00:00We've all thought about rewinding time, whether to fix that cringeworthy mistake or a sneak peek at next week's sports scores.
00:09But let's be real, those thoughts fade.
00:12For most of us, time travel is just a fun movie idea.
00:15But for astrophysicists, time travel isn't just sci-fi.
00:20It's a serious puzzle hidden in the fabric of space-time.
00:23And now, new models suggest the universe might just allow time to bend in ways that didn't seem possible.
00:32Humans were intrigued with manipulating time long before complex scientific models.
00:39In an ancient Hindu story, a king visits the heavens for minutes and returns centuries later.
00:45In a Japanese legend, a fisherman spends days in an underwater palace and comes back to find generations have passed.
00:53These are some of the myths that hint that time doesn't flow the same everywhere.
00:59And time traveling as a concept didn't just pop up from regret or curiosity.
01:03It also came from watching space.
01:06Time feels like one constant in our lives.
01:09It's always moving forward like a river.
01:12It flows forward, and it's predictable.
01:14But when we zoom out, way, way outside of our planet, it's a different story.
01:20To physicists, time bends, stretches, and slows down depending on how fast you move or how strong the pull of gravity is.
01:30And that's not just a theory.
01:31It's measurable, proven, and built into the technology we use every day.
01:36For example, astronauts on the ISS orbit Earth at 17,000 miles per hour.
01:42And their clocks tick just a tiny bit more slowly than ours.
01:47It's only milliseconds, but technically, they've aged less.
01:51You can see this effect in your everyday GPS as well.
01:55Satellites up there feel less gravity, so their clocks tick a bit faster.
02:00Imagine playing a racing game where your car and your controller are a bit out of sync.
02:05That's why GPS needs constant tweaks, or else your phone would think you are miles away.
02:13Gravity also messes with time.
02:16Scientists proved it using two atomic clocks.
02:20Atomic clocks are like the ultimate devices that measure time.
02:24They don't tick with gears or crystals.
02:26They tick with atoms, the universe's own metronomes.
02:30One clock was on a skyscraper roof, the other closer to the ground.
02:36The lower one, feeling stronger gravity, ticked just a tad more slowly.
02:41The difference was tiny, but it proved that even height can tweak time.
02:45Now picture being near a black hole, where minutes could equal years elsewhere.
02:50This might help you get those mind-bending scenes from interstellar.
02:55So yes, time bends, and scientists know this.
02:59And the challenge now is learning how to do it on purpose.
03:04Einstein's work proved that time could move differently for different observers.
03:08The faster you move, the more slowly time passes for you.
03:12This phenomenon is called time dilation.
03:15Think of Marvel's comic Flash.
03:18He runs incredibly fast, but he doesn't really slow the world down.
03:22His own clock runs more slowly, so to him, everything else looks frozen.
03:27If you could reach the speed of light, your time would almost stop entirely, while the rest of the universe would keep racing ahead.
03:36For decades, physicists believed that was the only path to real-time travel.
03:41But the Flash is a superhero, and Einstein proved that nothing with mass could reach that speed.
03:47The faster you go, the heavier you become, and the more energy it takes to keep accelerating.
03:53To actually reach light speed, you'd need infinite energy, because your mass would become infinite too.
04:00Since infinite energy doesn't exist in the universe, it's physically impossible.
04:04That's why physicists started asking questions like,
04:08If time can stretch and bend, could it also fold?
04:12In 1994, physicist Miguel Alcubierre posed a question.
04:18Could Einstein's math let us travel faster than light, not by breaking the rules, but by bending space itself?
04:25His answer was, maybe.
04:28He imagined a warp bubble, a region of space surrounding the ship that moves with it, carrying it along like a cosmic conveyor belt.
04:37In this bubble, the spaceship itself doesn't move.
04:40The space in front shrinks, the space behind stretches, and the ship rides the wave forward like a surfer gliding on a moving sea.
04:48Inside the bubble, the ship feels no motion.
04:52It's sitting still.
04:54But the bubble carries it across huge distances.
04:58And because the ship isn't moving through space faster than light, it doesn't break Einstein's rules.
05:04The universe itself does the moving.
05:07That hypothetical bubble would need a special kind of energy to bend space-time this way.
05:12Originally, Alcubierre's equations required negative energy or exotic matter.
05:18A substance that's never been found in usable amounts.
05:21Early estimates said we'd need more energy than Jupiter could provide.
05:26For years, scientists have wondered if the universe could allow something like a cosmic shortcut without breaking the known rules of physics.
05:34While nothing practical has been found yet, theorists have explored models that closed time-like curves, loops in space-time that bend back on themselves.
05:44Here's how it works.
05:45Imagine space-time as a giant sheet.
05:48Normally, moving across it takes time, like walking across a field.
05:52But a closed time-like curve is like drawing a circle on that sheet.
05:56If you walk along it, you could eventually end up back where you started.
06:01In space-time terms, the start and end could be different moments in time.
06:06So instead of just moving through space, you're following a path that loops through time, a theoretical shortcut to the past.
06:15This isn't pressing a button to hang out with your younger self.
06:18Einstein's math already lets space-time do gymnastics near spinning black holes, twisting like a cosmic corkscrew.
06:36Physicists can explore these loops on paper, but creating one in a lab is far beyond our reach.
06:43If one day we could turn this math into a real spaceship, a warp bubble wouldn't actually make the ship go faster than light.
06:51Well, technically, there would be no speed.
06:54Inside the bubble, the ship wouldn't move at all.
06:57Instead, it would fold space like a piece of paper, bringing two faraway points together.
07:02The ship could get there in minutes while still obeying the cosmic rules.
07:08This is how it worked in the famous Star Trek series and what many movies adopted as a method for space travel.
07:15In a hypothetical situation, a warp bubble wouldn't just be for spaceships.
07:20You could send a probe, a package, or even a cup of coffee across the galaxy without it actually moving through space.
07:26It's pretty cool, because since the bubbles move space around it, everything inside stays totally still relative to the bubble,
07:35which means no spills and no weird forces acting on the coffee.
07:41However, we are still far away from that point.
07:44The challenges we face are pretty massive.
07:47We still don't have enough energy, and folding space-time at will is still out of our reach.
07:52But for the first time, the math suggests that it's not impossible.
07:58What used to seem like pure sci-fi is now popping up in real science journals.
08:04These concepts aren't just about whipping up time machines or warp drives.
08:08Even if we never pull off a warp drive, figuring out how space-time works is a big deal for understanding reality.
08:16For now, it's all theory and simulations.
08:20But every experiment pushes the impossible line a little further.
08:25Yesterday, it was no.
08:27Today, it's maybe.
08:29And in science, maybe is where the most exciting things happen.
08:33So while we're not ready to build time machines or bubbles across galaxies yet,
08:38scientists can now study and test these ideas using real physics.
08:43Which will lead to new, exciting discoveries.
08:47That is, unless future Earthlings figure out how to do it maybe 1,000 years from now,
08:52so they travel back in time to show us how we can do it ourselves.
08:56Which will create a grandfather paradox.
08:59Unless someone sends the idea back in time and creates a closed time loop.
09:04That's it for today.
09:06So hey, if you pacified your curiosity, then give the video a like and share it with your friends.
09:11Or if you want more, just click on these videos and stay on the bright side.
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