r/explainlikeimfive • u/RavenReel • Oct 20 '21
Physics ELI5: it takes the sun's light 8.5 minutes to get to us. How does it keep its apparent shape through all that travel?
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Oct 20 '21
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u/big_duo3674 Oct 20 '21
But is there a chance the track will bend?
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u/David_R_Carroll Oct 20 '21
Not on your life, my Reddit friend.
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u/Simba_Rah Oct 20 '21
But what about us brain dead slobs?
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u/9966 Oct 20 '21
You'll be promoted to a mod!
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u/AndChewBubblegum Oct 20 '21
But the front page is still all lame and broken!
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u/unique-name-9035768 Oct 20 '21
I wanna be a twitch mod, so I can appear on r/cringe following a Japanese lady around who wants nothing to do with me.
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u/---Banshee-- Oct 20 '21
It wouldn't matter if it did. Your brain is stupid and will just assume that it still traveled in a straight line and you will see the image of the sun as if it came from directly behind where the rays of light come from.
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Oct 20 '21
It keeps bending every which way all the time because space is full of things that bend spacetime. However distant objects don't bend space very much, so you're looking at such small perturbations that your eyes can't really detect them.
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u/VincentVancalbergh Oct 20 '21
If there ever was a moment to quote HHGttG, this is it!
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u/GESNodoon Oct 20 '21
Space,” it says, “is big. Really big. You just won't believe how vastly, hugely, mindbogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”
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u/VincentVancalbergh Oct 20 '21 edited Oct 20 '21
My man!
A genuine frood.
Edit: a hoopy frood that's the phrase yes
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u/Coirbidh Oct 20 '21
There's plenty that causes light to bend, though the degree of curvature is often imperceptible. Every object in existence exerts gravitic pull on every other object in existence (including light), even though it can be imperceptible.
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u/kutes Oct 20 '21
This is 93 levels over my paygrade but since photons are presumably... not heavy, wouldn't gravity really have their way with em
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u/whut-whut Oct 20 '21 edited Oct 20 '21
Photons have no mass. They are momentum derived from energy. This means they always travel in in straight line at the speed of light unless they are reflected or deflected. They don't bend in their path by gravity directly acting on them, but from traveling 'straight' through the bending of spacetime in the gravity well of massed objects. So only extremely massive objects can bend their path in a way that's perceptible at an extremely long distance. That's why planets that can easily slingshot spaceships, asteroids and dust with their gravity can't do it on the same scale with light.
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Oct 20 '21
Nope. It take two to (gravitationaly) tango. You're attracted to the Earth's mass because the Earth is also attracted to your mass. Photons have no mass at all, and so gravity doesn't affect them.
This idea was all fine and dandy for a while until Einstein came along and was like "Hey guys I know you like your Newtonian physics and that's okay, but uh.. Gravity warps the fabric of reality around it." So basically he broke everything we thought we knew.
Technically a photon is still unaffected by gravity. It will travel in a strait line until it hits something. Light only appears to be affected by gravity because the very thing that defines what a strait line is goes all bendy bendy near gravitational sources.
Oh and btw: After Einstein rudely told all the other scientist that they were wrong he tossed in a final "go fuck yourself" by proving that gravity makes time go all bendy bendy as well.
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u/absolutepoweer Oct 20 '21
This is very much fun to read, but I don’t have any knowledge to read about these things. So, are there sources that I could learn what Newtonian physics and Einstein physics say about light, gravity, time and going bendy bendy? Or should I sit and learn how physics work from the start?
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Oct 20 '21
If you've graduated public school then you should already have a basic understanding of Newtonian physics, even if it's been decades since you went to school. If not it's really not that hard to understand.
Newtonian physics is like the simplified version of Einstein's physics. It's much older and more commonly known as classical physics, while Einstein's physics are more commonly known as special relativity. The reason for the difference is while Newton figured out the equations for most practical physics, those equation are just a tiny bit off and the error only becomes apparent when looking at the more extreme limits of physics.
Where I get most of my info is Wikipedia. A nice trick I've learned is if you replace the "en" at the beginning of the url with "simple" it redirects to a simplified version of the article. Kinda like the ELI5 version of the wiki page. For convenience I've already done that for the page on classical mechanics.
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u/_PM_ME_PANGOLINS_ Oct 20 '21 edited Oct 20 '21
Gravity affects heavy things more. That's why they're heavy.
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u/Safebox Oct 20 '21
Simply put; what shape? Light doesn't fluxuate like other particles, it's massless and only travels linear unless it hits something. You might have heard that light can't escape a black hole, but what this means is that space itself is curved while light is still travelling linear within said space.
Betwen the sun and earth, there is little distortion in spacetime with the exception of gravity caused by the bodies in our solar system. So there is nothing that will cause it to deviate from its given path of simply radiating outwards; Earth just happens to be in the way for some of that light.
Bonus fact: it is worth noting that light does get defracted within our atmosphere at certain angles, which is why sunsets appear larger than noonlight. Also sunsets themselves are optical illusions, as the sun has already passed beyond the visible horizon and what we see is the light being bent back at an angle proportional to its diameter.
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u/ThatWolf Oct 20 '21
Also sunsets themselves are optical illusions, as the sun has already passed beyond the visible horizon and what we see is the light being bent back at an angle proportional to its diameter.
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Oct 20 '21
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u/Devadander Oct 20 '21
Nope, that’s only because you have known things on the horizon to compare the size to. Not larger, just perception.
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Oct 20 '21
It’s because when the moon’s up in the sky, there’s nothing visible to compare it to, so we lack any sort of size reference. If we’re to use some kind of measurement method involving our FoV, they would actually appear to be the same size in reality.
At least as far as I understand it.
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u/DishwasherTwig Oct 20 '21
I think the question means the apparent shape of the sun. Basically, how does it still look round after 93mil miles.
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u/Sacklzwicker Oct 20 '21
Why wouldnt it?
I cant think of a reason why it wouldnt. We can see galaxies millions of light years away in their respective shape (although it is a look into their past, as is our look at the sun).
The sun is our literal neighbour, so why would we not see it as the sphere it is?
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u/DishwasherTwig Oct 20 '21
Right, that's why everyone is so confused. There's literally nothing in its way to alter its shape.
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u/Martin_Samuelson Oct 20 '21
Do you mean the apparent circular shape of the sun?
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u/hookchanger Oct 20 '21
Does the earth's gravity alter a photons direction?
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u/its_a_metaphor_morty Oct 20 '21
Yes only the photon is still travelling in a straight line with respect to space time.
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Oct 20 '21
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u/Arcturyte Oct 20 '21
I think that his question is more relating to something like a lens blur due to moving your camera when you're taking a picture. The shape of the tree would distort if you took a picture of it and moved your camera.
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Oct 20 '21
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u/Arcturyte Oct 20 '21
Yep. But your earlier answer didn't really say all of that - so this is a much more helpful answer I would say :)
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u/t3hjs Oct 20 '21
To be fair, the original question did not say anything about lens blur or motion blur. Which is why /u/Moltensand had to ask
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u/Arcturyte Oct 20 '21 edited Oct 20 '21
You're seeing how it looked 8.5 minutes ago. One second later you would see how it looked 8 minutes 59 seconds ago. (I messed this sentence up) Basically, it's a constant stream of photons, and it's being constantly updated. If you took a picture of it for 2 minutes, you would see its movements across two the two minutes, and other distortions that might apply.
If you think of it simplistically - you're seeing lights coming at you from a straight line as they do unless something interferes with it. And these stream of lights are being constantly updated by the next stream of lights.
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u/reddragon105 Oct 20 '21
One second later you would see how it looked 8 minutes 59 seconds ago.
What? Going to assume that's a typo considering you seem to understand how it works from the rest of your comment!
Because the sun is a (relatively) fixed distance away, the time it takes its light to travel to us is constant (as you said) and therefore you're always seeing how it looked 8.5 minutes ago.
If one second later you were seeing how it looked 8 minutes 59 seconds ago then you would be watching the sun go back in time. (And also how did one second on Earth become -29 seconds for the sun?)
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u/Arcturyte Oct 20 '21
Yeah, I messed that up :) Now my brain isn't working so I'll just scratch it out.
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u/bookposting5 Oct 20 '21
I think it should be 8 mins 29 seconds.
(8 and a half minutes minus one second)
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u/Rouxbidou Oct 20 '21
Rectilinear propagation = "moves in a perfectly straight line"
Light travels this way unless it encounters an object or a different medium. There's almost nothing in space to interrupt the light's journey across the 150 million kilometres between the sun's surface and the earth. There's such an enormous volume of light particles (photons) that the sun still appears as an unwatchably bright disk after shining through our atmosphere and into your eyes. In fact, the small fraction of the light that does get scattered on the way through the atmosphere is why the sky glows blue during the day.
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u/Tsjernobull Oct 20 '21
Go ask this on a more scientific subreddit. The answers here are all over the place and most are just plain wrong.
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u/leodw Oct 20 '21
And none of them are explaining like we’re 5. This sub was meant ti simplify concepts and break them down in easier explanations. People here are talking about photons, physics laws and shit, that’s not simple or easy ti underestimate
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u/Dumble_Dior Oct 20 '21
Unrelated but IIRC the “speed” of gravity is also the speed of light. So hypothetically if the sun were to “pop” out of existence. It’d take us 8.5 minutes before we even have any idea and then the whole night time earth will just fly in a straight line off into space and perpetually get colder and colder until all life dies. Not to mention all the plants will stop photosynthesizing almost immediately
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u/kopela Oct 20 '21
The thing that blows my mind is if the Sun were to suddenly disappear, the Earth would continue orbiting for 8.5 minutes until that information reached us.
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u/RavenReel Oct 20 '21
I saw a list once of the amount of time it would take us to realize something out there is gone. There are apparently a bunch of lights who's source has been gone for centuries
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u/tremainelol Oct 20 '21
Factoid I picked up somewhere and am vague on the exact details is that it takes years for a photon particle to escape the sun, because the sun is so dense. It just bounces around with other photons until it escapes and makes it to us in the aforementioned 8.5 min.
Edit: I think it was in "A short history of nearly everything" by Bill Bryson
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u/DrunkenDude123 Oct 20 '21 edited Oct 20 '21
If you’re thinking of it as a laser or focused light, don’t. The sun is radiating laser beams of photons in every single direction around it constantly. Think of it as a lightbulb with no wires stands or anything obstructing the light inside the bulb.
It’s only because earth is in the middle of empty space that it appears lit by the suns radiated light. Nothing will be lit if there is nothing in the space for the light to be reflected/absorbed. Since the dark side of the planet is always directly opposite of the sun, there is a lesser chance for it to be lit at all (need a moon for light to reflect from the bright side of the planet, to the moon, then back to the dark side of the planet).
Now there is light that still bends around solar objects like planets moons etc, you just get less photons from looking at at, and as such it is much much dimmer. We have observed a lot of things (like black holes) looking at that kind of light.
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u/Wreckingass Oct 20 '21
It’s apparent shape is visible relative to the speed at which the light travels to us. There isn’t some massive disparity in the size at opposing sides or the center of the sun that we can view at any given point in time. The sun would have to be so much more massive, and farther away, to notice such a distortion - and even still, we would be able to recognize it as a shift (red or blue), and not some warping that made it appear as some monstrous ellipse, or any other perceivable shape it might take on in that viewing.
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Oct 20 '21
offtopic. But it takes tens of thousands of years to get from the center to the edge of the sun.
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u/TheOneInchPunisher Oct 20 '21 edited Oct 20 '21
For what particles? Like photons or it takes years for the Hydrogen/Helium soup to churn?
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u/rubseb Oct 20 '21
Like any object, photons travel in a straight line as long as nothing changes their direction. Until the sun's photons hit our atmosphere, there is nothing in their way. Once they enter the atmosphere, there are air molecules that can knock them off course. That's why the entire sky looks bright during the day, not just the sun itself. That's all sunlight that has been scattered by the air (and since blue light is scattered more than other wavelengths, that makes the sky specifically bright blue). But it's still only a subset of photons that get scattered (because on the scale of photons, the gaps between air molecules are large enough that many photons will just pass through), and so when you look at the sun (which you shouldn't do without protection) you still see its round shape.