Articles, Blog

Is Time Travel Impossible?

November 19, 2019


If time travel turns out to be possible, I
hereby invite future time travelers to join me on set I’ll post the address one year from today. Okay. Right now. Well that’s a bummer. Time travel stories are cool because both
the past and future are somehow more interesting than the present and because everyone secretly wants a do-over. But so far it appears we are doomed to live
consumed by regret in the eternal, boring present. Time marches on, inexorably and only forward. Or so we thought until Einstein came along. His special and general theories of relativity
changed the way we think about time forever, and believe it or not, their raw equations
permit time travel. They even tell us how to do it. So let’s review the possibilities, and decide
how possible time travel really is. The first approach to time travel uses only
special relativity, which describes how intervals of time and space are stretched or contracted
depending on relative speeds. A fast-moving spaceship appears to experience
a slower rate of time compared to someone waiting back on Earth. Do a trip around the galaxy at close to the
speed of light and very little time might pass from the perspective of the traveler. But they’ll find a minimum of hundreds of
thousands of years have passed when they get back to Earth. However, that’s a one-way trip in time, and is really
just traveling in the same temporal direction at different rates. So the original Planet of the Apes style time
travel is possible. But it’d be nicer to be able to go back
in time. Actually, the math does sort of allow that. The spaceship’s clock slows down as it speeds
up, and it stops completely at the speed of light. And at faster speeds, time should actually
tick backwards. So if you could travel faster than light you
could navigate a path to a point in spacetime before you departed. We saw how to Iconstruct such a path in a
previous challenge episode. Of course we know that the laws of physics
forbid faster than light travel. Or do they? In order for any object with regular mass
to even reach light speed it would need infinite energy – which can never be obtained. But notice I said “regular mass.” We can hack the equations of special relativity
by allowing mass to take values in the weird realm of imaginary or complex numbers. An object with imaginary mass is now restricted
to only traveling FASTER than light, never slower. That means it can only travel backwards in
time, not forwards. We call a particle with imaginary mass a tachyon. If we could control tachyons then perhaps
at least we could send information back in time. But do they exist? Does imaginary mass exist? This is an example where the equations
of a theory technically allow something to be true, but there’s still no good reason
to believe that it is. We’ve seen no evidence of tachyons, and common sense tells us we probably never will. So special relativity isn’t much help. Fortunately we still have the general theory
of relativity, which incorporates special relativity, but also explains the force of
gravity as a result of curvature in the fabric of spacetime due to the presence of mass and
energy. But GR describes a warping of space AND time. So maybe we can warp them enough to take us
back to our own past. The best-known approach is through something
called a wormhole. A wormhole is a particularly bizarre hypothetical
consequence of general relativity. Now, if space can be warped, then perhaps it can
be stretched in such a way as to create a tunnel between two points – and one whose
internal distances could be very short, even if the mouths of the tunnel are far apart. This has the obvious benefit of allowing you
to teleport between distant points in space, but also between distant points in time. This is how you do it: take one stable wormhole
large enough to be traversed. Accelerate one end to close to the speed of
light or drop it into a deep gravity well – its rate of time flow will slow relative
to the other end of the hole. Now bring the two ends back together. They will be offset in time: one portal permanently
stuck in the past of the other by some set interval. Travel through the “future” end
and you’ll exit in the “past.” So this all sounds straightforward enough. But can wormholes even exist? There are a number of ways they might – from
connections between universes in the interiors of black holes to miniscule wormholes appearing
and vanishing on the tiniest scales of space and time. Now, these deserve their own episode. But for now, to build a useful time machine a wormhole has to be large enough to fit through and it has to be stable. The equations of GR do permit large wormholes,
but they are definitely not stable. They collapses on themselves instantly, leaving
inescapable black holes. In order to keep our wormhole time machine
operational, its throat needs to be kept open. We need to counter gravity, and to do that
we need another probably-non-existent form of mass – negative mass – also referred
to as exotic matter. As far as we know, mass can only take on positive,
real values, so a requirement of negative mass seems a non-starter. However there may be hope. Really what we need to open the wormhole
is a negative energy density. Some have argued that we already produce this
in the Casimir effect, in which the energy of the vacuum is lowered between two nearby
conducting plates. However there’s no clear path to translating
this to a large-scale negative energy distribution that could keep a wormhole open. And in fact we’d need entire planets – perhaps entire stars converted to negative energy to do this. Some other time travel options also involve
using negative energy densities – for example the Alcubierre warp drive, which we already
covered. In short – if you have exotic matter you
can probably time travel. But is negative mass-energy as much of a non-starter
as imaginary mass? While the actual equations of general relativity
themselves don’t prohibit it, there are a set of secondary rules in GR that do. These are the so-called energy conditions. They’re a set of requirements that do things
like prevent negative energies and enforce energy conservation. But the energy conditions don’t have a really
fundamental basis, and they’re seen to be violated in some cases – like with the Casimir effect. We can’t completely rule out wormhole or
warp drive time machines based just on the energy conditions. And as it turns out, there may be other ways to build
time machines without either negative or imaginary masses. One example is the Tipler cylinder, conceived
by Frank Tipler based on a solution to the Einstein equations by Willem van Stockum. It’s simple: just build an infinitely long
cylinder of extreme density and set it rotating insanely quickly about its main axis. It will drag spacetime in its vicinity into
a sort of vortex. This generates sub-lightspeed paths through
spacetime that form closed loops, ending up back where they started in both space and
time. We call such paths closed time-like curves. A spaceship traveling along one of these curves
could return to a point in its own past. If you don’t have the budget for an infinitely
long cylinder, you could try building just a very, very long cylinder… and be horribly
disappointed. Stephen Hawking showed that unless the cylinder
is infinitely long this doesn’t work – unless you also modify the spacetime with negative energy. In which case you might as well just build
a wormhole. So it turns out that it’s not so hard to
find solutions in general relativity with closed timelike curves. Kurt Goedel, famous for his incompleteness
theorem, discovered one and he wasn’t even a physicist. His involved an entire universe, rotating
about a central axis and with matter and dark energy perfectly balancing it against collapse
or expansion. So to build this time machine we just need
construct an entire universe – which allows us to travel back in time only within that
universe. Thanks Goedel. Dragging the fabric of space in a circle
can give us our time-loops in very special, and frankly useless cases. Another one is the interior of a rotating
black hole – a so-called Kerr black hole. The maelstrom of spinning spacetime may generate
closed timelike curves deep down below the event horizon. So that’s fun: you can travel back to your
own past, but never to the time before you fell into the black hole, which is probably
the only thing you really want to do at that point. Unless it’s an Interstellar-style black
hole . . . general relativity doesn’t directly refute black hole time machine libraries. Yet. So it seems we have lots of ways to send things
back in time, but it all seem useless for actually making time machines for one reason or another. But the weird thing is that we don’t know
of one consistent, fundamental law in physics that prohibits true time travel. And yet most physicists still think it’s
impossible because time travel threatens the common-sense chain of cause and effect. It threatens causality. Break causality and you can create paradoxes–
time-travel to kill your grandfather and you would ever be born to time travel in the first
place. But there are no true paradoxes – only seeming
paradoxes that point to a gap in our understanding. Stephen Hawking put it nicely with his Chronology
Protection Conjecture. It states that the laws of physics will always
prevent time travel or allow it only when doesn’t cause paradoxes. In other words, the universe has to make sense,
time-travel or no. One way for a closed timelike curve to exist
without causing a paradox is expressed in the Novikov Self-Consistency Principle. Igor Novikov suggested that closed timelike
curves are fine as long as they’re self-consistent. As long as the backwards time-traveling configuration
of matter always leads to exactly to the same forward-traveling configuration. In other words, the loop creates itself. So I don’t know – you try to kill your
grandfather, only to become your own grandfather? Like Fry, let’s not think too hard about
that. An alternative lies in Hugh Everett’s many-worlds
interpretation of quantum mechanics, in which every possible universe exists, splitting
off in an infinite tree. So if you travel back in time and prevent
yourself being born – no problem – your photo doesn’t slowly fade away because you
were still born in that other timeline. Or time-travel could be genuinely impossible. Kip Thorn suggests there should probably be
one fundamental law of physics that prohibits it – for example, the quantum vacuum may
be unstable in the infinitely iterating loops of a closed timelike curves. On the other hand, Kip was the consultant
in Interstellar, so who knows what to believe? In actual fact we can’t know until we have
a full theory of quantum gravity – until then we’re working with the approximate
theories general relativity and quantum theory. Approximate theories can make bad predictions
– like the possibility of time travel. One final argument that time travel is impossible
is that we don’t see time travelers. Stephen Hawking put this to rigorous test
when he organized a cocktail party for time travelers, only advertising the event after
it ended. Tellingly, no one showed up. Though I don’t know – maybe there was a slightly
better party somewhere else in, like, all of history. For now we seem doomed to time travel only
forwards, and very slowly at that. We remain firmly in the grip of that one dimension
that we can never halt nor reverse it’s pace: time.

You Might Also Like

100 Comments

  • Reply Biniam Gaming November 7, 2019 at 12:30 pm

    Not gonna mention endgame’s time travel method?

  • Reply Quantum Fluctuation November 7, 2019 at 5:00 pm

    If we can travel in time, past or future, we do not have free will because everything already written.

  • Reply Jessica Mears November 7, 2019 at 5:00 pm

    Where will the address be posted?

  • Reply André Bazenga November 7, 2019 at 5:01 pm

    What would happen if a spaceship traveling faster than the speed of light, impacted a cosmic body by accident? Big Bang 2.0?

  • Reply Fe Bo November 7, 2019 at 5:02 pm

    It's like we are "falling" through time, since travelling at a certain speed makes it possible to reverse the process. As if time was the fourth dimension of space with its own "gravitational" pull that moves objects at the speed of light. Once you match this speed (in any of the 3 standard space directions) you stop and if you accelerate further you start "soaring" instead of fall.

  • Reply lexalot November 7, 2019 at 5:23 pm

    ah yes
    all we need is an object with imaginary mass
    aka it's possible (in our heads)

  • Reply Aydın Bolat November 7, 2019 at 5:32 pm

    time travel is impossible. thus i will never get back this 13 minutes

  • Reply Tx240 November 7, 2019 at 5:55 pm

    I woke up at 9am. It's now 11:50 am. I traveled through time.

  • Reply nekocatism November 7, 2019 at 10:00 pm

    2:45
    ah, I see PBS are noided. Nice

  • Reply ShakuntalaF November 7, 2019 at 10:13 pm

    How do we know our universe isn't rotating? We have no reference point outside our universe to use to determine. I guess it doesn't matter as much since our universe isn't static.

  • Reply Canzandridas Joe November 7, 2019 at 10:53 pm

    "Is Time Travel Possible?" Well that depends on your understanding of the words "time travel"

  • Reply anubisisbored November 8, 2019 at 3:11 am

    If tachyons can only go back in time. And if all things (atoms, electrons etc.) were created at the same point in time i.e a big bang. Then it would stand to reason that if any such particles ever existed they would never appear in our forward timeline?

  • Reply oicub2 November 8, 2019 at 4:23 am

    Question: Is it possible to travel in, on, or through a light year?
    Answer: probably not so much.

  • Reply Sonicgott November 8, 2019 at 6:59 am

    If areas of high gravity warps spacetime, does that mean that spacetime could also influence gravity?

    “What do we want?”
    “Time travel!”
    “When do we want it?”
    “It’s irrelevant!”

  • Reply Guru Speaks November 8, 2019 at 8:04 am

    At 00:10. The time travelers showed up, but they were wearing green.

  • Reply Raunak Thakur November 8, 2019 at 12:00 pm

    Me : Is time travel possible
    Scientists: Hell yeah
    Me: backward
    Scientists:Hell no you idiot

  • Reply Bodylotion November 8, 2019 at 12:50 pm

    Travelling backwards in time is nothing but Math Porn.

  • Reply M. Harris November 8, 2019 at 6:05 pm

    Your "invitation" to the time traveling community fails to take into consideration the temporal prime directive.

  • Reply paperchasin23 November 8, 2019 at 6:43 pm

    You lost a bunch of weight pussyman. Good job.

  • Reply joe caterman November 8, 2019 at 7:48 pm

    I never heard about Hawking's party…. But now I do know… I'm off to join it!

  • Reply rapierwhip November 8, 2019 at 9:10 pm

    Can we get a 3D graph of 3:42? I mean lets say what we see here but many layers so we can see how gravity affects those lines in a 3D grid rather than 2D grid. All those representations i see are the same using a 2D graph and it really should be 3D for a true visual representation.

  • Reply D0minuZ November 8, 2019 at 11:19 pm

    Going back in time is impossible because it's not about you only, it would be about reverting the state of the whole universe.

  • Reply UltraJeed November 9, 2019 at 7:57 am

    Is it extremely accurate that time is changed dramatically for me if I travel at the speed of light or could that still be refuted? It just sounds really off to me

  • Reply PETECAROLAN November 9, 2019 at 11:52 am

    Say it's 2pm at my location. Its also 2pm 1,000 light years away and every where else. If I travelled to that point 1,ooo light years away and it took me 10 seconds to get there, the time would be 2.00.10pm.
    Travelling back and forth through time is impossible. The equations support the notion but time is the same universally.
    Now if you travel x times faster than the speed of light that would mean that you will get to your destination x times faster but that does not alter the fact that time is a constant every where.

  • Reply Marco Natal November 9, 2019 at 12:43 pm

    Thank you for posting this video. I give it a thumbs up ?. Time travel is not impossible or a theory. You can time travel when you sleeping, but you can't change nothing you could just only Witness what you see. it happened to me in the 80s many times and it still happening to me now and it happens to everybody some will notice some won't. But in the 80s in my dreams my dog got runned over by a white car with two-doors. I was with two of my friends and my mom, when it happened I screamed, then I woke up, it felt so real. I told my mom about it she said it was just a dream. The next day like 8 o'clock he got runned over by a white car with two doors, she was there to witness my dog get killed. After I finished crying, I told her the dream was real. One of the saddest days of my life. PLEASE people keep your dog on the leash.

  • Reply Tech Tacho November 9, 2019 at 3:14 pm

    Time flow is an illusion. Our brains fool us in many ways! Time dilation proves we are in a simulation.

  • Reply Tech Tacho November 9, 2019 at 3:31 pm

    Time travel violates the laws of conservation. If I break a glass cup, pick up all the pieces, melt it down make a new cup and do this over and over again. In order for me to go back in time and experience all those instances of breaking and remaking, all those instances have to be stored, which means adding extra matter/mass as many times. Maybe I’m getting this all wrong, but makes sense to me.

  • Reply VJ Joseph November 9, 2019 at 3:55 pm

    The final argument you made is so incorrect and yet reasonable at this point in time when seen from a general person's view. The whole point of science is to enable us to see what we cant see or feel ,so, just because you havent seen a time traveller doesnt mean you can then announce they cant exist at all in any or your own reality. The second point, is even though approximate theories are flawed at making accurate predictions, thats exactly why they are called approximate because that level of accuracy is only needed. Now, a law made by an observer is not what that governs that reality. Thats another fundamental flaw in understanding. When the knowledge, you have is incomplete and still you want to bias the existing knowledge into thinking that based on the lack of observation it doesnt exist, the reality doesnt bend that much to the bias of the observer. So, you cant lie about time travel which you havent yet discovered and neither can you declare it can or cant exist in your own reality. The lies or speculations or baseless theories doesnt stand for so long into the future that time runs into.

  • Reply David Nuttall November 9, 2019 at 7:00 pm

    I seem to recall that one of the major explanation for the unidirectional flow of time is the Second Law of Thermodynamics: Entropy increases over time. Most other physics formulas do not care about the flow of time; it could go forward or backward, and the formula would deal with it just fine, but going backward through time would require reducing or even resetting entropy to the state it was in earlier in the universe, or at least your local environment.

  • Reply Flying Doggo November 9, 2019 at 7:38 pm

    basically even if time travel was real, it would be extremely dangerous because one wrong move may change the present, or you might go back before you were even born and be erased from existence. this is all just stuff i thought about when i was bored, i recommend just not inventing time travel in the first place, it's too risky.

  • Reply Deependra Pratap Singh November 9, 2019 at 8:14 pm

    If there is something like atom bomb in this world, i therefore want them to donate 1 to me, boom. No one donated me anything, does that mean there is no atom bomb type thing in this world??

  • Reply NoHillary November 9, 2019 at 8:41 pm

    Trump is a time traveler, look it up on internet

  • Reply ironcityblue November 9, 2019 at 11:44 pm

    Yep.

  • Reply Kickin Rocks November 10, 2019 at 1:05 pm

    Ahh. You can't travel back in time, because it would allow you to receive information faster than light. Imagine you start an experiment that requires you to send a beam of light, and wait for it's return. Then a time traveler arrives, the moment the experiment starts, already having the answer.

  • Reply Johnny Murray November 10, 2019 at 2:44 pm

    (Possibility) If time travel was possible it wouldn't matter. After changing one event, from that point on it becomes its own, new time line, with a future completely different and unpredictable. The present can never be altered, the past is the past.

  • Reply Stephen Furr November 10, 2019 at 4:08 pm

    If we ever discover a way, it'll cause a program error in the Simulation we're in and our whole universe sim will get reset! Stop trying to reset the universe! ?

  • Reply Dry Saliva November 10, 2019 at 7:36 pm

    Seems impossible, but who knows maybe it isn't.

  • Reply Marek Hubka November 10, 2019 at 8:20 pm

    Why doesnt we have any quests on our parties for time travelers? Well perhaps, because time travel will be discovered in so far future, that all dates about those parties have been already forgotten. There is not so many people who even know such party has been thrown, and nobody makes sure that the date will not be forgotten, by passing it to their children as a secret they have to keep forever. In few generations no one will even know there have been something like this. I am pretty sure it was not the first party, and propably it wont be even last. Perhaps there will be a party in 2-3 thousand years which actually will have attendants.

  • Reply 54m0h7 November 10, 2019 at 11:47 pm

    Here's a thought experiment combining Time Travel with the Multiverse theories:
    Option 1: Time Travel is possible, and there is only Universe in the Multiverse. Time Travellers would always be in the same timeline, and it would be highly likely we'd see evidence of their travels around historic events, which we don't.
    Option 2: Time Travel is possible, and there are multiple alternate timelines. If the timelines diverge infinitely at every point going into the future then there are infinite futures where Time Travel is invented, and infinite futures where a traveller goes back to the exact same time. This would cause infinite travellers to suddenly appear in the exact same place, which would be infinite mass/energy and destroy the Universe.
    Option 3: Time Travel is possible, there are multiple alternate timelines, but when you travel backwards you never hit your own timeline, rather create a new one. This is the most likely as it solves the other problems. This would however be very bad for Hollywood, as chasing a criminal through time could never be successful as there are timelines where you do and don't catch them.
    Option 4: Time Travel is impossible. 🙁

  • Reply Saul Abrego November 11, 2019 at 1:17 am

    Well if time travel is impossible somebody's got to explain what I just saw a few minutes ago. I was driving up 281 in an area with a lot of construction, now this is at night and there are a lot of barriers along the road. I was passing cars left and right because I drive pretty fast but I saw something that was not normal! A small car somehow passed me I didn't actually pay much attention to it at first but at a stoplight it past an SUV on the right side of it and there were some barriers in the way but somehow it managed to go around this vehicle without hitting the barriers but when I was waiting for it to show up in front of the other vehicle it was gone! It was just gone!! Totally gone!!! disappeared!!!! And by the way I've seen that before a couple of years ago on the highway, and to me that's just too weird. Too much of a coincidence. I wish there was an explanation for it cuz I sure could use it right now!

  • Reply Joseph Fuller November 11, 2019 at 9:59 am

    Dr. Mathew, we did meet on set, but not in the timeline in which this comment was posted…

  • Reply Mca5518a Mca5518a November 11, 2019 at 10:49 am

    Yes, Time Travel is impossible. It will always be impossible. You will never, ever, be able to travel forward, nor backward in time. That's the reality of life.this is it. No Aliens, and no time travel.

  • Reply Ray Kabi November 11, 2019 at 6:21 pm

    Don't forget to post the date!

  • Reply I Miss My Cereal November 11, 2019 at 6:48 pm

    “Whoa…this is heavy.”

  • Reply Mister Scoot November 11, 2019 at 10:26 pm

    Still doubtful that movie style Time Travel is possible….but what is with the joking experiment of inviting time travelers to a party? If it does exist, why bother, if it means altering a time line, or just that no one actually cares? Is it really just a joking thing saying "Haha time travel is improbable".

  • Reply Kenny D. November 12, 2019 at 1:29 am

    Could you build a Tipler Cylinder in a universe with negative curvature?

  • Reply fitnesspoint2006 November 12, 2019 at 4:27 am

    "Everyone secretly wants a do over" couldn't have said it better, time travel every human's fantasy.

  • Reply Brandon Copeland November 12, 2019 at 5:17 am

    you're all simulations and I'm here alone.

  • Reply Swinebagger Hatevirus November 12, 2019 at 7:22 am

    Need a new law? how about Ferengi Rule of Acquisition #217: "You can't free a fish from water."

  • Reply Jaren Williams November 12, 2019 at 8:52 am

    So imagination is time travel. Duh.

  • Reply xnonsuchx November 12, 2019 at 9:02 am

    Theoretical, maybe; Practical, no

  • Reply dom crocitto November 12, 2019 at 11:54 am

    Going into the past is impossible. You’d have to reverse every particle in existence. Faster than light?

  • Reply Rhubarber November 12, 2019 at 12:31 pm

    Why would someone from the future want to party with us? They'll have future interests, future senses of humor, future luxuries, a different language all together. Time traveler's can only come from a time when time travels exists and they may be so far in the future that 2019 is insignificant. If we had time travel today, would we want to party with the medieval kings? Victorian Royalty? No, because their parties would suck. Our common day to day interactions with the internet beat the pants off dark age parties. And even if we showed up we wouldn't be allowed in and a commoner's party wouldn't be recorded. Also they were barbaric by our standards; we will look the same to future peoples and therefore not cool enough to hang out with.

    Everyone says they'd go back in time to kill Hitler, but not Ghengis Kahn, Nero, or Vlad the impaler, why? They're old news and possibly responsible for our modern timeline to exist. Time softened the horror. In a hundred years Hitler will be seen as another tyrant whose threat spurred along technology and humanity's self awareness. He won't be evil anymore, not more than any other awful historical figure.

    Time traveler's would travel back to solve their own timeline, or having time travel in their possession have a greater understanding and therefore know not to abuse it, or share it to less evolved forms of their species. We might be too monkey-brained, too emotional, illogical, or tribal to trust this technology with. "Fixing the timeline" will mean something different to every individual and some of that could be hateful.

  • Reply james bailey November 12, 2019 at 9:18 pm

    UFOs are time travellers

  • Reply komnishura November 12, 2019 at 9:50 pm

    Well, when and where is this recorded? I managed to travel back in time but could not find the address of the studio..

  • Reply john lacey November 12, 2019 at 10:16 pm

    Why does everyone use the argument "Where are the time travellers", surely they wouldn't want to interact. Hell, maybe UFO's are humans from the future.

  • Reply Qodus November 12, 2019 at 11:10 pm

    How do we know you posted the address?

  • Reply TZ November 13, 2019 at 7:31 am

    El Psy Congroo…

  • Reply Tim Vroomans November 13, 2019 at 10:24 am

    …, nor halt itS PACE: TIME

    Well played

  • Reply philippe roure November 13, 2019 at 11:12 am

    Time travels do exist because otherwise noteworthy non-linear Hollywood scenarios wouldn't be possible in this universe.

  • Reply GreensOplenty November 13, 2019 at 12:04 pm

    could you send particles or something back threw time and hit someone in the head and make em see/mimic a picture or hear a noise?

  • Reply Gino Foogle November 13, 2019 at 1:12 pm

    "Time" is a fabrication of man. And even if we could travel at the speed of light you are still not time traveling.

  • Reply Guilherme Pacanaro November 13, 2019 at 3:17 pm

    So…. We just need to build a small universe, 2m diameter, solved.
    Hahahah

  • Reply MGTOW Lawyer November 13, 2019 at 7:50 pm

    what if you travel so far into the future you end up in the past? lol

  • Reply utley November 13, 2019 at 8:02 pm

    Is time travel possible? Yes. I believe you can only travel backwards in time and not forward in time. The future doesnt exist; the past has existed. You cant travel to a place that doesnt exist yet, but if it has been made it cannot be un-made. The past you travel to will cease to be the past of your future because its no longer the original past. You just move to a new reality where that new future exists only because you now belong there; the timeline you just left no longer exists and has only existed for that new timeline to exist.

  • Reply Millie Kelly November 13, 2019 at 9:22 pm

    Look can I or can I not go back to the 90s and marry a young leonardo dicaprio that’s what I’m here for

  • Reply Alexandre Yuri November 13, 2019 at 11:09 pm

    Perhaps time travel is possible but mankind never lives long enough to achieve such a milestone

  • Reply michael hall November 13, 2019 at 11:11 pm

    I’ll not say too much, but it’s within us snd a great topic. Keep posting

  • Reply Yvonne C November 14, 2019 at 1:23 am

    Who's here in 2040

  • Reply Dean Batha November 14, 2019 at 3:27 am

    Time travel is possible. I traveled 13 minutes into the future while watching this episode.

  • Reply Michael Chigano November 14, 2019 at 5:30 am

    Time travelers probly siting back looking at this and laughing lmao

  • Reply ChrisC November 14, 2019 at 6:17 am

    I don't secretly want a do-over.

    I LOUDLY want a do-over.

  • Reply Lee Parker November 14, 2019 at 6:58 am

    You forgot to Actully post the address a year from now lol

  • Reply Fraser M November 14, 2019 at 8:08 am

    time travel backwards seems only possible if you can visit different regions of space without having to travel, then back. travel needs to be cheated somehow. a major glitch. might be beyond us. these glitches may exist (we know nothing about blackholes, etc) but we'll probable never be able to tap into them.

  • Reply Rorschach Daws November 14, 2019 at 11:04 am

    Yes it's possible

  • Reply Jeong-hun Sin November 14, 2019 at 3:36 pm

    I'll save you 13 minutes.
    The answer is "Negative".

  • Reply Robert Gamble November 14, 2019 at 4:36 pm

    I am traveling through time every moment. I am always here, and it is always now, so by the time I press the send button, I will not be where, or when I was.

  • Reply lucky loki 07 November 14, 2019 at 11:52 pm

    Here’s the thing time travel can be proven to not exist here’s how I’ll come back to this time When time travel is invented therefore within the time of your life there will not be time travel the average life span of a human is 80 yrs

  • Reply Dustdepo November 15, 2019 at 4:36 am

    I DONT GET IT
    NOW HIT THE LIKE BUTTON

  • Reply ____________________ November 15, 2019 at 11:18 am

    I checked the address you posted; and yes, I got the joke!

  • Reply Billy Mcnomates November 15, 2019 at 4:11 pm

    All of us are time travellers relative to each other some are ahead some are behind but where is the reference?. Why did he not include entanglement ?

  • Reply Chris Kamper November 15, 2019 at 8:37 pm

    Time travel to the past would break matter-energy conservation, because it would add the mass (which is energy) of the time traveller to the Universe.

    Even if it didn't: this also precludes the grandfather-paradoxon – there is no such a thing, time would simply go on without your original self being born but you would be there.

  • Reply Jethro Games November 16, 2019 at 10:00 am

    "Time travel" impossible. I say it would be more like "Sliders" and univers hopping….

  • Reply FortNikitaBullion November 16, 2019 at 4:53 pm

    I'll settle for fast-forward only travel. I could just put a few bucks in the bank and travel a few thousand years into the future and come out a billionaire. Or if I see a girl I like but she's too young I could remedy that too.

  • Reply Sean Heupel November 17, 2019 at 12:30 am

    THEORY: Assuming we could contain internal inertia (i.e. being flattened to the atomic level due to acceleration), then essentially stacking rail guns could push us faster than light (i.e. a rail gun launching, then another rail gun theoretically doing the same). Do that 3 times over, and it is possible, assuming physics don't change. You're welcome.

  • Reply Joan Enrique Torre Pinares November 17, 2019 at 9:55 am

    Time travel is imposible, for the simple reason that time doesn't even exists. What we call time is actually movement, and in the theorical experiment of the planet of the apes one thing that is not in account is that earth will still be moving, and it's "future" is not located in the same place, but in the place where its movement will take the planet. So, no matter how "fast" you can travel, the movement of earth won't go faster. Come on guys, time is concept that abstracts movement and is useful for mathematical models and for applied physics, but you can't explain reality with a fiction.

  • Reply aspektx November 17, 2019 at 10:36 am

    If there is a president of the United States I hereby invite them to come visit me.

    I'll keep you all informed as to the results.

  • Reply Messerschmitt Mustang November 17, 2019 at 3:14 pm

    The conclusion: time travel is currently impossible

  • Reply Fadli Amir November 17, 2019 at 8:09 pm

    this is what we call as hope… that is the reason why god create limit to every living thing and logic behind its limitation… u try to cross that limit u will end up crazy… just be normal dude and accept what u have now.and move on…

  • Reply bob smoth November 17, 2019 at 11:07 pm

    If I had a time machine with cargo capabilities, I could go back in time to the dump and make a living from E Bay

  • Reply teddy devereux November 17, 2019 at 11:43 pm

    Is time travel possible?
    Yes, if we keep talking about it but if you actually want to do it then, no.

  • Reply Peter Storms November 18, 2019 at 3:16 am

    Removing that sign Authorized Personnel Only might have helped

  • Reply Kevin Reardon November 18, 2019 at 4:21 am

    There was a better party to go to. And if you send out an invite like that again, make sure you have crumpets. Just showing up to prove you right is not enough motivation.

  • Reply Depzei November 18, 2019 at 7:07 am

    Yes I’m from 99999. I time traveled to this time because that’s when my ps4 account gets unbanned.

  • Reply khatack November 18, 2019 at 10:36 am

    You've got a dead block in the video that can bee seen around 8:31–8:33

  • Reply Who’s There? November 18, 2019 at 5:22 pm

    Not possible.
    I hate this theory. It’s the same theory that lumps in the spaceship clock nonsense and also says if you go the speed of light somewhere and come back your friends and family will have aged while you haven’t.
    Now let’s say the human body can survive that speed… you are ASSUMING that your body’s biological aging and comprehension slows down just because it is moving light speed. The object (ship and human) are moving light speed not the whole existence outside of it. It does not make sense because it is nonsense.
    Is light speed possible? It could be.
    But it has no effect on universal time.

  • Reply MilesUmbrae November 18, 2019 at 7:19 pm

    I must be the odd-one-out .. because I'm not really interested in "do-overs", but rather to confirm historical events and to keep accurate historic records.

  • Reply William Hinliz November 18, 2019 at 11:19 pm

    Time travel is impossible because you won’t be able to travel to a universe before it was formed. There will be a limit on how far back you can travel. Also because the universe is expanding you might travel in time just to find yourself in a different part of the universe where the earth hasn’t arrived yet.
    So you must know the exact location and the exact time where you are going to travel.

  • Reply Gary Hawkins November 19, 2019 at 6:36 am

    Not to soil the carpet but one of my favorite sayings is, God would drop dead of boredom if the future is known.
    Try replacing imaginary numbers with the life energy Wilhelm Reich was killed for reporting on. Same: Ether = Higgs Boson and it attempts to conglomerate to higher concentrations of itself, which explains how God came to be, to some degree. My people mathematicians perish are losing their marbles for lack of knowledge.

  • Reply Hygor Sandrews November 19, 2019 at 4:08 pm

    Is time travel possible?
    PBS: yes, but no

  • Leave a Reply