00:00You may have time traveled multiple times already.
00:05You just don't remember it.
00:07A recent study says that all your memories of the trip would be completely erased as soon as you're back in the present.
00:13And you can blame it on something called entropy.
00:16To explain it, we first need to talk about closed time-like curves, or CTC.
00:21This is a closed path where a particle could travel, and it ends up right back at its starting point, at the exact same time it left.
00:30In other words, it's like a cosmic time loop.
00:35Take this notebook paper.
00:37Picture each line as a different timeline with a beginning, a middle, and an end.
00:42Now if you roll that sheet of paper, the lines connect.
00:45Suddenly they form a continuous line with no beginning or end.
00:49That's what CTCs are.
00:51Closed timelines that don't have a starting point.
00:55Past and present blend together in an internal time loop.
01:00Now, a more practical example.
01:03You're taking a walk around a park.
01:05A woman jogs past you, and a dog starts barking.
01:09You keep walking, but then, wait a minute.
01:12You realize you're back at the exact spot where you started.
01:15The same woman jogs by, and the dog barks again.
01:18But here's the thing.
01:22It's not just that you've returned to the physical starting point of your walk.
01:26In a closed time-like curve, you're retracing not only your steps, but every single second of reality itself.
01:34All right, now think about the big moments in your life.
01:38Being born, graduating from college, getting married.
01:42If all these events are part of one big time loop, that means time travel is possible.
01:48It sounds crazy, but there's a concept behind it called the self-consistency principle.
01:53It says that time travelers can't create time paradoxes.
01:58I mean, time travel can't just be this wild, chaotic mess like those crazy butterfly effect scenarios.
02:05Even if you go back in time, everything in your life still has to fit together in a way that makes sense
02:10and lines up with what we already know today.
02:13I'll explain.
02:16Let's say you go back in time and stop your mom from meeting your dad.
02:20But here's the problem.
02:21If they never meet, then you wouldn't exist.
02:24And if you don't exist, how could you have gotten into the time machine in the first place?
02:30That's a time paradox.
02:33That's why time travel could only work within these closed time-like curves.
02:37No matter what you do, the past, present, and future are locked in.
02:42They're always going to play out the same way, like a loop.
02:47Okay, so now you understand what CTCs are and why they're important for time travel to make sense.
02:54Now, we can finally talk about entropy and why it's probably the reason we'd lose our memory after a trip to the past.
03:02Entropy is a way to talk about disorder, chaos, or randomness in a system.
03:07Imagine a super clean, minimalist bedroom where everything is neatly arranged.
03:13Everything's in order.
03:14That's low entropy.
03:16But then, picture a messy teenager moving in.
03:19Every day, clothes, books, and random stuff gets scattered around the room.
03:24It's a mess.
03:25That's high entropy.
03:26In nature, things usually trend toward more disorder unless you actively work to keep them organized.
03:33Like this ice cube.
03:35It's made up of water molecules, all neatly lined up in perfect order.
03:39Low entropy.
03:41But if you take this ice cube out of the freezer, it will melt into water.
03:45See how the puddle looks messier now?
03:47In this form, the water molecules can be arranged in so many different ways.
03:52They're all disordered and random.
03:54And that's higher entropy.
03:57If we apply this idea to time travel within a CTC, the closed time loop, things get even more interesting.
04:05According to specialists, a key feature of this circular journey is that the level of entropy has to be the same at both the beginning and the end of the trip.
04:13Here's an example.
04:15You're just living your everyday life.
04:17Nothing too exciting going on, so the entropy level is low.
04:20But then, you get inside a time machine and go back to the past, right before you broke up with your high school sweetheart.
04:28By traveling through time, the chance of you changing the past and totally throwing your story into chaos is pretty high.
04:35Let's say you don't break up with her, and in this second chance, you decide to propose to her.
04:41See how everything could go totally sideways, right?
04:44So, when you go back to the past, the entropy is at a super high level.
04:48Now, you get to the exact moment when you're about to talk to your past love.
04:54At that point, entropy is at its peak.
04:58You're about to kneel down, show her the engagement ring, when, well, here comes the self-consistency principle, and it throws a cold bucket of water on this whole romantic idea.
05:08Remember, in a closed time-like curve, nothing can significantly change the present reality.
05:16All the changes a time traveler makes in the past can't cause any historical paradoxes.
05:22So, sorry to say, but you're not going to end up with her anyway.
05:27You decide to hop back into the time machine and return to the present.
05:30You get back into your routine, your job, and, well, your single life.
05:36After completing the time loop, your timeline is back in order.
05:40Now, the level of entropy is low again, just like it was at the beginning of your journey.
05:45It's like you did a reset on the system.
05:48And that's the bad side effect of all this.
05:51Pressing this reset button would probably erase all your memories of the trip by the time you get back to the present time.
05:59Unlike in the movies, a time traveler probably won't recall anything.
06:04What?
06:05Now, answer in the comments.
06:07Even if you can't remember what you did after going back to the past, would you still take the risk?
06:13I'm guessing your answer would be, yeah, of course.
06:16That would be my answer, too.
06:18After all, we could bring our phones and still make tons of cool photos on this trip, right?
06:24Well, no.
06:26This is where the laws of physics crush our hopes.
06:28Again.
06:30The second law of thermodynamics says that in an isolated system, entropy or disorder tends to increase over time.
06:38But this doesn't apply only to humans, but also to non-living things.
06:43It's why you can't unscramble an egg, unmix coffee from milk, or take your phone into a time machine.
06:51If a time traveler stores any data on their smartphone during their journey, experts believe it will probably get wiped out as soon as the trip ends.
07:00All the videos, photos, poof, gone.
07:03That's because machines probably wouldn't work properly when we go back in time.
07:09For example, let's say you bring a classic analog watch with you.
07:13For all the reasons we've already talked about, when you come back to the present, the clock needs to be exactly where it left off.
07:21I mean, the clock hands should be in exactly the same position at the beginning and the end of your journey.
07:28But to make that happen, it's likely that the frequency and number of ticks during the trip will be different.
07:35That could cause small problems in clocks made for regular time, making them unreliable.
07:40Something similar could happen with your phone.
07:43Its system probably wouldn't work as it should.
07:45All these consequences of time travel were described in a study by a mathematician, published in 2024.
07:53While his theory doesn't determine whether time travel is actually possible,
07:58it does point out the strict conditions that would have to be met.
08:03And, well, it seems like having a time machine at home might not be as great as it sounds.
08:08In the end, you wouldn't remember a single thing about your amazing trip,
08:14and you'd probably just end up exactly where you are.
08:19That's it for today.
08:20So, hey, if you pacified your curiosity, then give the video a like and share it with your friends.
08:25Or, if you want more, just click on these videos and stay on the bright side.
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