, no matter how powerful
you make the signal, because light will never be able to catch up with the object it is
being aimed at. The difference between the Observable Universe
and a Hubble Volume is the latter is smaller and is inside our cosmological event horizon,
meaning we can see events that occurred inside it. Out past that, we can see stuff that has happened
but will never get any updates and could never send a signal or a ship that could reach it. So our maps of those objects that have passed
beyond our Hubble volume are estimates only. An accurate map of what the whole universe
looks like will never exist while we are bound by the postulate of causality. A critical concept there too, the speed of
light is really the speed of information, and its information that can’t be allowed
to move faster or backward in time, because it messes with causality, galaxies expanding
away from each other faster than that speed doesn’t violate that. In truth, we can only infer the existence
of regions beyond even that because we can’t think of any reason why our Universe would
be a sphere exactly that size centered around Earth. The whole Universe could be a little bigger,
or a lot bigger, or even infinite. When it comes to infinity, much like the infinitesimal,
not only can’t we ever get there but we won’t even get close. But before you get up to that scale, everything
gets rather plain and homogenous, we call this the End of Greatness, and that’s only
a few hundred million light years across, representing volumes not even a percent of
a percent of a percent of the Observable Universe. This is essentially the zoom point where there’s
nothing really unique anymore, such volumes are hardly identical to each other, but you
stop having unique objects that can really be thought of as related and meaningful the
way a galaxy for instance is. It’s the top of our scale as sub atomic
particles are the bottom, if you want to think of things in that sense of zooming in or out
and see a smaller or bigger version of the same thing, which again is wrongheaded and
inaccurate anyway. Of course if the Universe was infinite, and
you had an impossibly fast spaceship, you would actually begin to see genuine identical
repetition eventually if you traveled far enough. In an infinite system, you will always have
repetition of any pattern, the smaller that pattern the more often, and if we think of
a Hubble Volume as the maximum meaningful chunk of space – which would obviously not
be true if you had an FTL ship to be fair – we’d see that repeat eventually. See the Infinite Improbability Issues episode
for exploration of this concept, but the sticking point is that such being the case, you could
never actually know if the Universe was infinite and repeating randomly or actually a closed
loop of that size, and as we note in that episode, practically speaking it doesn’t
matter, if the infinite does exist, we can never actually experience or prove it without
breaking physics as we know it. This brings us to another thing which will
never exist, and that’s True Immortality. We talk about life extension a lot here, and
not just of mere centuries, we’ve contemplated millions of years of life or even outliving
the stars themselves in Civilizations at the End of Time. We talked about practical limits on even digital,
backed up minds in Digital Death, where you effectively get a half-life rather than a
lifespan. But true immortality requires the infinite,
and even if you could find a work around to the Heat Death of the Universe, there’s
always a finite chance of death no matter how robust and sturdy you are or how many
backup copies you have, and over infinite time, the Grim Reaper will eventually get
you. Of course with infinite time and space, he’d
spit you back out again too, even if just as a deluded Boltzmann Brain that coincidentally
had randomly assembled memories identical to your own at this moment. A Boltzmann Brain is a self-aware entity that
arises by chance because of random fluctuations. In an infinite universe with infinite time,
the creation of even the rarest things become possible. But continuity can’t be achieved regardless
because you have to be able to store and sort all those memories and eventually you hit
a wall where you’d need all the mass of a galaxy to store your memory, or more. Another thing that can’t actually exist
is what we call the Library of Babel, an extension of the notion that an infinite number of monkeys
with typewriters will eventually bang out a copy of Shakespeare’s classics by random
typing. Of course they’d also have banged out every
other book too, including far more copies of random gibberish, which together make up
the Library. There’s simply too many unique combinations
of letters in a book. A typical thick novel might have a million
characters in it, and even if we limited those characters to the 26 lowercase letters, a
space, a comma, a period, and an apostrophe, 30 characters, you would have 30^1,000,000
possible combinations. If those were each in one kilogram hardcover
books on shelves, that library would mass around 10^1,500,000 kilograms, a mass that
is so meaninglessly huge that it dwarfs the mass of Observable Universe by far more than
that Universe dwarfs an atom. Indeed even if you stored each character of
the books on a single atom instead of a bit of paper, you still would need untold universes
to store the Library of Babel on. So don’t worry about ever getting bored
from life extension, you’d never run out of new books to read. Admittedly most would be utter incomprehensible
garbage, but that’s only a slight step down in quality from a lot of books I’ve had
the misfortune to read. Speaking of bad fiction, this is another type
of impossible things which are possible but just really unlikely in any practical sense,
and we see many in science fiction. Anthropomorphic portrayals of aliens can be
accurate in a sense of having some similar thinking, as you’d expect technological
civilizations to need some similarities of attitude to crop up, like curiosity and teamwork,
but visiting an alien planet where you can reach up to an alien tree and eat an alien
apple and shake an alien hand is not too likely. It’s far more likely that if the atmosphere
didn’t kill you that the chemicals in the food would. So you might grasp their tentacle while wearing
a hazmat suit and they might reply with their own traditional greeting of vomiting on you
to share their meal in the spirit of unity and friendship, but as you’re running back
to the airlock and decontamination shower at a gallop before the acid eats through your
suit, you’ll probably decide future conversation can be had remotely. And indeed probably only through computer-translated
texts, since their equivalent to speech might not be just sounds you can’t reproduce with
your throat or hear with your ears, but involve ejecting different flavors and acidities of
spit at you. And while it’s common for scifi to show
problems for live diplomatic events where you accidentally insulted some bizarre custom
of theirs, that’s probably an understatement. I doubt their diplomats and traders would
be any more easily offended than ours, but they might ask if you could please stop breathing
in public every few seconds, or getting irked why we seem bothered at them relieving themselves
in the middle of a conversation. For this same reason I’d say interspecies
romance, a staple of science fiction too, is off the table, but I never ceased to be
amazed at all the strange stuff people are into. This sort of possible but impractical limitation
applies to a lot of other ideas too, not just light sabres and melee combat, bringing a
knife to a laser gun fight, or giant war robots, but things like teleportation too, where even
when we’re discussing versions of it that involve copying a person from some digital
recording, or even just a digital recording of their mind, the sheer bandwidth involved,
and energies needed for a rapid scan or rapid print, is likely to often make it infeasible
if technically possible. Many times even when we say technically possible
we really only mean on paper anyway, and a perpetual motion machine is for instance possible
on paper, since while we often use that to mean something that can generate free power,
its basic form is something that just keeps moving without slowing down, and of course
that’s fine under Newton’s First Law, the core of physics itself. An object in motion will stay in motion, unless
acted on by some other force. But there’s always some other forces around. Forget about friction on a spinning wheel,
even a sphere turning around in the vacuum of space will eventually slow down, because
there is no true vacuum, and even in the quantum sense there’s random stuff popping in and
out of existence all the time. Interesting side note, since so many classic
scifi space battles involve fighters dogfighting like jets in an atmosphere, I’ve seen some
fictional settings justify this cleverly with etheric rudders or similar, and with all that
quantum bubbling going on, it is vaguely conceivable someone might find a way to interact with
that strongly and thus make a rudder or fin that could pivot around by plowing through
that. This might also permit a reactionless spaceship
drive, which could be very handy. Critically though, even when there’s nothing
there’s always something, something to make stuff break down or act less efficiently,
so objects built to last a trillion years without repairs are unlikely, and we spent
last episode just talking about all the extra maintenance space stations, megastructures,
and spaceships have from wear and tear happening in empty space. That applies to another popular notion for
immortality and resurrection, the idea that a sufficiently powerful computer could reconstruct
the long dead, sort of the reverse case of predicting the future by predicting every
action or even every particles motion. A fairly dark example of that is Roko’s
Basilisk, where a technological singularity quasi-violates causality by threatening people
in the past not to interfere in its eventual creation or it will resurrect and torment
them. That’s a pretty crazy notion and some folks
get worked into dread worrying about it, there’s no need though, no computer could ever do
it. We explained how the future prediction angle
could never be done, no matter how powerful the computer, in our episode on Psychohistory,
and for much the same reason that the Library of Babel can’t exist, even if you kept it
more modest, like only allowing actual words not random characters or only books a few
pages long. There’s just too many permutations, even
ignoring quantum, which we can’t. See, a person buried in the ground doesn’t
stay that way for long. It’s a bit morbid to say it but your brain
is gonna get eaten, and it’s gonna decay and outgas, and those bugs are gonna exhale
and inhale and excrete and die and get eaten, and good luck tracking the vectors on those
particles. Freeze someone or get them fairly fresh and
sure, but don’t go hoping to ever meet a resurrected Ben Franklin, I’d give time
travel better odds than that. That’s not to say we wouldn't cheat if we
ever got the ability to see the past, not even travel there, but detect all atoms and
energies at a particular place and time. We could resurrect a copy of Ben Franklin
at the moment of his death, or very soon after. It wouldn’t be Ben Franklin, but the copy
would stake their life on the fact that they were, so perhaps it wouldn’t matter. Ultimately, we can’t of course say what
is or isn’t possible, there’s always room for surprise, but we can try to look at what
might be possible under known science or how we can achieve something similar or even better
than the wildest dreams of scifi without needing radical changes in our understanding of the
Universe. Or we can speculate on an example of such
a radical change or technology and see what it might imply, and that’s what we’ve
tried to do over the last 200 episodes and what I hope we’ll be able to do for another
200. Certainly there’s no fear of running out
of stuff to talk about, we only scratched the surface of most of these concepts today,
and the future might not allow anything we can imagine, but it certainly allows a lot,
and seems to offer us new dreams to explore every week, so we’ll keep on doing that. Folks say that when it comes to the future,
the sky’s the limit, but as we say here on SFIA, it most certainly is not. So 200 episodes now, each its own documentary
effectively, and I wanted to talk a bit about that journey, but first, if you have seen
all 200 episodes and can’t wait till next week, try out Curiosity Stream, with over
2400 documentaries on science and learning from some of the world’s best filmmakers,
Curiosity Stream offers a vast supply of thought-provoking videos on many fun, educational, and inspiring
topics. Given our topic for today, I’d particularly
recommend Journey of the Universe, a chronicle of humanity’s journey to understand our
universe and the math and physics that helped us find out what was possible. You can get unlimited access starting at just
$2.99 a month, and for our audience, the first 30-days are completely free if you sign up
at curiositystream.com/isaacarthur during the sign-up process. So I mentioned at the beginning I wanted to
talk a bit about our own journey of the Universe and 200 episodes after our show today, and
thanks for joining me for this aftershow. If you’re curious about why we picked today
topics, we ran a series of polls to see what topic we should commemorate the 200th episode
with, and to my surprise the winning topic was “Things which will never exist”, given
that we normally focus on awesome things that might exist in the future. Perhaps that’s appropriate, and interestingly
the episode was selected from 67 topics the audience over at our Facebook Group suggested,
with the top 5 being polled here on Youtube. The topic was actually suggested by our longtime
cover artist, Jakub Grygier, who was the first person to start helping me out on the show
way back around episode 20 in 2016, about a year and half since our very first episode
and also about when we started doing weekly episodes. Since we started that, we haven’t missed
a single Thursday weekly release yet, and much of the credit for that goes to many folks
who’ve since joined up to help out making the show. I should note though that episode 200 is kind
of debatable. A couple years back when we started putting
together a large team, I started writing each episode a couple months in advance to allow
plenty of time for script editing and graphics. To keep organized, I assigned each episode
a number in order, as the titles often changed between initial brainstorming and when they
aired, on the episode chronology sheet that we track that all on and which I’ll link
below. You’ll note the entry is way past line 200,
and that’s because I eventually started treating the number as more of the production
week, so bonus episodes, collaboration with other shows, interviews, and so on all get
the number plus a letter. And many of those bonus episodes get written
long after the regular episodes which follow them, so I just squeeze them in to the chronology. I could think of about 4 different ways to
properly count the episodes, and had long since decided we’d let the audience pick
our 200th episode, or episodes in a way, so amusingly this is actually our fourth celebratory
episode in a row, our last three were also poll selected and last week’s episode was
the poll winner over on our Patreon page. Let me give them a quick thanks too, the thousand
or so folks whose generous donations fund this show are one of the biggest reasons we’re
celebrating 200 episodes today. If you’ve ever wondered why the occasional
extra episodes that throw off the count are called Bonus Episodes, it’s because the
first few were made specifically to reward our Patreon Supporters, who normally get charged
for each weekly episode and not those. I think it speaks a lot to the character of
folks who give up their hard earned money to support this enterprise that when I offered
the option of having them alone get to see those bonus episodes first, since they were
my way of thanking them the resounding consensus was no, let everyone see them right from Day
1. From years of being on Youtube and getting
to know other channels, I can say that spirit is not universal by any means, and I am beyond
grateful for having an audience that has a reputation among other science and education
shows for their enthusiasm, involvement, and courtesy. From all the folks who help out on the show
to every discussion on our social media forums to every comment left on each episode, you
are my inspiration in so many ways. I want to thank all of you for joining us
every week for the show. I still remember when I got an email from
Youtube telling me I had a subscriber, and asking what the heck a subscriber was, and
as a few more rolled in, thinking how neat it was that there were hundreds of folks who
shared my interest in exploring the future. Now that the show has hundreds of thousands
of subscribers, all I can say is thank you for joining us, thank you for making 200 episodes
possible, thank you for inspiring me, thank you for watching, and we’ll see you next
week!
Our 200th episode, thanks everyone for watching every week and making this thing exist :)
TLDR: FTL Travel, wormholes, accurate simulations of the future, fully "compatible" alien biology, complete immortality, anything above/below Planck units (besides Planck mass), an up-to-date map of the observable universe, the ability to send anything beyond the Hubble Volume, anything infinite, the Library of Babel, teleportation, perpetual motion
In the video it is mentioned that the Library of Babel will never exist, not even when we limit it to a few pages or a small number of possible characters.
There is a site called Library of Babel which uses an algorithm to produce every possible variation with a maximum length of 3200 characters. Why does this not qualify as a (limited) library of babel?
Killer episode. Thank you to your Patreon supporters for the bonus episodes hot off the press
What can't exist depends a lot on how speculative you're willing to get. The video says that true (infinite) immortality can't exist, even if we prevent the heat death of the universe. The idea is that there's a finite probability of death, and an infinite amount of time, so the probability approaches 100%. But how are we assuming we get around the heat death of the universe here? Are we stuck with a set amount of mass energy, but manage to reduce entropy? Or are we instead assuming we can get new mass energy? If dark energy is a continually created energy of space, then conservation of mass and energy isn't actually true over the entire universe. If we could somehow utilize dark energy to do work, we could set up a system that copied us indefinitely across the infinitely expanding amount of space. As time approaches infinity, the number of copies also approaches infinity, and the chance of true death (defined as every copy descending from the original being destroyed) approaches zero. I'm not going to bet my life on the laws of physics actually allowing this, though.
Happy 200th and Happy Arthursday everyone :)