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PathRepresentative77 t1_iybcclo wrote

In two sentences: Acceleration allows you to trade how quickly you cover a distance with how quickly you cover a time interval. The higher the speed you accelerate yourself to, the more distance passes, but the less time passes.

This is somewhat common sense--the faster you drive your car, the less time it takes to get somewhere. Where it gets funky is that the universe has set it so that, for something going the speed of light, time never passes. Human common sense would dictate that, if you go an infinite speed, time never passes. The universe somehow set this maximum speed at "speed of light" instead of "infinite speed"--and makes it so that everything that sees light sees it traveling at the speed of light.

This is counter-intuitive. If one car is traveling at 20 mph and one travels at 30 mph, the first car sees the second traveling 10 mph relative to itself. If there's a sudden flash of light in the distance, both cars see the light going at the same speed. To make this work, the universe has to change how the two cars individually measure space and time.

This is where acceleration comes in. If two people are moving at different constant speeds, they'll experience space and time differently--but there's no way to tell who is right. As far as science and philosophy goes, they're both right. As soon as one of them accelerates, they're using energy to change how they experience space and time while still measuring the speed of light as constant the entire time.

That constant-speed-of-light thing is what messes up everything. If you're accelerating a car down the road, a speed gun in the car should measure all the stuff passing by as going faster and faster--NOT constant. The universe goes wonky to keep light speed constant.

If you flew away from Earth in a spaceship and looked at Earth while doing so, common-sense says that everything would appear to be going in slow-motion--since you're getting further and further away, light has to travel a longer and longer distance to reach you. Now keeping in mind that your rocket had to accelerate to get you out of Earth's gravity well, the universe's wonkiness steps in so that they also appear to be going in slow motion because you've changed how you are now experiencing space and time.

Edit: to answer the Interstellar question. Acceleration is caused by an imbalance of forces--things pushing and pulling on you. This includes experiencing gravity. If you're in a gravity well, congratulations--you're accelerating compared to the rest of the universe, and are actually aging slower than the rest of the universe. With Earth's gravity, it's not a huge effect. If you're around a black hole, it can be huge. The closer you get to a black hole, the more you feel the force of gravity, the more you're accelerating, the slower time passes for you. In the movie, they got closer to the black hole when they got to the planet. The guy on the ship was further from the black hole, so time passed faster for him. The actual numbers of 7 hours vs 23 years just comes from math.

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Belligerent_Christ OP t1_iybdryf wrote

Holy shit

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PathRepresentative77 t1_iybetus wrote

Does that make any sense?

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Belligerent_Christ OP t1_iybfgqr wrote

For the most part. But your edit created another question. How the hell does gravity effect time?? So if there's zero gravity or negative Gs does that mean your aging faster? Lol wtf

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PathRepresentative77 t1_iybg2bw wrote

Exactly. If there's zero gravity, you age faster than if you feel gravity. Negative Gs, I'm not sure, just because I don't know what that is. From a physics standpoint, you can't have less than zero gravity.

The universe is weird, dude. Weird and wonderful.

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Belligerent_Christ OP t1_iybgtti wrote

What's the conversion rate? 1g vs 0g? I'm probably thinking of it from a flying perspective. If I pull down on the stick blood goes to my legs +Gs if I push up blood goes to my brain -gs

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PathRepresentative77 t1_iybi8dq wrote

Yeah, the negative Gs with flying is different. Different parts of you are being accelerated differently to other parts and to planet Earth, so the biological sensation is negative Gs, but the physics measurement is all still acceleration, period.

Also, I don't know how I keep missing questions. To answer your gravity question... Basically, space and time are connected. You can't experience them separately. If you change how you experience one, you change how you experience the other--they call it "spacetime". This is essentially where matter and energy exist, and where they do all their stuff--it's the "fabric of the universe" everyone is always talking about. Gravity "warps* spacetime.

We're getting a little in the weeds, but we know this warping happens by looking at how light travels. We assume light travels in straight lines on space-time without gravity. Unlike regular matter, you can't really push or pull light with a force--it can't accelerate because it is constant. The only way to make light turn is by curving what it is traveling the space-time it is traveling on. Massive things with a lot of gravity deflect light, so the conclusion is that gravity is curving space-time. The result for normal matter following this curved space-time is time dilation.

In terms of actually measuring this, it looks like things get bent in pictures and in telescopes. If you ever see the "gravitational lensing" photos from Hubble or James Webb telescope, that's what we think we're seeing--light being deflected by gravity. It's called "lensing" because someone figured out that gravity bends light like lenses--so we can use them like lenses in a giant telescope.

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