00:00 Okay, so you've seen the movies and read the books on time travel.
00:04 Most of them tell stories about entering some futuristic boxes, and in the blink of an eye,
00:09 you're in some different epic.
00:12 For now, this is just sci-fi.
00:14 But there are ways to make time travel possible, at least theoretically.
00:19 We just don't have the technology figured out yet.
00:22 For starters, time travel to the future could be achieved by traveling at high speeds, but
00:28 not just getting a ticket on the superhighway kind of speed.
00:31 This is based on Einstein's theory of special relativity.
00:35 It explains that time slows down for objects that move at really high speeds.
00:40 And the good news is scientists have already tested this theory, and it looks promising.
00:45 They did it with the help of two identical clocks.
00:48 One was placed on a jet, and one stayed on the ground.
00:51 They found that the clock on the jet ticked slower than the one on the ground because
00:55 of how fast the jet was moving.
00:58 The faster an object is moving, the more time will slow down for it.
01:02 Currently, the fastest speeds achieved by human technology are seen in a special type
01:06 of particles called neutrinos.
01:09 Some of these can move at almost the speed of light.
01:12 At these speeds, 1 second for the protons is equal to 11 months for us.
01:18 We might be able to time travel to the future with the use of gravity, too.
01:22 This idea is based on Einstein's findings, namely, his theory of general relativity.
01:28 This theory explains that the stronger gravity is, the more slowly time moves.
01:33 This means that as you get closer to the center of the Earth, the strength of gravity increases.
01:38 And if you think about it like that, time actually passes more slowly for your feet
01:43 than for your head.
01:44 Now, is that why I'm always late for stuff?
01:46 Good excuse!
01:48 This effect has been measured, too, with the help of the same strategy with two identical
01:53 clocks.
01:54 Scientists placed them on shelves at different heights and measured the rate of ticking.
01:58 The clock on the lower shelf ticked more slowly because it experienced a slightly stronger
02:04 gravity.
02:05 But this option comes with a catch.
02:06 To be able to travel to the far future, you'll need to find a place with extremely strong
02:11 gravity, like a black hole.
02:13 That's a point in space where the gravity has so much force that even light cannot escape
02:18 it.
02:19 There, gravity becomes so intense that matter gets squeezed into a tiny space.
02:23 The closer you get to the black hole, the more slowly time moves.
02:27 However, traveling via a black hole is very dangerous.
02:31 Mostly because it's a one-way ticket.
02:34 Once you cross its edges, there's no coming back.
02:36 Now, here's a fun fact.
02:38 The GPS systems we use on our phones and in our cars already have to account for time
02:43 dilation effects in order to work properly.
02:46 That's because of the speed of the satellites they use and the gravity they feel here on
02:51 Earth.
02:52 Without these corrections, your phone's GPS wouldn't be able to pinpoint your location
02:56 on Earth very precisely.
02:58 Meanwhile, the third option has less to do with the universe's unknown forces and more
03:03 to do with our own bodies.
03:06 Scientists are trying to find ways to time travel to the future by slowing down the body's
03:10 own processes.
03:11 It's not "time travel" per se.
03:14 You wouldn't technically be going anywhere.
03:16 But if your body stays put for a long period of time, you could eventually wake up in the
03:22 future.
03:23 Some animals, like bears and squirrels, can slow down their metabolism during hibernation,
03:28 which means they don't need as much food and oxygen to survive.
03:32 Specialists are trying to figure out if humans can do the same thing.
03:36 They're working on ways to make people go into a short-term hibernation for a few hours
03:41 to begin with.
03:42 This could be helpful for medical emergencies too, in order to help a person before they
03:47 can safely get to the hospital.
03:49 In 2005, scientists were able to slow down the metabolism of mice by exposing them to
03:55 a small amount of special gas.
03:57 However, when they tried to do the same thing with larger animals, it did not work as effectively.
04:04 Our fourth option of traveling through time is really unique.
04:07 It involves a special type of shortcut that may exist in our universe called wormholes.
04:14 Before we move on, let's try to understand what they are.
04:17 You'll need to picture two balls and a trampoline.
04:20 If there's no pressure applied on the trampoline, it stays flat.
04:24 Now imagine the two balls placed on the trampoline symmetrically.
04:28 If you look at them from this perspective, there's no possibility of them ever touching.
04:33 But if you put enough pressure on the trampoline between the two balls, this flexible fabric
04:38 can stretch so much that the two objects might potentially touch each other.
04:42 The same thing happens with stars in different star systems.
04:45 They're big enough to curve space around them.
04:48 That's why most planets tend to orbit around a star.
04:51 The tunnel between those two points would be a wormhole.
04:55 These wormholes could be used to travel long distances, like a billion light-years, or
04:59 even visit different times.
05:02 Many scientists, like Stephen Hawking, think that wormholes might appear and disappear
05:07 but be very small – smaller than atoms.
05:10 The problem is that we don't know how to catch one and make it bigger so that people
05:14 can use it.
05:15 This would take a lot of energy, and we don't know if it's even possible.
05:20 Some astronomers say that even if we could find a wormhole and enter it, it would rapidly
05:25 collapse on itself.
05:27 Even the tiniest bit of extra mass, like that of our bodies, for example, can result in
05:32 the wormhole slamming shut, like a rubber band that's been stretched too much.
05:36 Now, the fifth solution for time traveling was proposed by an American physicist named
05:41 Ron Mallett.
05:43 It involves one resource that we know for sure is abundant in the universe – light.
05:49 The scientist proposed a theory about time travel that would use a rotating cylinder
05:53 of light.
05:54 He believes that if something was dropped inside this swirling cylinder, it could be
05:59 moved in both space and time, similar to how a bubble moves when you swirl it with a spoon
06:04 in your coffee.
06:06 According to Mallett, the right shape of the cylinder could allow for traveling to both
06:10 the past and the future.
06:12 The physicist has been trying to raise money for an experiment to test his theory.
06:16 This experiment involves dropping tiny particles, called neutrons, through a circular arrangement
06:21 of spinning lasers.
06:23 However, other scientists say Mallett's theory is impossible, and there's no need
06:27 to test it further.
06:29 Well, even if we eventually figured out a way to travel back in the past or to the future,
06:34 would it be safe?
06:36 Scientists have been talking about a problem called the paradox of time travel for a long
06:41 time.
06:42 The main question is what would happen if you went back in time and did something that
06:45 changed the future.
06:47 However, a new study from researchers from the University of Queensland says that this
06:52 problem might not be real after all.
06:55 The scientists have done some calculations and found out that even if you had changed
06:59 something in the past, the timeline would still end up the same way.
07:04 Another variation of this problem is called the grandfather paradox.
07:08 Imagine going back in time and preventing your own grandfather from having offspring.
07:13 Come to think of it, it automatically means you shouldn't exist in the first place.
07:18 If your grandparents didn't have your parents, how can you exist at all?
07:22 Well, these days scientists are certain that even if you did experience something like
07:26 that, you'd still exist in the present.
07:28 That's because the timeline that already exists has a way of adjusting itself, regardless
07:34 of where people are in time and what they do.
07:38 Or somehow get 1.21 gigawatts in a DeLorean and make like Marty McFly.
07:44 That's it for today!
07:47 So hey, if you pacified your curiosity, then give the video a like and share it with your
07:51 friends!
07:52 Or if you want more, just click on these videos and stay on the Bright Side!
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