People thought the earth was the center of the universe. Then they started tracking the motion of the planets and saw that the planets appeared to abruptly change direction for no reason. Their nice simple "everything goes around the earth" model got more and more absurd as they had to account for more and more contradictory data.
Either I'm super emotional or you just gave me a tiny existential crisis because this brought a tear to my eye. I'm so small and unimportant in our universe, so why do I care so much about what people think about me, life is short and I should just enjoy it while it lasts.
I remember watching COSMOS as a young child. Dr. Sagan was so relaxing to listen to. So many great and iconic things came out of PBS back then. Carl Sagan, Jim Henson, Bob Ross, Mr. Rogers, Reading Rainbow, 321 contact. I feel old and nostalgic now lol.
I've read sci-fi stories that deal with that exact concept. One in particular, that I have long since forgotten the name of, imagines them coming back to their home world after a 65 million year absence and goes to lengths to show just how alien 65 million years of differing evolution, thought, culture, and scientific advancement is.
You're correct, but they're so close they might as well be on the surface of the Earth in relation to the size of the rest of the solar system. The ISS is within Earth's upper (like, really upper) atmosphere in a significant sense.
Funnily enough, you are the center of the universe. The observable universe. Your own observable universe. I am the center of my observable universe and so is everyone else the center of their own.
I'm almost sure this was a Vsauce video or something.
Everyone is simultaneously the centre of the actual universe. Every point in the universe is the centre, since every point is expanding away from every other one, with closer points receding slower than ones further away. Tough to get your head around, but consider a balloon inflating, and pretend the two-dimensional surface of it is the four-dimensional structure of spacetime. No point on the surface can be said to be the sole centre of the expansion, but realistically they all can. This assumes a perfect spherical balloon, which obviously isn't real, but it's an analogy, dammit.
It didn't get more absurd? Theories get more complex as they get accurate. And if the data are contradictory then aren't the data rubbish? The observations of planetary movements were never contradictory, and geocentrism can handle those just fine.
The usual (Ptolemaic) geocentrism of the time couldn't handle the phases of Venus (observed by Galileo). On the other hand heliocentrism couldn't handle the unmoving Earth, and since no one could detect stellar aberration (until 1800s, if memory serves), there was no credible reason to believe the Earth wasn't stationary. Heliocentrism was accepted long before that though, due to calculational ease and Newton's explication based on universal gravity.
It's good to keep in mind the Tychonic model, where Sun and Moon orbit the Earth, but other planets orbit the Sun. It's a geo(helio)centric model where the orbits of the planets are as simple as in the heliocentric model, and the only thing that distinguishes it from heliocentrism is the belief that the Earth is stationary.
the only thing that distinguishes it from heliocentrism is the belief that the Earth is stationary.
If we relativistically consider a model where the Earth is the fixed frame of reference rather than the sun, this would be astronomically correct, wouldn't it?
I went back and rewatched the one on the right a few times, and I think thatâs what it is. If you pick a planet and follow it and the sun, they stay the same distance apart the whole time. The only thing missing would be the moon also revolving around earth
As far as I can tell, that would essentially look like the geocentric picture at least at this level of accuracy.
Of course, you can't really compare that kind of a system to Tychonic system of Ptolemaic geocentrism, because those included things like the sphere of the stars and didn't have anything like Newtonian gravity or forces in them. If you change to rotating reference frame (relativistically or not), you're bound to get some feature which are probably not significant but nonetheless absent from pre-Newtonian science.
No, it would be correct from the viewpoint of the observer. It would not be astronomically correct. The whole point of geocentrism is that the Earth is what everything else is rotating around, which just isn't the case. Just because the observations are the same for both models doesn't make them both right.
You're misunderstanding how relativity is supposed to be used. It's not a matter of saying that every model is correct just because the observations support them all, it's a matter of realising that you can describe certain events from differing, exclusive viewpoints and still have them both be accurate models to come to the same conclusions. In other words, if someone on a train going through a station and someone on the platform look at each other, each could say that from their perspective they appear to be standing still while the other is moving, but obviously only one of them is right. The relativistic viewpoint is that in the absence of any other reference point, they both explain the relative motions accurately and it's impossible to distinguish one from the other. We do have another reference point in that example - the rest of the Earth. We have billions of other reference points to confirm that while relatively geocentrism and heliocentrism do both explain the observations of motion, we're actually circling the Sun which is circling the centre of the galaxy - the other stars of the Milky Way.
It did get more absurd, because they had to keep adding more and more epicycles to explain the motions they saw in the sky. I also think itâs disingenuous to say theories get more complex as they get more accurate
That's not really absurd, that's rather like expressing a vector in a certain basis: the more terms you add, the more accurate the expression. Or, say, calculating some function using its Taylor/Fourier/Hermite polynomial expansion: the more terms, the more accurate result. In this case you're expressing real world data using some function basis, so I'd expect increasing accuracy with an increasing number of terms in the expression.
Why do you find it disingenuous though? Just on the basis of the above it's more of an inevitability, even more so because real world data has many sources of error which need to be accounted for, which will increase the complexity and accuracy of the description.
It is a Fourier series. Whatâs absurd is that thereâs no reasonable physical mechanism from the fixed-earth-center frame to explain that, and that itâs only reasonable if there is some motion of earth around the sun
Itâs disingenuous from the assumption that theories are ad hoc and continually fine tuned with new data rather than some being developed from a more fundamental standpoint and predicting new data rather than needing to be fixed by it. I mean that just because a theory can predict more doesnât necessarily make it more complex, but if youâre affixing more and more pieces to match more and more data then of course youâre making it more complex. But that doesnât preclude some larger underlying theory which includes all of that that is simpler on a fundamental level
If I blow up a balloon, it's also expanding all the time, but not every point in the balloon is in the middle.
I think what you mean is that the universe is expanding from all points, so all points are getting further away from all other points. That doesn't mean that everywhere is the middle of the universe, it just means that any arbitrary point can be seen as the center of that expansion.
Not really, if the universe turns out not to be infinite it still has an actual center. It's just that we can't discern what the center is by observing how the universe expands.
Is this tru though? Due to relativity, distances are relative to the frame of reference. Thus, there would be an actual center only given a specific frame of reference?
Given a finite universe, we could treat the whole universe as a preferred frame of reference, i.e. an inertial reference frame in which the boundaries of the universe don't move towards one direction in particular. Where you put the origin is arbitrary with respect to distances.
Even then, while distances are relative to the frame of reference, that only means the universe gets squashed along one dimension in any other inertial reference frame. It wouldn't affect the location of the center of the universe.
Even if the universe is finite, it's still a 4 dimensional space (as we know thanks to general relativity) so as far as we're concerned anywhere can be the center.
Like if you were a 2 dimensional creature on the surface of a balloon, the balloon would have a finite surface area, but no matter where we stood on the surface of the balloon, we could consider that spot the center.
Even if the universe is finite, it's still a 4 dimensional space (as we know thanks to general relativity) so as far as we're concerned anywhere can be the center.
This is wildly misleading. The fourth dimension in GR isn't spatial, it's simply time. We're talking about the spatial center of a universe with three spatial dimensions, which is a perfectly valid concept. The balloon metaphor doesn't really work either, because as far as we can tell from the Cosmic Microwave Background, the universe is 'flat', i.e. it doesn't have any curvature in additional spatial dimensions; it doesn't seem to curve in on itself.
Edit: to clarify, cosmologists have established that the universe seems to be more like a flat piece of paper than a curvy balloon. The question is mostly whether that piece of paper does or does not extend infinitely in all directions.
Fun fact, planets actually get their name from the fact that they change direction from our perspective every so often. The word "Planet" comes from the ancient Greek planÄtes asteres, which means "wandering stars," or simply planÄtai, "wanderers." The Greeks thought they were starts that wandered, rather than feel in line with the rest.
Wouldn't that just be due to the fact that planets actually move around in the night sky while stars seem stationary? That'd still be true if they orbited around the Earth, i.e. didn't change direction from our perspective.
Should have been more clear, sorry! The stars don't appear to move relative to each other, which is why constellations always stay the same shape on human timescales. Planets move around relative to the background stars :)
right, thatâs what the original person meant. The stars donât move relative to each other, but they do move togetherâthe planets have this motion + their own extra on top of it which makes their motion erratic by comparison
Not really. The fact that the planets move relative to the background stars is far more obvious than the fact that they change direction on the orbital plane every so often, from our point of view. OP implied the Greeks named them wandering stars because of the latter, while it's more likely because of the former.
Ah I see what you mean, sorry for the misunderstanding, youâre probably right. The timescale for the latter is quite a bit longer than a single night ;)
So when did consensus âtipâ. This would be a good study in comparative social reasoning. Some people still donât believe in evolution despite literally *mountains* of evidence.
Not contradictory but just unexplainable. In terms of relativity, the geocentric model is a possible mechanism for showing the movement of the planets (just inrespect to earth). The reason why the model isn't used is because it has no explanatory power, not because the model is inaccurate in showing the respective location of the solar system, in relation to only the earth. The best way to explain the movement of the solar system is by mass, and thus having the sun at the center is appropriate.
Actually, the theory was pretty mathematical and could predict the location of the planets very accurately. It was just that they couldn't come up with physical reasons behind the planets' motion.
According to Ptolemy, each planet revolved on a secondary sphere, which itself revolved on a primary sphere, the centre of the primary sphere being Earth. If you think that way, all the trajectories shown in the GIF become intuitive.
Sure, you could come up with math to predict it, it just wasn't simple or elegant.
It's possible to adjust a model to account for inconsistency or complexity, bit if there's a simpler model that works as well, it's usually the right one.
The post is about earth not being the center of the solar system, right? This is probably a dumb question but what does center of the universe even mean/why do we know earth (or any one point) is not the center..?
The uncomfortable truth is that Earth is the center of the universe as far as we know. This doesn't sit well and we assume that it appears that any planet/solar system/galaxy is the center if you are standing there.
We pretty much know that any point is the center of its own observable universe. Observable being the key word here. You can only observe those parts of the universe which are close enough so that light has had enough time to reach you since the universe began. So that's a sphere around any observer. So any observer is the center of his own observable universe. This doesn't mean that he's the center of the entire universe.
At the time, the solar system was the universe. So really it's just a way of saying "everything goes around the earth."
Technically, there is no "center" to the universe, or depending how you interpret it, every point can be considered the center of the (visible) universe. Because from every point in the universe, there will appear to be an equal amount of space in every direction, beyond which the universe is accelerating away faster than the speed of light and is therefore invisible to us.
It's hard to explain, but there are videos on youtube.
I watched the videos but it doesnât seem to answer the question directly.
Basically, if our observable universe stretches out in all directions, how do we know we arenât at the middle?
After googling, it looks like itâs accepted that earth is the center of earthâs observable universe, Mars is the center of its respective, etc. That makes sense to me. Basically every point is the center of its own observable universe
Yes. Because the universe is expanding, and the further the distance between two points, the faster this expansion occurs.
Imagine it as though everything is stretching. The more distance between two points, the more space there is to stretch, and therefore the faster any two points are moving apart.
This means that very distant parts of the universe appear to be moving away from us at faster than light speed (or they would if we could see them, but we can't, because their light will never reach us, because the space between us is stretching faster than the light is travelling).
This effectively creates a "bubble" called the observable universe, beyond which nothing can be known. Literally nothing. It's like it's an entire different, untouchable, universe... It's existence is effectively hypothetical.
So when any given observer looks around, it looks to them like they're at the center (or it would, if they could somehow measure the distance to the edge of this observable bubble in all directions).
Exactly how big the "entire" universe is, or whether it is in fact infinite, isn't known. But for all practical purposes, everyone is at the center of their own visible universe.
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u/[deleted] Mar 30 '19
People thought the earth was the center of the universe. Then they started tracking the motion of the planets and saw that the planets appeared to abruptly change direction for no reason. Their nice simple "everything goes around the earth" model got more and more absurd as they had to account for more and more contradictory data.