Today we're going to talk a little bit more technically about what exactly is time like if we're going to travel through it we probably should know what it is right we're also going to talk about whether or not time travel is going to be possible and the consequences of what would happen if we travel through time and whether we've already time traveled there's a lot to talk about that's why we have four episodes this week which I'm super excited about but today first let's talk about whether time travel is possible so if you're going to travel on something or through something or whatever kind of the first step is knowing what it is if
I'm a build a boat to sail on a lake I probably need to understand water so
BayaneBartar.org that's what we're talking about and the problem with time travel is we don't really have a lot of definition of what time is because to be honest a minute a second an hour days it's all relative depending on what planet you're on and depending on your experience we invented the idea of time time is our perception of things right it's how we divide ourselves in our lives in our you know days but all of that is completely relative so what is time on a bigger question needs to be answered before we can travel through it and many people have been trying to answer this for a long long time and there are so many aspects to think about when considering time or explaining time but where I always start is the super simple easy to understand second law of thermodynamics
I'm sure I don't have to tell you guys the first law of thermodynamics you've all heard matter and energy cannot be created or destroyed so the quantity of
BayaneBartar.org energy in the universe does not change ezpz second law of thermodynamics states that as energy is transferred or transformed more and more of that energy is wasted so this deals with the quality of energy in the universe is how we try and put it into perspective it also says that it's natural and basically unavoidable for every isolated system to slowly duvall into entropy entropy is a fancy science word it's very difficult to explain it with accuracy but basically what we mean is disorder or chaos again though it's more complicated than that so this is important when talking about time because the second law of thermodynamics gives us the arrow of time if systems slowly devolve into entropy and they never go back they never become less and tropic that means there must be only one way that time can move it must move along this arrow of increasing entropy low entropy is more orderly high entropy
BayaneBartar.org is more disorderly this is of course all the way to the heat death of the universe everything's so entropic that it's over it's done so this gives us that arrow of time but we didn't always think this way about time for centuries all of the most brilliant minds believed the universe it was static it was infinite time was constant throughout the universe it was no different on Mars or Jupiter than it is here on earth of course at the time we didn't know that the universe was actually expanding this is proven now to be the case and we also now know how old the universe is it's roughly 13.8 billion years but this all started with
Ma Swain Einstein and his theories of relativity you may have heard about this covered it pretty exhaustively in our light series but if you haven't tuned into that yet because I'm sure you're going to after this will give you a
BayaneBartar.org refresher how's that sound essentially the speed of light is independent of the motion of the observer is measuring the speed so what does that mean let's say you're measuring the speed of a car passing you it's going to seem like it's going faster if you're just sitting still watching it but if you are in another car it's going to seem like it's going slower driving alongside it right the speed of light is constant no matter what that's pretty much what equals mc‐squared it's constant the speed of light is constant and this is what
Albert Einstein thought of in 1905 and it's known as special relativity but it didn't tell the whole story because it only took into account the constant speed of light and not what happens to things accelerating or decelerating also gravity this is where the theory of general relativity comes in with bit of that special relativity as well
BayaneBartar.org and it changed our perception of gravity completely gravity wasn't just a force essentially acting on two objects but a warp of space‐time by a massive object like a planet or a star still with me here good think of it as a piece of fabric stretched out that fabric is called space‐time now that fabric is also four‐dimensional it's not three‐dimensional its four‐dimensional that's complicated but think of it as fabric right put a bowling ball in the middle of a bedsheet and makes that curving motion toward the bowling ball it's a bigger warp with a bowling ball than a baseball right so according to
Einstein's theory of general and special relativity x' that is how gravity works things with more mass warp space‐time more so time is essentially what we mean by the fourth dimension so if you have length and width and Heights you know the z axis and the y axis and the x axis time gives us a direction and
BayaneBartar.org gravity can bend that fourth dimension it can bend time now PhD students in physics I know I know the fourth dimension is not technically time it's way more complicated than that I know that I get it second law of thermodynamics I'm with you I understand we're just trying to comprehend this ok this is tough stuff anyway back to the story so we've proved that this is pretty much how the universe works and time moves slower relative to gravity and also speed if you're still with me let me put it all in perspective if you are T LDL too long didn't listen don't worry about it time is actually moving slower for things that are moving faster so a satellite above the earth that say carries a GPS thing those GPS equipments have clocks on board very very accurate clocks and they have to fix those clocks all the time the reason they have to do that is because we are experiencing more gravity
BayaneBartar.org here on the ground and so are our clocks we're also moving slower so relative to us GPS satellites have a different experience of time about 7200 nanoseconds every day so they have to fix it this is known as time dilation and if we didn't understand general relativity and special relativity we wouldn't be able to fix GPS and you wouldn't be able to know where the nearest restaurant is and that crazy man that guy in stein swain for sure so
Einstein's theories of special and general relativity essentially showed that time travel could be possible because of the way gravity bends space‐time in 1935 Einstein teamed up with Nathan Rosen and created the idea of a wormhole people who are really excited on the bus right now listening to this yes we're going there the einstein‐rosen bridge it's theoretical and what most people would call a wormhole it's a passage or a bridge
BayaneBartar.org through space‐time think of it like two mouths at different points in time right or think of it like a piece of paper that you fold over and stick a pencil through the pencil makes a hole to two different points in the paper and that is now the wormhole the math of
Einstein's theory of general relativity actually proves that wormholes can exist they can happen but of course we've never found one the math also shows the mouth of a wormhole could be a black hole check out our black hole series super awesome but black holes are not wormholes and don't go spreading that around it's based on negative mass don't worry about it anyway wormholes are very unstable but they could potentially have time travel as part of the deal a theoretical physicist at Caltech Kip
Thorne hypothesized that wormholes could also be time machines it require us to manipulate that wormhole and we're not
BayaneBartar.org quite there yet it would require an amazing amount of energy loveyou stargate sg1 for also talking about this but the einstein‐rosen bridge isn't the only theory of time travel if you combine it with Kip Thorne's idea of manipulating it there are other theories as well and they're pretty insane for example one you may not have heard of is called the Tipler cylinder and it came from the mind of an astronomer named
Frank Tipler and it is super interesting although Frank men what the heck this is crazy so imagine a cylinder let's put it in space because that's easier right it's made out of a material ten times the mass of the Sun and it spins on a vertical axis but like really really really really fast a few billion revolutions per minute which would create a frame dragging effect I don't understand exactly what that is but you can ask Tipler about it Tipler says that
BayaneBartar.org any ship that followed a course around the cylinder would be in a closed timelike curve because of the way that cylinder and it's very high mass would be affecting gravity the closed timelike curve he abbreviated as a CTC so when it comes out of that course around the CTC it would be years in the future but they could also possibly be galaxies away there are a bunch of things wrong with this theory no offense Tipler the cylinder would have to be infinitely long and weird stuff would happen toward the bottom and the top of the cylinder and the ship would have to steer clear of all of that and the theory came out in 1974 which probably surprises no one
LSD very popular around that time anyway there's also another theory of cosmic strings it's another time‐travel theory think of narrow tubes of energy that stretched the entire length of the universe they'd have such crazy amounts of mass
BayaneBartar.org that they would warp space‐time again based on mass gravity and the space‐time connection if these two bad boys ran parallel to each other some theorize that could make time travel possible there'd be so much gravity there I'm not going to try and explain it because I don't fully understand it myself but it's super neat but of course there's also the most popular one in fiction and that is the actual time machine like a machine however there are people who are thinking about how this could be done in real life a real time machine now it gets kind of funky so stick with me as we mentioned earlier the Tipler cylinder is the closed timelike curve or CTC and you need that to travel through time it's one way to do it right easy‐peasy so to create this without an infinitely long cylinder that spends billions of times per second with the Sun and all of the mass and all of whatever you could do this smaller think of a doughnut
BayaneBartar.org shaped hole inside of a sphere made up of normal matter so like I don't know metal or something inside of that hole space‐time could be bent on itself with gravitational fields okay if you can manipulate gravitational fields to such a degree that you can create enough gravity that would form a closed timelike curve so to travel back in time a person would just need to run around inside of this doughnut shaped thing and somehow it would take them back in time I'm not sure that I even completely understand list why can't we just fly a Klingon bird‐of‐prey around the Sun can we just do that I'd be great
Star Trek for look there are a lot of theories on how time travel could be possible outside of of course Doc
Brown's patented flux capacitor but we may need to stop here because my brain hurts all right I just really need to stop for now.
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