Articles, Blog

Time Travel

January 4, 2020


This episode is sponsored by Skillshare I had a really good time travel joke to start
the episode with, but it turned out none of you liked it. So today we start off our sixth year here
on Science and Futurism with Isaac Arthur, and I am your host, Isaac Arthur. As we travel from 2019 to 2020, Time travel
seemed like a good topic, and I figured we’d start by discussing why we don’t think it
can work under known physics, then talk about what the implications would be if it turned
out we were wrong. Of course[a] the thing I always take as the
biggest proof time travel isn’t possible is that nobody is offering package deals for
temporal vacations. If time travel were possible we should see folks from the future and the
past everywhere, and every when, and not just a few secretive folks with a time machine
like we see so often in science fiction. People don’t really seem to look much at what the
extended and expanded use of such a technology would be. While that may be forgivable when
a story contains such technology having just been invented, so everything revolves around
a prototype or its first use, this doesn’t really work with Time Travel since its being
invented and used at any point means it’s basically been invented and used at all points
in time. If you managed to invent time travel, you ought to be able to walk out of the machine
a moment later and be welcomed by all your admirers and descendants from when you hopped
back in time to, say, cure smallpox or similar. Needless to say, a lot depends on how time
works, which depends a lot on what time actually is, and honestly we still don’t really know.
We’ll try to look at how time travel might function, or not function, under a few of
the main concepts folks have offered for explaining time later in the episode.
First though, let’s talk about the issue with time travel under modern relativity,
and then under modern quantum mechanics, where they don’t quite match.
In relativity, time is a flat linear thing plodding on at a set rate in the same way
planets are flat; which is to say they aren’t, unless you build one that way, but they usually
look flat, or fairly flat, at low altitudes, get up high and it doesn’t look flat at
all. Space-time, on the other hand, looks rather flat at low gravities and accelerations,
but when those are high it doesn’t look flat at all.
On a curved planet you also can only see so far because of the horizon, and something
much the same applies to space-time curvature. The ‘edge’ of the Universe is actually
our cosmological horizon and as far as we can see, but we’re pretty sure it keeps
going on a long way after that. As we look further from Earth in any direction we see
objects receding away from us at faster and faster speeds, eventually so fast they can
no longer be seen because space expands between us and them faster than light can cover the
new space being added. Or so we assume, we obviously can’t see
those places, but if it didn’t we’d actually be at the center of our Universe. And indeed
we are when we normally reference the Universe as that’s shorthand for the Observable Universe,
which practically speaking is all there is since we can never see or speak to or travel
to the rest, without some sort of faster than light technology.
The problem is that the faster you go, the more energy you need to get to that speed
and the more you need for each increment higher. More and more of your total energy is of the
kinetic or potential variety, rather than mass-energy, that E=mc² thing. The more your
total energy is not mass, the slower time is passing for you. If you look at some object
that appears as stationary relative to you, like say a coffee cup you’re holding, all
of its energy is just mass energy. Almost all anyway, there’s a little heat energy
in that warm coffee which is trivial compared to its mass energy, which is the rough equivalent
of a dozen megaton hydrogen bombs, hence why coffee is so great for giving you energy presumably.
If you were to add an equal amount of kinetic energy, or speed, to that coffee cup, it would
now have half of its mass energy in the form of kinetic energy, zipping along at 86% of
the speed of light. Since only half of its energy is now mass energy, it will experience
half as much time as would a stationary object. If we were to double the cup’s kinetic energy,
with only one-third of its energy being mass energy and two-thirds of its energy is kinetic,
and the cup would experience time at one-third of a stationary object – and it would be rocketing
along at 94% of the speed of light. It’s impossible to actually reach the speed
of light because it takes more and more energy – kinetic energy – for each percent closer
to light speed you go. It took the same energy to get from 86% of light speed to 94% as it
did from starting at rest and up to 86%, and in fact it takes 7 times that to get to 99%,
22 times that to get to 99.9%, and 70 times that to get to 99.99%. So we say you can’t
get to light speed because you’d need infinite energy to do that.
But I think this sometimes gives people the wrong impression that you could actually hit
light speed if you just had some phenomenal power source. Mass is essentially what experiences
time and things without mass, like photons or gravitons, experience none. All objects
split their energy between motion through space and motion through time. How much time
you have pass is all about what portion of your total energy is your mass energy, go
99.99% of light speed and time runs at a 70th the normal speed, and I think it’s easier
conceptually to ask how you’d ever eliminate all your mass entirely, infinite power or
not, as that’s the only way you can move at light speed.
Time slows down until you hit light speed, at which point it stops entirely, and as a
result photons and gravitons and other light-speed particles don’t experience time, whereas
ultra-low mass particles like neutrinos, which move at nearly light speed, experience very
little time. If you could go faster than light, then by that relativistic equation, you would
be experiencing time not just very slowed down but running backwards. Again that’s
the usual explanation and I imagine most of you have heard it before, for my part I think
it’s a bit easier to ask first, how would you ever remove all your mass to be going
light speed, and second, how you would somehow have a negative mass to be going backward
in time. See the Things Which Will Never Exist episode for discussion of negative mass and
other negative quantities. It is not coincidental that virtually every
proposed type of faster than light travel relies on negative mass or energy, which we
have not yet detected or created a single particle of, contrary to some grossly inaccurately
titled popular science articles. For this same reason, we always point out that almost
all these methods open the door to time travel. When it comes to normal matter at least, we
could not move so much as a single atom at the speed of light if we used every bit of
energy in the entire Universe, and we’d need more than infinity to make it move backward
in time. We might get around these issues somehow one
day, but hopefully it’s a bit clearer why FTL and time travel so often get phrased as
an impossibility not just some technical issue that can be solved by sheer determination.
It’s not like traveling to the Moon, it’s like making 2+2=5, and when we say this or
that theory might allow FTL or time travel, what we usually means is that the theory doesn’t
explicitly forbid it thus far. One of those methods that does get kicked
around is using a wormhole, and those require the use of negative mass or energy, and actually
only let you travel back in time to when the wormhole was created, a result of closed time-like
curves or CTCs. This is a worldline, or path through space-time, that leads eventually
back to the exact same coordinates in space and time. Think of it like any curved path
you might walk down and end up coming back to where you started, like a circular running
track, only you also come back to when you started.
Now assuming we had this option invented, somehow, it might make for some interesting
civilizations. You can’t go back and see the dinosaurs or end some war in ancient history
before it began, but you can go back to the moment it was invented and built. Isaac Asimov
uses this sort of time travel in his novel The End of Eternity, which happens to be my
favorite book by him. There, a group of time travelers called the Eternals, who live in
a pocket of space-time, and can travel anywhere inside time between when the device was invented
till the end of the Sun, and use the death throes of the sun dying as their power source
for time travel. The book spends a fair amount of time looking
at how that impacts civilization, since they are not secret time travelers and actually
engage in trade between centuries. Indeed that was the original purpose and they later
began trying to change events to engineer better futures by making very tiny and calculated
changes, like sabotaging someone’s vehicle not to start up before they’d have gone
on to attend some major event that shaped them into being a dictator or similar. You
can see our episode, the Butterfly Effect, for an idea just how small you could make
a change and expect it to have world-altering effects a few centuries down the road. Trying
to predict those in terms of an outcome is far harder of course.
We’ll discuss that scenario for a civilization, one that can travel back to the time such
travel got invented but not before, in a bit. First though, I mentioned quantum mechanics
is a bit different than relativity for time travel and it actually offers us many pathways
that could either allow time travel or just sort of trick us into thinking we had. One
of those is the notion that you aren’t traveling to your own past but one very similar, out
of the multiverse concept of the Many-Worlds Interpretation of Quantum Mechanics. We’re
not going to get into the weeds of how Quantum permits, or might permit, time-travel, but
here you’re not actually traveling to your own past so you don’t have to worry about
the Grandfather Paradox, because it’s not your past you’re changing, just something
very close to it. The grandfather paradox is where you go back
in time and accidentally kill your grandfather, I assume accidentally anyway, and as a result
are never born and can’t travel back in time to kill him. Needless to say that’s
an extreme case but it’s the notion that something you do in the past would cause you
not to be able or interested in doing the trip after you made that change. You travel
back in time to save JFK from being assassinated and now you no longer have a motivation to
do so. Against that we have the self-consistency
principle, which is that you’d inevitably have events between when you went back to,
and when you left from, play out so as to make the trip still happen. Conceptually this
is like water evaporating from the ocean and falling down as rain on land. That water can
take any number of paths back down to the ocean again but still gets there. For instance,
you go back to next week with today’s winning lottery numbers but write yourself a note
saying you need to make that trip. It’s not that any given action is predestined to
happen the same, just that only those various sequences of events that lead back to causing
you to get into that time machine actually continue to exist while all the others essentially
poof out as hazy possibilities that can’t exist. The raindrop can fall many places and
follow many courses to flow to the same place and time. Many timelines are possible but
only those that lead to a self-consistent time travel event can be stable and exist.
That one works a bit better under the Copenhagen Interpretation of Quantum, which is the Schrodinger’s
Cat version where it’s alive and dead simultaneously till observed, as opposed to Many Worlds where
in one universe it’s alive and in another it’s dead, and you just don’t know which
one you’re in till you opened the box and checked. As an analogy to self-consistency,
events are in quantum flux till observed, like with the cat, at which point only one
possibility has happened and the others wink out, and only a self-consistent time travel
event could be observed. This presumably results in no option for paradoxes, always a problem
with time travel, as no paradoxical sequence will not wink out.
This paradox issue is a sore spot in some science fiction franchises. What exactly was
the point of the crew of Voyager going back in time to fix histories they didn’t like,
when it was made clear elsewhere in the franchise that this wouldn’t change their history
at all, only create a different history for someone else to enjoy, one among infinity?
Another, more interesting possibility for paradox avoidance is that as the Many Worlds
branch off from one another, some branches are pruned. Only the branches that contain
no violations of the laws of physics or logic remain on the tree. And so, if you did try
to kill your grandfather, then starting at the moment of his near death, the universe
would branch into the histories where you succeeded and the histories where you failed,
and only the latter would survive. What you would experience would be frustrating failure
after failure, because no matter how bizarre or contrived a coincidence was required to
prevent you from killing him, only the histories in which you failed and he produced your father
would be left. If this is true, there’d be no reason for time travelers to worry about
causing a paradox, because the universe absolutely would not let them.
And indeed you can argue it can’t possibly be your true past anyway because the Universe
we’re in has a set amount of matter and energy and if someone from next year just
arrived here now, they’d be adding mass and energy, mass and energy that is interacting
with stuff like producing gravity. So even if we transported you back in time to some
sealed underground bunker that little extra mass is slightly altering the Earth’s spin,
how much gravity it exerts on the Moon, and so on, changing the future, even if apparently
very little. Little effects can have massive long term changes, again see the Butterfly
Effect, but from a multiverse perspective it’s a different universe if even a single
atom is not exactly where it otherwise would have been.
Conservation of mass and energy isn’t the entirety of it, you can’t get around this
by just exchanging equal masses of material between two times, they’d have to be identical,
the same state, to switch and not produce changes to the state of the Universe, and
throwing something backward in time to replace something identical in every way, which would
include positions and state of memories in a brain or harddrive, is not meaningful time
travel. So you couldn’t just teleport data from tomorrow back to today on your harddrive
so it told you tomorrow’s lottery numbers, even though you wouldn’t seem to have changed
the mass or energy of the universe. And indeed that sort of quantum teleportation, changing
the states on bits on a harddrive, is one of those possible FTL or time travel notions
that gets kicked around and probably would not work.
Another ‘cheat’ approach to quantum time travel is that even though the odds of it
are beyond minuscule, there’s always a chance of things assembling effectively at random.
So you could have a bunch of atoms randomly assemble into a person with memories of being
from the 22nd century. Those odds, while again vanishingly small, are still larger than the
total number of universe combinations in a multi-verse where everything that can happen
will happen, so if Many Worlds Interpretation is correct, there are universes where someone
identical to you right now has emerged in the time and place your grandfather and grandmother
first met and interrupted their date raving about being transported to the wrong date
and causing them not to meet and fall in love. No grandfather paradox results from this though.
There’s also one where you think you’ve invented time travel, blow yourself up turning
the machine on, and a copy of yourself identical to the moment you threw the switch appears
at the intended destination time and place, smugly convinced the machine worked. See the
Infinite Improbability Issues episode for more craziness associated with Multiverses,
but while that technically isn’t time travel, it effectively is for all practical purposes
except the paradox, and of course not being something you can really choose to do.
Okay, that’s the not-too-quick overview of the mechanics of how time travel and paradoxes
might or might not work, let’s consider some scenarios for those if they did work.
What sort of civilization gets produced? First, if the multiverse approaches work,
and lets you just travel there, adding mass and energy to some place when you arrive,
this becomes really good news because it means the number of possible Universes is now infinite,
rather than just very large. Many-worlds generally assumes there’s a Universe for every single
possible combination and arrangement of each particle, that’s a huge number but not infinite
because the mass of the Universe is assumed to be finite, at least the pocket we call
the Observable Universe. If I can add an atom to that, I now create
even more universes. One might argue it’s still not actually infinite since you can
only put so much matter in the Universe without collapsing it into a black hole, but as the
Universe expands that amount increases. You also get FTL travel out of it, since you can
jump back in time, move in a direction, jump back again, move again, and so on until you
are at a destination, like the Edge of the Observable Universe. So the number of possible
realities you could visit and colonize is either infinite or so large it makes no difference
and you never have to worry about the Heat Death of the Universe because you could add
or subtract mass and energy and entropy from any given time, or just move to a different
one. Under more classic time travel you can avoid
heat death too, by invading your own past. If the world was about to end you could jump
back to when it was younger and colonize that, and it’s presumably fine to do so since
you can’t do it if paradoxes are a problem as you’d erase the civilization that produced
you and your time travel device. At the cosmic level you just jump back to
a billion years after the Big Bang every time you run low on material. You might be wondering
if that proves time travel can’t happen since clearly no one did that, but logically
that doesn’t quite hold up as it’s a bit of a tautology, circular reasoning, which
is kind of appropriate for contemplating circular bits of time I suppose. If the universe permits
no paradox of this type, time travel isn’t possible so it doesn’t matter, but if it
does it’s because you are getting new realities out of it, and there will be realities for
every possible scenario including a reality that never had time travelers arrive in it
prior to time travel being invented there, we’d just be in such a Universe. Or one
where the footprint was minimal. Of course you also have the Self-Consistency
angle as an option too, you jump back in time and colonize the Early Universe but the pattern
of possible futures leading to us only allows the ones where we’d be ignorant that occurred,
like they died off or grew very slowly and distantly from us so we hadn’t noticed these
temporal colonists yet. Tenses are rather confusing in time travel
too, how do you refer to your own future that is your world’s past or vice versa? I often
get a bit confused when writing scripts on the show just because I often refer to things
like last week’s video, also discussing problems with Time, which came out December
26th, except that it is not January 2, 2020 as I write this, it’s October 28, 2019.
When I finish writing this script and upload it for the crew to edit, I’ll get to work
on making the video for November 7, Cybersecurity, it can get rather confusing at times and yesterday,
Sunday October 27th, I was doing a live chat session after our livestream on our Discord
server and started referencing people to our Space Pirates episode for a detailed explanation
of what I was discussing at that moment, only that episode hadn’t come out yet. I’ll
also sometimes reference episodes that don’t exist, because some bit of material got removed
from the draft for time constraints or to improve the flow of the episode, and I forgot.
Those unused scripts or versions of scripts are similar to timelines that never happened,
due to changing time, and presumably there are ones where those episodes were made.
That’s probably a small hint at the sort of tense confusion time travel civilizations
would get. How do you refer to something you plan to do yesterday, or that you already
did tomorrow? If this sort of travel is common and non-paradoxical, because it’s a sequence
of multiverses, how do you phrase an explanation to your friends when you come into the office
in the morning sporting much longer hair and beard and say you just came out of a timeline
where your wife died in a car accident so you had to skip back and fix that, and how
it was a very nice funeral and then the two of you went on a vacation afterwards because
it was a bit stressful. How about when a longer-bearded copy of your
co-worker Bob walks in and say it’s going to be a busy day, and then one with an even
longer beard comes in and says, “Good news everyone, tomorrow we closed the deal with
our new client, but we all need to do some extra overtime last weekend”.
It would tend to seem like cohesive timelines would utterly breakdown too, and you might
get weirder day-to-day options like dating apps that let you swipe forward or back, instead
of left or right, to find the girl or boy of your dreams from a different century and
sit down on your first date and see what your future would look like.
Now in fiction we often get some sort of rules preventing tons of time travel, concepts like
inertia of future events or changes requiring more effort the further back you seek to make
them. But often it’s actual legal rules, and that’s problematic because it doesn’t
really seem enforceable to have temporal police. Someone just goes back in time and prevents
them being formed. If they’ve got some widget that prevents such things happening, some
sort of time shield, then they can presumably build a bigger one that protects their whole
civilization too and folks can go do as they please elsewhere.
I get a time travel device and nothing is stopping me from taking some classes in Latin
and Roman History, grabbing lots of textbooks and schematics and modern widgets, and jumping
back to Caesar’s day and setting myself up as Emperor, or jumping forward to the future
to get some life extension treatments and awesome cybernetic enhancements and then jumping
back to the past to set myself up an immortal leader. If you do have that infinite number
of timelines option, this might be a better alternative to virtual realities where you
can be whatever you please as it might be cheaper and easier and more real-feeling to
just hurl folks to other timelines. There should always be one where the only difference
with your normal history was that someone identical to you popped up at a given time
and place, at which point it diverges. We usually say technologies like FTL and time
travel only exacerbate the Fermi Paradox, the big question of where all the aliens are,
because it now means you have to contemplate aliens from a much broader region of space
and also ones from the future jumping into the early universe. But this is one alternative,
that nobody spreads out to the stars because they just colonize earlier parallel histories
of their own world, and we just happen to live in a timeline where that hasn’t happened.
Confusing stuff that’s giving me a headache, so I’m going to close out here and get to
work on the Cybersecurity episode for November 7, 2019, which I already finished as I record
this on November 1st, 2019, but first let me wish you an excellent 2020, now that 2019
is over. When contemplating time travel, or fantasizing
about it, which I imagine I’m not alone in doing, one common problem is all those
missing skills you’d need to actually have to live back then, whenever then was. We have
a very skilled based society compared to prior eras but they had a lot of skills we generally
lack, so if you just popped up in some ancient kingdom you’d have a rough time surviving
without knowing the language or how to do things like grind grain or swing a sword around.
But we do live in a far more skill-based society than in olden times and it’s always handy
to be acquiring more skills. Plus it’s nice to just have them, even when they aren’t
meant for career purposes they offer fun new hobbies and a feeling of confidence that you
can get stuff done. That’s why I like Skillshare. Skillshare
is an online learning community with thousands pf classes in a wide range of topics like
design, business, technology and many more. Even just those focusing on productivity or
time management, like Thomas Frank of College Info Geek’s course, Productivity Masterclass.
A premium membership is less than $10 a month and gives you access to that course and all
the rest, and you can try it out for free. Join the millions of students already learning
on Skillshare today with a special offer just for my listeners: Get 2 months of Skillshare
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access to thousands of classes for free. Act now for this special offer, and start learning
today. So that will wrap our show up for the day,
but we’ll be back next week to our alien civilizations series to take a look at alien
conspiracies and aliens who conspire, and ask what sort of motives they might have for
a given conspiracy. The week after that we’ll return to the Moon, to look at what industries
might arise there and help us develop an interplanetary society, in Moon: Industrial Complex.
If you want alerts when those and other episodes come out, make sure to subscribe to the channel,
and if you’d like to help support future episodes, visit our website IsaacArthur.net
to donate to the show or look over our inventory of over 200 episodes or our awesome SFIA merchandise.
Until next time, thanks for watching, and have a great year!

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100 Comments

  • Reply DJ Khal Rhaego January 3, 2020 at 3:54 pm

    This was done really well! You have a talent with explaining the complicated…

  • Reply Dominic H. January 3, 2020 at 4:10 pm

    18:24 – Thank you!!! It always annoys me to hear that proof of time travel not being a possibility is that we can't see any time travelers. If causality is protected by each time travel backwards creating an alternate timeline/universe, time travel is still a possibility, we just either live in one of those timelines a single time traveler created – and a single instance of time travel who knows to what date would not be significant enough to be recognizable as time travel -, or in the original, protected timeline nobody can travel back to.

  • Reply Starfall 21X January 3, 2020 at 4:18 pm

    If time travel is possible because of many worlds. Then yes in the multiverse there are countless timelines, loops, etc where time travelers have been playing havoc with causality. This would also explain why there aren't people offering time travel vacations. And that is simply because we happen to be in a world line without time travelers.

  • Reply John January 3, 2020 at 4:24 pm

    everything good except the language thing. it isnt really a problem, if we had that problem we would solve it with some convention, adjusting words or coming up with new words. no need to make a big deal out of it

  • Reply Jonathan Fitch January 3, 2020 at 4:31 pm

    I was a little surprised that you got through an entire episode about time travel without a single reference to Dr. Who. Or was that the really great joke we didn't like?

  • Reply phil guer January 3, 2020 at 4:49 pm

    As far as I'm concerned,the only simple usefull time travel possible is the one where a new timeline is created each time you try to time travel into the past(or anything that already happenened and on which you have information).

    Once you reached another timeline(B) either you lock B out of your original timeline A with no way to go back.In that scenario,other people from the original timeline A can still go into any point of the timeline B and spoil you the future of A,but neither you or them can go back to cause a paradox. (Oneway timeline)
    Either you prevent A to reach the past of B,and once you're done you can go back to A .The present being determined by the matter from A the most advanced in time.When you go back in A,the time lock on B advance automatically.(Locked timeline)
    In the two case,you can't go back before the point the most advanced point that you have or could have observed in either timeline,which would cause a paradox. So if you go back to B,you will return to the present or the future but not the past.
    Of course,you can always go in the past of a copy of your original timeline or of B,but it will just be a copy.Unless you decide that all sentient creature share one soul,there is no selfish reason to help,for instance,the copy of you you will encounter.

    About geopolitical repercussion, it allow to flee your errors by hiding yourself in a Locked timeline in the past, rectifying the errors,and even coming back to the present or future of your timeline with an army if you're feeling good.

    If you choose a Oneway timeline,your ennemies may come chase you in the past( or future) ,and you will lose contact with every friend who didn't came.
    if your ennemies know where and when you teleported,they can go back several year in advance and build a prison around your arrival point,or if they don't know ,they will probably have to go back really far in time since they can't go in the past without creating a copy of the timeline.So they will probably build a new civilisation and maybe send some peoples in the future to try to assassinate you,but they won't be able to communicate with the past.

  • Reply TheNoodlyAppendage January 3, 2020 at 4:59 pm

    There are two problems with time traveller meetups. The same guy keeps coming back to eat all the chips, sp I have to go back in time to get some chips. The other is that they are usually spontaneous with a very narrow window between a fixed decision to have the meeting and the actual meeting itself. One must travel to the window between the final decision on the place and time and the time when it actually happens. If you travel to before the decision is made, the butterfly effect can change the time and location. and After the meeting its obviously not going to get you to the meeting. So if you have a machine that has some error rate, of say +/- a week, you can easily miss any meeting with less than a 2 week window.

  • Reply N&A Films January 3, 2020 at 5:08 pm

    Great joke

  • Reply Mau Vasconcellos January 3, 2020 at 5:14 pm

    Time travel is the main problem with the latest "Avengers Endgame".
    They say themselves: every time you change something, a NEW TIMELINE is formed, that is not your own.
    So, why the heck would you try to go back and collect all gemstones in order to fix a world devoid of 50% of the population, when you KNOW you'll be creating a new timeline, a new path that you WON'T be able to live in, once you travel back to your own timeline? You'll still have to live in this wrecked world that Thanos left behind, with no humans. "Oh, but it would give us a peace of mind knowing we helped another timeline…" Nah, cut the crap.

  • Reply id104335409 January 3, 2020 at 5:25 pm

    There is no such thing as time.
    As soon as you can free yourself from what you were thought all your life about time and wrap your head around that new concept, you will see how weird the whole time idea is when you look at it from aside.
    Kind of like the idea if God. Very hard to let go, but then you look back and ask your self Why did we needed that idea to make the universe work?

  • Reply Mike Ciappetta January 3, 2020 at 5:27 pm

    Isaac,
    Any plans on a video strictly on Space Force and the roles it may or may not play in the colonization of our Solar System?
    I love your channel!

  • Reply Matthew Grotke January 3, 2020 at 5:46 pm

    Disappointed that you did not discuss the explanation of time as discussed in the 2008 paper "Time for a Change" by Peter Lynds.

  • Reply Mayo January 3, 2020 at 5:49 pm

    In dec 2016 I witnessed a UFO. This is what my eyes saw
    Egg shape with pointy front.
    Went so fast it disappeared.
    Like it went into hyperspeed.
    It left track in the air.
    Not gonna say what kind of tracks.

  • Reply baigan kings January 3, 2020 at 6:07 pm

    Anyone from 2050??

  • Reply bean Soup January 3, 2020 at 6:09 pm

    univorse? multivorse? did not woak? — selective dyslexia?

  • Reply Ron Niabati January 3, 2020 at 6:12 pm

    What if you time travel to a part of the universe that is beyond your observable universe? Wouldn’t that be practically the same as time traveling to other universes?

  • Reply John Enslinger January 3, 2020 at 6:15 pm

    Thank you for always blowing my mind.

  • Reply DFX2KX January 3, 2020 at 6:18 pm

    "I had a really good time travel joke, but, it turned out none of you liked it."

    And that's where you're wrong.

  • Reply MisterTutor2010 January 3, 2020 at 6:25 pm

    What do want?
    TIME TRAVEL!!!

    When do we want it?
    .

    .

    .

    You know thd rest of this joke 🙂

  • Reply James Leon January 3, 2020 at 6:42 pm

    I liked the joke but it was the timing

  • Reply Ryan Holmes January 3, 2020 at 6:45 pm

    Time travel 😂. You would end up in the emptiness of space, light years from where you actually wanted to be.

  • Reply tracey adkins January 3, 2020 at 6:54 pm

    Grossly Mistitled Pseudoscience Articles in a Post-Truth Era.
    I'd read that one. Lol

  • Reply D. C. January 3, 2020 at 7:12 pm

    I know about time travel.

  • Reply Floyd S January 3, 2020 at 7:14 pm

    Quantum theory: you change the result by observing it, I would think that this alone says that the act of traveling back in time alone alters the future.

  • Reply Soonzuh January 3, 2020 at 7:20 pm

    Uni-wuss, how is that defined?

  • Reply Patrick Howard January 3, 2020 at 7:20 pm

    OK… time travel is possible… Consider… You can't carry enough fuel to accelerate anywhere near that fast… right?… So you have to figure how to accelerate without propellant. I have a 'science-fiction' gravity harness… Every particle, some to extremes beyond imagining and others barely feel a touch for eons, are affected by GRAVITY. I propose, that gravity comes in different types… Imagine that you're a a gravity wave from Earth… You get born/released from the Earth and move outward. You encounter our moon and help to warp space/time so that the moon does what it's supposed to do. But then what? We humans might think that wave just dissipates as it moves out… But I propose it does not… I propose that it becomes a 'differing' harmonic frequency resonance… Or somethin'… This wave, now a different kinda gravity, continues it's evolution and joins a harmonic resonance hierarchy that wends through the universe moving everything. It is something of a super-cosmic flow. A river of centrifugal acceleration, carrying every particle in existence. My ships 'gravity-harness' hitches to this different kind of gravity wave and we 'fall' to any destination in the universe. — Here is the good part. We navigators point our gravity detection equipment at the black hole in the center of Andromeda. And turn it on. In about a year and a half, We can initiate the spin maneuver for our own artificial gravity. With no resistance, we continue to accelerate to .001%C… (I really don't know at what point our mass increase becomes the reason for acceleration… But at some point… Our ship will become infinitely MASSIVE… Which will make us FALL infinitely fast toward Andromeda… Up to and past the speed of light. After crossing the light barrier… We are in effect able to traverse the entirety of existence including anywhen we set our navigation toward. A trajectory with a certain centrifugal acceleration will arrive at point in time, at a destination that a different trajectory will get you there tomorrow… or thursday… or 3854… — [I want to add a quick side note… As the harmonic resonance flows through space-time… The matter tends to accumulate in eddies and backwashes… galaxies… The spin of these galaxies is not regulated by the gravity of its own mass… But instead by outer-gravity harmonic resonance pressing in… We humans have incorrectly labelled the spin of galaxies as held in by dark matter… Or instead, the gravity from matter that we cannot detect. It is instead, the evolved accumulated gravity that has aged and joined the grand flow of centrifugal acceleration that moves every particle of the universe.] Also… The grand gravity-flow is quadrillions of times larger than the observable universe.

  • Reply Mark Smith January 3, 2020 at 7:35 pm

    The Head of Nixon always becomes President of Earth!

  • Reply ThermaL1102 January 3, 2020 at 7:52 pm

    time travel … right ….
    people in This time are sleepwalking through their lives , following a dead zombie without thinking about it for 1 second
    go back to any time … things won't be any different , only the god's name
    ''history'' still needs to start , for fucks sake … we haven't done anything , haven't learned anything , just sleepwalked around for thousands of years looking for help
    has it helped ?
    people need to wake the fuck up and start their lives , for once in their pathetic little lives

  • Reply 2old4gamez January 3, 2020 at 7:59 pm

    Anybody else watching this in 2019?

  • Reply Yeeeeeeeeeet January 3, 2020 at 8:01 pm

    This dude is the most euthastic person. Reminds me of my childhood haha

  • Reply grapy January 3, 2020 at 8:03 pm

    The intro joke got me real good. I thought he made a mistake then a moment later I laughed. Best joke in a long time. Thanks.

  • Reply Daniel Piechowicz January 3, 2020 at 8:07 pm

    I loved the joke!

  • Reply Alexas Machine January 3, 2020 at 8:53 pm

    Time Travel is in the Bible.

  • Reply Jon January 3, 2020 at 9:00 pm

    So many people are misinformed on this subject. You can travel faster than the speed of light. You just can't travel faster than light. If you provide enough thrust to accelerate at 1 G, your acceleration won't just start decreasing when you start approaching the speed of light from your frame of reference, only from an observer's frame of reference. This is because time is slowing down for you relative to the observer. Accelerating at 1 G, it would in fact only take 353.823 days to reach the speed of light from your reference. Don't believe me? Read the section on time dilation from this Wikipedia article on interstellar travel:

    https://en.wikipedia.org/wiki/Interstellar_travel

  • Reply Aryeh Katz January 3, 2020 at 9:25 pm

    could you make an episode about portals?

  • Reply Jose Canales January 3, 2020 at 9:59 pm

    HAHAHAHAH loved the intro

  • Reply Hal Anderson January 3, 2020 at 10:12 pm

    good video and everything but they way you talk makes you sound like a wetard

  • Reply Jon Snow January 3, 2020 at 10:31 pm

    1:41 "and honestly we still don't really know" We know very very little and even some of those the important ones are being questioned often with facts that are disproving them .. Science is freaking awesome!

  • Reply Oliver Smith January 3, 2020 at 10:35 pm

    Your parentage must comprise a very interesting unit considering your excellent name, and perhaps is also shows in your communicative skills and intellectual acumen. Not to rob you of your individual accomplishments. Thanks for sharing them.

  • Reply Oliver Smith January 3, 2020 at 10:42 pm

    Gods! I hope that coffee cup doesn't collide with Bertrand Russel's deific "English teapot" in it's orbit between Earth and Venus… Or was it between Venus and Mercury? And while the odds of in space collision are we know low, having already produced a high sub light speed coffee cup on top of Russel's teapot I want to register a nervous apprehension.

  • Reply Rebecca Armstrong January 3, 2020 at 10:42 pm

    the reason why no 1 has came back to this time is probably because we have simulations that are much safer and easier to enter where u can be god if you want … perhaps they actually put people in charge of a universe but erase their minds of entering the sim temporarily just to find out what type of person they are what better way to see if your a leader than by giving you ultimate power and seeing what you do with it .. I sure as hell don't want the Christian god in charge of gov as its been in charge once and it wasn't good

  • Reply Mr. Numi Who January 3, 2020 at 10:50 pm

    Nice popular topic, with the usual colorful misconceptions (it is not 'time' that you want to go back in – you can just run your time piece backwards for that. Time is a tool to track change, which is an aspect of reality (not time). Therefore it is 'change' that you want to go back in, or recreate (from a data set), or force backwards (in a contained system – that which contains all of the matter and energy of the previous condition) (and good luck finding it all). To go back in time is a notion for children (just to prod you out of your 'stupor') (consider that another prod – in order to place emphasis, and to hurry you up in your enlightenment, of which this is a small part). Otherwise you can continue not knowing what time is 1:38 .

  • Reply doogieAfro January 3, 2020 at 10:56 pm

    I can't put my finger on it but there is something about the english that throws me off and makes it hard to follow the line of argument.

  • Reply AnalystPrime January 3, 2020 at 10:58 pm

    You know the joke how the reason why lots of people came to watch execution of Jesus is because of all the time travelers? The wormhole trough time seems to result in similar crowd as everyone would be coming out of it at the same time, so you got Bob on his first date, Bob with his wife who is not happy to see him with his ex, Bob's soon to be ex friend Dan on his honeymoon with Bob's soon to be ex wife, and Bob with his new wife, coming to retry that first date that was interrupted when future Bobs and some unknown woman claiming to be his wife started arguing…

    There is an obvious logical fallacy in "FTL makes you go back in time" theory: the part of the math that says you get TT out of FTL is tied to the part of relativistic physics that says getting to or past c is impossible, therefore whatever method you use to bypass or bend the c limit must prevent relativistic effects, including time dilation. Therefore FTL makes time travel impossible.

  • Reply Gaz Tinsley January 4, 2020 at 12:20 am

    Your pronunciation of words is abysmal !
    Give up now !

  • Reply sickbailey21 January 4, 2020 at 12:51 am

    That might be the best segway in to an advertisement I've seen yet.
    You and your team continue to outdo yourselves, thanks for all that you do and I hope this new year brings you guys nothing but continued success.

  • Reply rldickie January 4, 2020 at 12:58 am

    I already watched this video next week.

  • Reply rRobert Smith January 4, 2020 at 1:20 am

    Title should be ….Why Time Travel is Impossible….no Mr. Arthur time travel is just a point on the science graph that we will soon pass up.

  • Reply Kenneth Hicks January 4, 2020 at 1:42 am

    Asimov just visited me… don't know if it was a dream or really happened… he told me to tell you to write books… and to answer your question, I don't know.
    Happy 2020 <3

  • Reply Otis Chapman January 4, 2020 at 1:43 am

    Is this guga foods second channel?

  • Reply MySerpentine January 4, 2020 at 2:10 am

    Time travel is a VERY bad idea.

  • Reply Your Face January 4, 2020 at 2:24 am

    Personal theory. Time is just the observation of entropy

  • Reply Peter Davila January 4, 2020 at 2:46 am

    Time Travel is happening all the time. Not by humans, in the typical sense from the movies, but by the "conscious agents" created by the Simulation. It is my belief that not only do we live in a simulation, but that our existence itself is not under control of our Free Will. Instead, it is under the control of the conscious agents that are integral to creating the holographic world that we get to experience. But, those simulation time travelers don't get to travel to the Past, since Time does not happen there. Time does not exist in the Past. That is, the simulation happens in the Now … They may have some ability to peak a short time into the future as part of what we understand as intuition, but their traveling in Time is mostly influencing just our Present Time. It is time travel in the true sense of the word, since any changes made in the simulation creates a new time line for a predetermined Arrow of Time for our "Avatars" to experience. Remember that time is an illusion, conveniently accepted by us because it has helped us and our conscious agents to survive the rigors of evolution. All of Time is always present, all the time, at the same time, Past-Present-Future. The only time traveling that may happen into the past is what may be allowed by the Delayed Quantum Eraser. The only time traveling that may be happening to future and back to present may be limited to the intuitive powers of the conscious agents …

    To explore these ideas further I have freely incorporated some of the concepts and work on Conscious Agents, as per the ideas and research of Donald Hoffman.

  • Reply FlamingTP January 4, 2020 at 2:52 am

    Time Machine Parts: Microwave, 42' CRT TV, Cell Phone, Retro Computer, Headphones. Tuttaru!♪ Time Machine Complete!

  • Reply Jay Man January 4, 2020 at 2:57 am

    Say Admire.. Say it😁

  • Reply Nighthawk Viper January 4, 2020 at 3:03 am

    I can beam you to Alpha Centrauri and have a destination delayed deployment receiver which has the ability to beam you back at a subsequent relative "time" you experience there, while Earthlings age at faster rates. Finding a relative time somewhere with inverse conditions would allow for rapid aging. Finding a place with both conditions juxtaposed; surviving such a transition will allow for time travel to Earth's relative time in the past.

  • Reply tim olson January 4, 2020 at 3:18 am

    My head hurts

  • Reply Shane Hebert January 4, 2020 at 3:22 am

    There was a time I was confused about this video. That was four weeks from now, the third time I watched this.

  • Reply Shaun Moor January 4, 2020 at 4:04 am

    Going back to with the adding mass to the past when time traveling altering matter/time .Does the mass theory not consider the fact that there is way more people on the planet than 1000 years ago? there for producing more mass. Maybe that's why magnetic north is moving.

  • Reply snodds88 January 4, 2020 at 4:05 am

    I enjoyed this video, thank you Isaac…

  • Reply Chuck Just Chuck January 4, 2020 at 4:49 am

    Well, that certainly gave ME a headache, Isaac… :-)_

  • Reply Pockets MacCartney January 4, 2020 at 5:00 am

    Just trying to figure out how someone manages to mangle the pronunciation of the word "wrong". Turns out, not interested.

  • Reply osoiman January 4, 2020 at 5:07 am

    For some good time travel fiction, I recommend City Beyond Time: Tales of the Fall of Metachronopolis by John C Wright

  • Reply jim bayley January 4, 2020 at 5:41 am

    What would you call one person in two places

  • Reply Mymy Lastname January 4, 2020 at 5:41 am

    This is being narrated by Elmer Fudd. Noice!

  • Reply Hexmark January 4, 2020 at 5:47 am

    OK that made my brain hurt and it caused me to spend 4 hours trying to understand a 26:20 min episode, FYI i failed miserably.

  • Reply crossbow indianna January 4, 2020 at 6:04 am

    Humans from the future+travel back in time=Aliens

  • Reply Booger Herrera January 4, 2020 at 6:10 am

    Is it just me or does he have a speech impediment?

  • Reply Jpound87 January 4, 2020 at 6:13 am

    What of a species that figured out how to encode all their though in photonic interactions?

  • Reply Hexi January 4, 2020 at 7:04 am

    Time travel is impossible, because time does not exist. It's a concept, not a force.

  • Reply countingpaperclips January 4, 2020 at 7:14 am

    That damn intro lol

  • Reply Phesheya Bhembe January 4, 2020 at 8:07 am

    Instructions unclear. Some guys just beat me up while telling me not to fuck with time.

  • Reply cuda70gt January 4, 2020 at 8:08 am

    at one time they said travel beyond 60mph is impossible….until it was done.
    at one time they said flight is impossible……until it was done

    at one time they said breaking the sound barrier is impossible….until it was done.
    at one time they said travel in space is impossible as you wouldn't have anything to push against…until it was done
    at one time they said faster than light travel is impossible………
    …………………………do they ever get tired of being wrong??

  • Reply 15gamers haven January 4, 2020 at 8:44 am

    After just finishing the expanse I thought it would be cool if you made a Sci fi book series and each book takes place 100 years apart or some length of time to have some important technological advances. The books can start with near future and early Mars missions but later on discuss intergalactic civilizations. Enough talking this is just an idea I had.

  • Reply heinzerbrew January 4, 2020 at 8:56 am

    You state that the fact that no one will ever build a time machine is proof that time travel is not possible. I'm not sure that being destroyed before you obtain the technology to time travel is proof that you could not have eventually created a time machine if you had not been destroyed.

  • Reply Peter Sloan January 4, 2020 at 9:02 am

    Who's watching this in 2120?

  • Reply Andrew Hoskins January 4, 2020 at 9:11 am

    What if whenever someone time travels, while their mass and energy are transferred to the previous time in space, it is exchanged with mass and energy from the destination? It can't possibly destabilize everything because it is an equivalent exchange, like a scale that is perfectly balanced, and is able to switch contents instantaneously. The scale wouldn't move.

    I mean that is the plot twist at the end of the original Fullmetal Alchemist anime, so I'm not the first person to come up with this idea.

  • Reply Mr.Nobody January 4, 2020 at 9:30 am

    in order to "travel" in liniar time , you have to go into the non liniar time , or hyper time …just like traveling into space you must go into hyper space to reach far destinations quicker … but of course we still dont know that time has more dimensions just like space , you cant "travel" in time without accessing higher time dimensions , every "jump" has to be made in and out from a higher dimension …but we are missing the notions to do that

  • Reply ThanksIfYourReadIt January 4, 2020 at 9:37 am

    One thing to note. Time doesnt exist. What most ppl think when saying time, is the force interaction betwean stuff according to the physica laws. But when stuff that interacts is dislocated (moving towards the speed of light), then these interactions have a harder time to connect and take effect. For this "lag" of exchange looks like a slowed down the sequence of happenings and titled time runs slower. Which means that physic interactions according to the universe constant laws happens less frequent then if you would stand still and would not hinder theire work.

    All and all time is just a word we use to describe physical law interactions, just like we call seemingly impossible to guess movements of matter, heat energy. And just like how we call seemingly impossible to backtrackable amount of calculation and information processing as "feeling".

    My guess is that the language and attempted shortcuts in information distribution and diverse knowledge background betwean people are the first step to forget what things are and would end up in a loop where we constantly reinvent already known things, constantly forgetting theire proper identity along the way, and eventually never getting to a conclusion that needs everything to be clear and clarified.

    The very fact that we even talk about any type of possibility of time travel suggest we already deep in a loop, and the way we bend the definition of time travel shows how we form the loop back to the point where we don't even know what we are talking about.

  • Reply Enclave Soldier January 4, 2020 at 9:38 am

    I find time travel to be an utterly silly concept. Who said time was a medium you can travel through? Time is just the way humans communicate chronological events. It isn't real.

  • Reply Ron Ackerman January 4, 2020 at 9:56 am

    Umm, ever wonder what UFOs are? Probably more likely time travel then Aliens

  • Reply Sad Toast January 4, 2020 at 10:17 am

    Oooohhhh this looks like a great channel for science fiction questions and discussion
    NEATO

  • Reply Jason Snyder January 4, 2020 at 12:30 pm

    What I would seek to prove is the subset intersection of quantum level and time loops. We live in a level of not understanding where we are 'alive' but don't understand what that means or how it is possible. We also have a lot of people having what are called premonitions and the notions of being able to see into the future have been in our folklore since since the first texts were written that survived long enough for us to know what they said today. Even I, someone with no spirituality, only interest in provable things, keep dreaming things that seem random, but then anywhere from a few minutes after I wake up to 20 years later (so far) see it in real life and really have to wonder how that dream ended up being so accurate, especially the fairly repetitive dreams over multiple nights that turn out to be just like a place I am eventually in every day because say I end up working there / in that area and this is complete with details that even when I have gone to some of these places before working there, those details are absent because they haven't been built yet but end up being built by the time I work there or when I am regularly there for another reason. Sometimes it is places I never saw when I had the dream, but then I find myself there regularly. (For example when I was a little kid I dreamt so much that Mission Valley had a trolley going through it that when my mom brought me down there I would ask her where did the trolley go as I started to forget what was persistent dream vs current reality, but then in my late 20's I ended up working in Mission Valley for ~3 years and the trolley ran through right where I remembered seeing it from the dreams and I kept having Deja Vu moments as I could remember looking at things from this view point when I was a kid in my dreams, but now I am seeing it as an adult and it looks just the same complete with the newer constructions I saw in the dreams that just weren't there back then and even from the same perspective that I was standing at that moment. It was like I am right now standing where I was standing in the dream and seeing the exact same things, but how could that be possible if these constructions did not exist when I had that dream? This is just one of many seemingly random examples.) All of this other "brain bending" stuff seems like it is at least outside of the scope of what we can prove near term or outright impossible. Maybe I just want to be proven that I am not that crazy after all. 😉

  • Reply JourneymanHuman January 4, 2020 at 12:38 pm

    We are travelling into the future at a rate of ct, ie our distance in the time dimension of spacetime is (delta t)x(speed of light). This is how all free-fall trajectories in our local gravitational field have the same geodesic, which, as you I'm sure are aware, is what general relativity specifies. For instance, if you throw a ball up into the air and catch it, and then look at the arc described by the photons of a beam of light shot out at the same time (and here we must allow our thought experiment to require a flat plain of one light-second's distance with a constant gravitational field of 1g in order to keep the geometry simple enough to visualize), they might seem completely different, until you add the ct length to the short arc of the travel of the ball, and map both arcs of travel in space and time, whereupon the arc travelled by the ball gets stretched out in the time dimension by the same sort of distance the light beam travels in space in that same time, so now the curvature is the same for both.

  • Reply Musk Mister January 4, 2020 at 1:09 pm

    El. Psy. Kongroo.

  • Reply Andrew Sallans January 4, 2020 at 1:18 pm

    I want to see the universe where sfia is made and ftl is known to be possible XD

  • Reply ALEXANDRE TORRES January 4, 2020 at 1:33 pm

    And what about time travel to the future by relativistic spacetime distortion? I would like to see an episode discussing the easier way to accelerate do near lightspeed WITHOUT going into deep space. Instead of freezing rich corporate people, a company may place then at 99.9999%c speeds on vacuum tunnels, or in orbit or earth, or perhaps somewhere in the inner solar system? how that could be achieved?

  • Reply M January 4, 2020 at 1:34 pm

    This is a good point. If time travel were indeed possible we would likely (especially now with these current events) be seeing travelers from another era. However, just to add, if a group can perfect time travel then they probably would have no problem perfecting concealment tech as well. So even if they were here we likely would have no idea. Maybe they cannot PHYSICALLY be here but can see it in another form. I don't know, all I know is I would love to see those ancient events of speak to someone from another era. But of course it will never happen in my lifetime so ah well.

  • Reply Syn One January 4, 2020 at 2:06 pm

    Would it be possible to put links to the referenced episodes in the description? If it is there and I just missed it, I apologize. Happy 2020 to you.

  • Reply Whiskey Saurr January 4, 2020 at 3:00 pm

    My favorite trope for sci fi time travel, is the consciousness transfer. Like in the show "Travelers." But, then you still might get into the mass issue. Would data be considered mass or weight? Or would it just be rearranged energy?

  • Reply DoleoSeorsum January 4, 2020 at 3:14 pm

    From the study of the works of Lorentz and the recent studies of Relativistic Time Interval theory, I question the link between aging and the arrow of time. So for example if you traveled faster than the speed of light age would reverse, but would the external arrow of time also reverse? Or would the arrow of time continue and you simply grow younger?

  • Reply Jeremy Pace January 4, 2020 at 4:23 pm

    Time viewing appears to be possible (see Vatican and chanting turned into a chrono-viewer), but time travel into the past appears to be not possible. Some UFO abductions seem to take place over hours turned into minutes, or time might be "malleable" for 2-3 days, but then is "set in stone" and the dead past. (I don't count just sleeping to the future as "time travel".) The future is so fluid and ever-changing that seeing the future (for now) does not lead to anything "set in stone".

  • Reply ßerrısırıs January 4, 2020 at 4:52 pm

    Why is there no Time Travelers: The Prime Directive.

  • Reply Benny Macarfy January 4, 2020 at 5:20 pm

    UNIWORS

  • Reply tehbonehead January 4, 2020 at 5:25 pm

    One would wonder…

    How does one resolve the spatial dimensions while traveling through time? Maybe future scientists have given up because they keep sending people back in time, but not updating their position in space…

  • Reply Ben Hubbard January 4, 2020 at 6:17 pm

    Could dark energy be evidence of time travel? Need more space to store material being brought back.

  • Reply Douglas Phillips January 4, 2020 at 6:39 pm

    I was hoping for some mention of the twin paradox, but maybe that's something for another time.

  • Reply whatisbestinlife January 4, 2020 at 6:42 pm

    Photons, gravitons, that travel at light speed don't experience time. So, the entire action/experience/journey/life of these things is happening simultaneously. In its entirety. So a photon isn't a single point, it's where it started, where it ended, and everything in between.

    A real photon then, if you could experience its existence like it does, if you could actually see it as a point of light say, is actually not a point but a long string from start to finish. From end to end. The universe must look quite amazing then to be able to see in this manner, filled with these strings stretching and warping away into the distance and in all directions.

  • Reply CCR W January 4, 2020 at 6:57 pm

    Say, what if you put some sort of crystal device here on earth now and others in different places in the galaxy that could interact? Would the information pass through time zones?

  • Reply Prozacgod January 4, 2020 at 7:11 pm

    I've thought of the idea that maybe time travel is possible, but you just can't travel to any point in space where you can affect your past actions, if I travelled In time and space over 200 billion light years out, my actions could never possibly influence my existence in this universe before I travel.

    I mean not terribly different than some of the alternatives you mentioned, but it has interesting implications.

    Perhaps there is no past moment in the whole of the universe that doesn't influence you, that everything is causally linked. I think that would imply the universe is much much smaller than we realize. (Or something even stranger, at which point Pascal starts to be the better wager)

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