524
wat (lemmy.dbzer0.com)
submitted 5 months ago by to c/memes@sopuli.xyz
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[–] 229 points 5 months ago (38 children)

Take a balloon.

Blow it upto about 50mm

Make a couple dots around it

Blow it up a little more.

Now there's distance between the dots.

Imagine an ant walking between the dots. That ant is going at the speed of light (as fast as it can go) relative to the dots.

Now as it walks between the dots, blow the balloon up really big

The dots aren't moving, they're stuck to the surface of the balloon. The balloon itself is expanding. The ant is going at the speed of ant-light, but now the dots are all "moving away" faster than the ant can walk.

The speed of the ant hasn't changed, the space the ant is traveling has changed. And faster than the ant can move, because the balloon isn't limited by the same things the ant is.

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  • [–] 60 points 5 months ago (1 child)

    Thanks for that that's actually a really helpful analogy.

    I mean i still dont understand. Brain hurty. But thanks anyway

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  • [–] 5 points 5 months ago

    Things cannot move through space at a speed faster than lightspeed.

    This rule does not apply to space itself.

    Also, interestingly, shadow boundaries can 'move' faster than the speed of light.

    https://www.iflscience.com/shadows-can-move-across-a-surface-faster-than-the-speed-of-light-75112

    Because a shadow isn't truly a 'thing'.

    Its just an area where light bouncing off of something is not happening (as much).

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  • [–] 17 points 5 months ago (2 children)

    This is a truly great explanation. One worthy of Feynman. Physics degree?

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  • [–] 16 points 5 months ago (1 child)

    Lmao no, just autistic fascination with space and many thousands of hours of listening to astrophysics lectures and hundreds of hours listening to edu-tainment type videos from people like Dr. Becky Smethurst.

    Thanks for the compliment though, I've heard the balloon explanation since I was a child, but the ant-splanation of light speed just popped into my head.

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  • [–] 34 points 5 months ago (7 children)

    All we are going to die?

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  • [–] 11 points 5 months ago (3 children)

    Eventually, the universe itself will "die" when it hits absolute zero and nothing moves anymore. Nothing can happen after the heat death of the universe (unless protons decay)

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  • [–] 2 points 5 months ago

    Not unless you donate some seed money to my church. It will come back to you, and then you pay twice as much and then I pay half. And then you, a vulnerable population, gain faith in the process and give more and more and I give less and less but this is just friendly educational propaganda from your friendly neighborhood juggler and CIA spook.

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  • [–] 10 points 5 months ago (19 children)

    The space between atoms starts to expand faster than the speed of light. Well i guess that is the universe fucked.

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  • [–] 13 points 5 months ago (16 children)

    Good thing the atoms (and the subatomic particles) are pulled back together as the universe expands. The same way we are pulled to Earth by gravity and don't fly off into space as the universe expands.

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  • [–] 12 points 5 months ago* (15 children)

    This does, however, lead to the existence of "local groups".

    Meaning that, there is a local group of celestial bodies that we may theoretically be able to visit at some time in the future, which are held somewhat together by gravitational forces which help to counteract the expansion of space. But anything outside of that local group will be expanding away from the group at greater than the speed of light.

    Meaning, effectively, that the universe is going to be / is already separated out into small pockets of local neighbors, who will never be able to reach other local groups unless they invent some sort of much faster than light travel. The universe is very, very large, but the percentage of the universe that is physically reachable by us is quite small, no matter how many generations we spend on the journey.

    Personally I find that to be one of the more disappointing true facts about the universe.

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  • [–] 7 points 5 months ago (14 children)

    Exactly, there will be causally disconnected pocket universes in the future. I'm thankful we still live in a time when we can see the rest of the universe. Creatures alive in 100 billion years might have no way to figure out how the universe started, or that there is anything outside of their local cluster at all.

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  • [–] 3 points 5 months ago (13 children)

    I'm thankful we still live in a time when we can see the rest of the universe.

    Do we though? How do you know our entire known universe isn't just a local cluster?

    If we could see the entire universe, then somewhere in the center we'd be able to point to the origin of the Big Bang. Since we can't, that implies we're only looking at a section of the universe analogous to a portion of the surface of a globe.

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  • [–] 2 points 5 months ago (5 children)

    By the nature of the Big Bang and the expansion of the universe, everywhere is at the origin. That is, if we believe that the universe started out as a singularity, and that the expansion of space itself is what causes that singularity to grow, then every point in the universe originated from the exact same point, and that nothing has "moved", in the sense that the point itself is expanding. Thus, every place is at the "origin".

    To use the balloon analogy: Draw a small dot on the balloon, that dot is the entire universe as a singularity. Now, inflate the balloon so the dot grows, and try to determine the "origin" of the dot. Of course, you could point to the centre of the dot, but I would argue that if the initial dot is infinitely small (a singularity) then every point on the expanded dot in fact originates from the exact same point.

    This does cause a bit of a headache because we're arguing that a zero-dimensional thing suddenly became 3-dimensional. I'm honestly not sure how astrophysicists reconcile that, but I seem to remember reading that they boil down to saying "we know what happened after the Big Bang, but we don't really know anything about what happened at t=0" per my understanding, even the concept of time breaks down when you go to t=0, so it becomes impossible to get to t = 0 + h.

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  • [–] 1 point 5 months ago (4 children)

    That doesn't make any sense, down to the geometric level.

    By the nature of expansion itself, there is an origin point somewhere in the center. That holds especially true in the case of uniform expansion.

    If "every point in the universe originated from the exact same point" then that origin point is somewhere in the center of the universe, and tracing the trajectories of every point backwards should intersect somewhere very close to that point.

    Your balloon analogy supports this thesis. No matter how much the dot expands, the center of the dot is where it originated. Yes, every point on the expanded dot originates from the same point. That point is in the center.

    Saying "sometimes physics is mindboggling" in order to rationalize invalid leaps is not a strong argument. Yes, sometimes physics is mindboggling. But that's no reason to handwave away inconvenient facts whenever we're trying to argue for something illogical. You need rigorous evidential support to justify a mindboggling conclusion, as is the case with quantum mechanics. Speculative or theoretical physics however cannot simply fill in the gaps with this sort of handwaving.

    Honestly, if the concept of time breaks down when you look at t=0, then that only tells me that the idea of t=0 itself is invalid and needs to be abandoned. Especially since there's no evidential support for that theory, it's entirely speculative, and has only been justified with the explanation that "We don't have any better ideas."

    Time didn't just magically start at some random point before which time didn't exist. And space didn't just magically expand into 3 dimensions before which there was only 0. Energy and matter didn't just suddenly appear without any prior cause initiating some action. All of those things would require violations of the laws of thermodynamics. And in the absence of far more evidence than ever has or even can be found, this "best guess" is full of more holes than many people seem ready to admit...

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  • [–] 1 point 5 months ago (2 children)

    If “every point in the universe originated from the exact same point” then that origin point is somewhere in the center of the universe

    This is where I'm disagreeing. Since space itself is expanding, every point "originated" where it currently sits, and has "expanded in place" so to speak. You can't really imagine this as an expanding bubble (the balloon analogy was bad here), since a bubble necessarily expands into existing space. In our case, the bubble itself is the space.

    tracing the trajectories of every point backwards should intersect somewhere very close to that point.

    That's where you get a problem. Space is expanding, so if you pick an arbitrary point in space, you'll observe that the universe appears to be expanding out from that point. No matter where you are, and what direction you look, you will see that everything is moving away from you. Thus, if you reverse that process to "trace it backwards", then no matter where you stand, you'll see everything contracting towards you, and conclude that you are at the centre. For reference, Hubble agrees with this interpretation.

    Saying “sometimes physics is mindboggling” in order to rationalize invalid leaps is not a strong argument.

    I'm not trying to make any bombastic claims and hand-wave them away with "physics is hard". I'm trying to give an accurate recollection of the current consensus based on my own understanding of it (which is rudimentary at best).

    Honestly, if the concept of time breaks down when you look at t=0, then that only tells me that the idea of t=0 itself is invalid and needs to be abandoned.

    It breaks down within our current models. You can of course always ask the question of "what happened before X", and the answer today is that our current models can take us more or less arbitrarily close to a singularity (t=0), but not all the way there. There are several theories out there regarding what the "initial state" was.

    Time didn’t just magically start at some random point before which time didn’t exist. And space didn’t just magically expand into 3 dimensions before which there was only 0. (...)

    I'm not really saying it did. I'm saying that, as far as I know, we have no better model or understanding than that if we extrapolate to t=0, we get a singularity (0 D), that for some unknown reason "magically" started expanding into the 4 D space-time we inhabit today. The fact that this process violates pretty much every known law of nature really just means there's something here we don't understand yet. I believe it's pretty well established that our current models more or less completely break down at around the Planck time (see the "in cosmology" section).

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  • [–] 1 point 5 months ago (1 child)

    we have no better model or understanding

    that for some unknown reason

    our current models more or less completely break down at around the Planck time

    Right, so in other words we have some major epistemic gaps that not even the some of every expert in the field can explain.

    That's why it shouldn't be viewed as ignorant to ask questions that put a different spin on the problem, that potentially no one has asked yet. And why "this is the best explanation that we have at this time" is no reason to shut down conversation/speculation about it.

    Returning to my original point:

    Do we though? How do you know our entire known universe isn't just a local cluster?

    How does anybody presume that the universe isn't vastly bigger than what we've observed of it to date?

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  • [–] 1 point 5 months ago

    That’s why it shouldn’t be viewed as ignorant to ask questions that put a different spin on the problem, that potentially no one has asked yet. And why “this is the best explanation that we have at this time” is no reason to shut down conversation/speculation about it.

    I don't view you as ignorant, and it hasn't been my intention to shut down the conversation. If that was your impression, I apologise. I was very honestly just trying to give my own best interpretation of what the common consensus is, and why it is the way it is. Asking questions is an unequivocally good thing, and I enjoy trying to answer them to the best of my (meagre) ability: It helps me gain new perspective.

    How does anybody presume that the universe isn’t vastly bigger than what we’ve observed of it to date?

    I'm honestly not quite sure, but I think it's broadly accepted that the entire universe is far larger than the observable universe. From a more philosophical stance one could ask if anything outside the observable universe should really be considered part of "our universe" since, as far as we know, it is unreachable even for light (hence, unobservable).

    As for estimating the size of the (entire) universe, I think they do that indirectly by estimating the age based on observing the cosmic microwave background, and then estimating the size based on the age and rate of inflation.

    Of course, as with anything in natural science, everything is based on imperfect models that (I personally believe) will never more than asymptotically approach the true underlying reality. Thus, there's always a possibility that anything we haven't explicitly verified empirically will turn out to be completely wrong.

    Someone once asked me how I would react if the second law of thermodynamics was proven to be wrong (I'm a theoretical chemist), and I responded that I see the second law as an extremely good model that's been shown capable of representing a truckload (put mildly) of things accurately. A single counter-example doesn't mean it suddenly becomes inapplicable to all the things we use it for today. The same things apply to Newton's laws, and a bunch of other models that already have been proven wrong. The point is: I see no reason at all to believe our current astronomical models are the "actual truth", but I do think they're good models for the things that we've actually verified that they work for.

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  • [–] 1 point 5 months ago

    I think the balloon analogy does not work well here. As far as we know the big bang was the start of our universes spacetime. There are plenty of theories on what might have happened "before.".

    Here is a good playlist to get you started on learning some more info.

    https://youtube.com/playlist?list=PLsPUh22kYmNAV2T4af0Di7bcsb095z164

    And this video from that playlist is directly related to this discussion.

    https://youtu.be/K8gV05nS7mc

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  • [–] 2 points 5 months ago (6 children)

    Someone else already replied probably better than I can, but this is one of my favorite subjects to study.

    The big bang didn't really start in a place, it happened at a point in time. As we look at all of the galaxies around us (minus the close ones we are gravitationally interacting with) they are all moving away from us, so either 1) we are exactly where the big bang took place (vanishingly unlikely) or 2) the big bang happened everywhere and all of space is expanding from that event.

    We can actually see the first light ever released in the universe (not from the big bang, as the universe was a dense plasma for the first ~400,000 years until the recombination era) as the cosmic microwave background radiation. And it is (relatively) even in all directions, minus some minor temperature variations.

    I highly suggest looking at a channel on YouTube called PBS Spacetime. They have videos going back years and years that dive into great depth on all of these topics!

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  • [–] 1 point 5 months ago (5 children)

    Yes, I already responded to the other comment. Summarily, I don't find their argument convincing.

    To add, it's not surprising that everything is moving away from us. To use the other commenter's balloon analogy, as the balloon expands, so do the circumference and surface area. So any two points on that surface will be moving away from each other as it does so.

    It's also not surprising that the cosmic microwave background radiation appears relatively uniform. 14 billion years of expansion, and we can only observe or "neighborhood" of the universe, mind-bogglingly large as even that is. 14 billion years of moving on a more or less stable trajectory. We can't see far enough backwards to view the origin point.

    Also, if the background radiation came from the big bang, then it would have outpaced us as our galaxy slowed down and the radiation continued moving at the speed of light. This suggests that the background radiation we witness was emitted after the energy that coalesced into our galaxy, and is just now catching up/surpassing us. Unless it's reflecting off of something further outward, and on it's way back.

    Is there any known pattern to the actual direction of cosmic background radiation? Is it aligned in any way or more or less random?

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  • [–] 1 point 5 months ago

    The CMBR was the first light that could ever actually go a long distance in the universe, as before that the universe was opaque plasma. When the universe cooled to a threshold it the. Became transparent to light. This light was released in all directions at all points, which is why we still see it today. It will be detectable until the universe's expansion speeds up to a point where it outpaces the speed of light.

    There are some patterns in the CMBR but only due to density fluctuations. A fascinating topic to look into is the Baryon Acoustic Oscillations. Small quantum density variations that were expanded rapidly as the big bang started going into overdrive that have shaped the universe on an immense scale.

    I don't have time to answer every question you have sadly, and I'm just someone who really enjoys learning about this stuff in their free time. The channel I mentioned has videos on all of this. I highly suggest you start watching those if you actually want an in depth understanding of this.

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  • [–] 1 point 5 months ago (3 children)

    The way you're talking about the CMB and the questions you're asking about it suggest that you're unfamiliar with the topic's particulars. I'd start here: https://en.wikipedia.org/wiki/Cosmic_microwave_background

    You're making intuitive assumptions based in what you currently believe you know. Some of the concepts you're using to framework your thinking simply don't apply.

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  • [–] 1 point 5 months ago (2 children)

    That link doesn't address directional parallelism.

    And if you take my willingness to express a gap in my knowledge as evidence that I just don't know what I'm talking about and that everything I say should be discarded, then I don't know what to tell you. Do you have perfect knowledge, free of any gaps? Or are you simply unwilling to admit to having gaps?

    If I was willing to admit to one gap in my knowledge, then why do you think that means everything else I say must be bullshit? Seems kinda strange...

    Anyway, my main point is that even the experts have major knowledge gaps when it comes to theoretical astrophysics. And they are very aware of that, and willing to acknowledge the incompleteness of their knowledge.

    I was simply pointing out some of the errors in the "best answers we have," explaining why they need to be rethought. If you won't even consider my actual point simply because I freely admit to not knowing whether cosmic background radiation aligns or has a random trajectory, then this conversation might as well be over.

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  • [–] 1 point 5 months ago (1 child)

    Because parallelism is not relevant.

    I did not suggest you ought to discard anything.

    I have considered your point. I then addressed the framework you seem to be using to build that conclusion. You've assumed axioms from what you see as related disciplines are still useful in a context you're admittedly ignorant of. I suggest that familiarizing yourself with domains on which you are ignorant will provide the answers you're looking for.

    It'll also explain why others already familiar with the topic find your reasoning falls short or isn't interesting enough to meaningfully engage with.

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  • [–] 1 point 5 months ago

    Parallelism is relevant. If the background radiation happens to be aligned in parallel fashion rather than at random trajectories, then that indicates something different than if they're moving at random. If it wasn't relevant, I wouldn't have asked it.

    And just because I ask one question about something specific, which is apparently niche enough that the wikipedia page didn't even address it, doesn't mean I'm ignorant on the whole topic. You're too afraid to ask questions you don't know the answer to, because you're afraid it might make you seem ignorant. So you don't think outside the box, you just rehash the pop science that's been packaged for you nice and neatly. That's why you don't find my reasoning interesting enough to meaningfully engage with.

    I'm familiar with the pop science, and that's why I ask questions that go beyond the scope of what typically gets packaged and presented for us laypeople. If that makes me more ignorant than people who read the pop science and then don't ask questions, then whatever...

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  • [–] 6 points 5 months ago

    How fast space expands is described by general relativity. For the space between atoms to expand faster than the speed of light, you need a shitload of energy crammed together very densely, like a galaxy worth of stuff in every atom. This is called cosmic inflation, and it's what happened during (and possibly before) the first part of the big bang.

    We don't know exactly how there can be this much energy in this little space, or where it all went, but we do know it was there because there are waves imprinted on the density of the universe.

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  • [–] 2 points 5 months ago*

    Without trying to explain things even in not sure I grasp, no. The atomic forces keep atoms together, and expansion of space is only noticeable on long distances. Like light-years and parsecs kind of distances.

    Also fun fact: the rate of expansion is not only INCREASING as space expands, last information I saw suggested space is expanding faster in some directions than others, which is fascinating for a number of reasons.

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    • [–] 64 points 5 months ago (2 children)

    Well, nothing (with nonnegative mass) can move faster than light through space. Space itself can do whatever it wants to.

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    • [–] 45 points 5 months ago*

    The universe is mostly nothing. So obviously the universe, being nothing, expanding faster than the speed of light isn't surprising, as nothing is faster than light. 😌

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    [–] 27 points 5 months ago (7 children)

    Preemptive explanatory note: the speed of light, approximately 300,000 km per second, is the highest speed that something can move through space.

    The expansion of space doesn't happen at a set speed. It happens at a rate of approximately 70 km per second per megaparsec. So if you're measuring two points half a megaparsec away from each other, then every second, the space between them grows by about 35 km. If you're measuring two points 2 megaparsecs away from each other, then every second, the space between them grows by about 140 km.

    If you're measuring two points 4300 megaparsecs away from each other, then the spacetime between them grows by about 300,000 km every second. That's not to say that anything is moving at 300,000 km per second, there's just more space between them every second

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  • [–] 18 points 5 months ago*

    Wtf is a megaparsec? It's a million parsecs. Tf is a parsec? A parallax arcsecond.

    ...Tf is a parallax arcsecond?

    An attempt at an explanation for the layperson

    Imagine you're standing outside. In front of you is a tree and behind that on the horizon is a mountain. You move 10 ft to your left, and the tree looks like it moved to the right, but the mountain looks like it hasn't moved at all. That's parallax. The closer something is, the more it appears to move when you move.

    Imagine you are the pivot point on a big protractor. Your field of view can be divided into 360°. Every degree can be divided into 60 parts, called arcminutes. Every arcminute can be further divided into 60 arcseconds. Each arcsecond is 1/3600 of a degree.

    How do these fit together? There's one more thing I need to explain.

    The earth orbits the sun at around 149.6 million kilometers. That's called an Astronomical Unit. A parsec is the distance that an object would have to be, so that moving one Astronomical Unit would make it appear to shift sideways by 1 arcsecond.

    Fraser Cain did a better job explaining, because he can use pictures

    It's 3.26 lightyears.

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  • [–] 2 points 5 months ago (1 child)

    Moving is just putting more space between you and something. If it walks like a horse, talks like a horse, bites like a horse... you get the idea. It's not clear to me why the increase of inbetween space in cosmic inflation "gets a pass" whereas the increase of inbetween of space from movement doesn't

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  • [–] 1 point 5 months ago*

    Apologies for the wall of text. I spent an hour and a half trying to find the most concise way to explain this, and there kind of isn't one...

    There are two ways for the distance between two objects to increase

    There are two ways for the distance between two objects to increase over time. One of them involves displacement through a medium (movement), and the other involves that medium itself expanding. From our perspective, a galaxy 5000 megaparsecs away is "moving" away from us by about 350,000 km every second, but that's only because for every megaparsec between us, the space itself is expanding by about 70 km every second. If you ask a guy smack in between us, he'll say we're both moving away from him at 175,000 km every second. That galaxy isn't experiencing any acceleration in that direction; it isn't moving through space at that speed.

    An attempt at an analogy

    A submarine increases its depth by sinking lower in the water, right? Imagine a tub of water 1 foot deep. Put a toy submarine 6 inches from the bottom, and it's 6 inches underwater. Now add another six inches of water to the tub. Your sub hasn't moved through the water at all, but now it's 1 foot deep. The submarine can increase its depth without sinking at all.

    In fact, if you let the submarine rise slower than you add water, then it can rise upward through the water as it continues to get deeper below the surface.

    The speed of light is a constant

    The speed of light (in a vacuum) is a constant. That is to say, every observer in every reference frame measures every photon (in a vacuum) as moving at 299,792,458 meters per second. This fact supersedes all others. It supersedes time itself. Imagine I'm on a train going 50 mph, and I throw a ball forward at 50 mph. In my reference frame, that ball is going 50 mph. To an outside observer, that ball is going 100 mph. How fast the ball is going depends on your frame of reference.

    This is not true of light. If I'm traveling on a train going half the speed of light and I shine a flashlight forward, the train's speed doesn't add to the light's speed. You and I will both agree that those photons are moving 299,792,458 meters every second, in both our reference frames. This happens because we aren't experiencing the passage of time at the same rate.

    The photons coming out of that galaxy 5000 megaparsecs away are also going 299,792,458 meters per second in our reference frame, even as the space between us grows by more than that in that amount of time. That galaxy isn't moving faster than light, space is just expanding.

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    • [–] 34 points 5 months ago* (19 children)

    Wrong, the expansion doesn't have a speed because it isn't motion. But you have to think about it longer than you'll probably want to before hitting the up or down arrow and/or scrolling.

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  • [–] 16 points 5 months ago (7 children)

    Best analogy I heard for it is if you put a load of dots on a balloon, then inflate it. Are the dots getting further away? Yes. Is there just the same amount of rubber between each dot as when you put the dots on? Yes. Can you measure the relative speed of the dots? Yes! But have they actually gone anywhere? No...ish?

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  • [–] 4 points 5 months ago (3 children)

    Yeah, but in this case is the universe just the dots on the surface of the balloon or is it the whole balloon with its entire volume? Intuitively I think it's the latter (although there's probably no "hard" edge that's bounding the ends of the universe like the rubber of the balloon), and if that's true, you could measure the speed of one wall getting away from the centre or the speed of two opposite walls getting away from each other.

    I could be wrong of course, I'd be happy if someone points out what I might be missing.

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  • [–] 1 point 5 months ago

    Yep I think you have to imagine dots suspended in space inside the balloon to better get what's going on, and you're right, the "edge" of the universe is definitely nothing like the surface if the balloon. Probably?

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  • [–] 26 points 5 months ago (9 children)

    Best intuition I've heard for this is that "things" can't move faster than light, but not everything is a "thing".

    Imagine doing shadow puppets on the wall with a flashlight. You move the bunny left, shadow moves left. The further away the wall is, the faster the apparent speed of the shadow bunny. You might think that, far enough away and with a strong enough light, your shadow bunny would be racing across the sky faster than the speed of light -- and the crazy thing is, you'd be correct! The shadow (absence of light) can move arbitrarily fast. But the light itself is moving at its normal constant speed from the flashlight out into space, perpendicular to the travel of the bunny, like a garden hose spraying water. The time it takes for the shadow to even begin to move is governed by the speed of light. No information can be communicated faster than light because the light travels at the speed of light to illuminate the places where the shadow isn't.

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  • [–] 4 points 5 months ago (8 children)

    Very eloquent explanation. The one glitch I must point out is that the shadow (or absence of light) can't move faster than light, because the shadow is information and information can't travel faster than light. If it could, you could use a sequence of shadows, coded by length and spacing, for FTL communication.

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  • [–] 14 points 5 months ago

    The shadow moving is more akin to bandwidth of transmission rather than speed of transmission. You still have to wait for the photons (so speed of light) for the information to arrive, even if the "speed" of the shadow appears FTL.

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  • [–] 4 points 5 months ago* (6 children)

    The shadow has no FTL information here. Watch https://youtu.be/JTvcpdfGUtQ

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  • [–] 2 points 5 months ago (5 children)

    Ok I watched the video and I get that no information is travelling FTL. "Speed of darkness" is misleading tho, because the light at the shadow's edge has the same "speed" as the shadow.

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  • [–] 1 point 5 months ago (4 children)

    The edge of the shadow can move across the surface of an object an essentially infinite speed. That's the speed of dark

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  • [–] 1 point 5 months ago (1 child)

    And the edge of a ball of light created by a powerful spotlight could do exactly the same thing. That video is nothing but sleight of hand style tricks dressed up as the speed of dark. You can recreate every scenario using light to argue light is faster than the speed of light. What you're doing isn't movement at all, period.

    Imagine earth has a ring around it the distance of the moon. You have a powerful laser pointer and rotate 360 degrees while pointing at it. The dot of light "travels" around it at insane speeds. This is what the video argues "dark" or the shadow is doing. But if you think about it for a moment you realise each "dot", whether it's the shadow or the laser pointer, is actually a unique thing, and nothing is actually "moving" at all. Shadows don't move. Ever. They aren't even something. They are just light being blocked.

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    • [–] 7 points 5 months ago

    Explanations why space expands are way more crazier than this.

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    [–] 12 points 5 months ago* (4 children)

    my personal headcanon is that the universe is a giant living being and we are its fundamental particles or some other infeasibly tiny thing

    idk what that has to do with light speed and space-time but you can think of that yourself i guess

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  • [–] 6 points 5 months ago (2 children)

    When I was a kid I imagined that our universe and every galaxy in it make up a single atom in another, much larger universe.

    That much larger universe, in turn, is also a single atom in a much larger universe. And so on..

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    • [–] 5 points 5 months ago

    That's so no matter how much knowledge we gain we can never escape the bad place to kill the Demiurge.

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    [–] 5 points 5 months ago (1 child)

    I remember finding out the shape of space isn't a vast plane of emptiness, but more of an ever growing sphere and that messed me up.

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  • [–] 1 point 5 months ago*

    You also need to consider what the things inside it look like to you or anyone else. The observable universe is the volume inside which light can reach us here on the earth... technically it's different for everyone because we're all in a slightly different position, making everyone the centre of the universe, but in terms of the scale of the universe, that's irrelevant levels of accuracy and you can safely state that everyone on earth is in the same place. Now because space is expanding and carrying stars and galaxies with it, those galaxies will eventually pass the point where their light could travel for an infinite time and never reach us, in other words, they would pass beyond the edge of our observable universe. Eventually, given enough time, all that will be left in the night sky (long after the earth is destroyed) will be our galaxy, and possibly bits of our local group, which are gravitationally bound and would hold their relative positions as space expands around them.

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    • [–] 8 points 5 months ago (1 child)

    The speed of dark is faster than the speed of light

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    • [–] 3 points 5 months ago* (last edited 5 months ago) (6 children)

    Since nothing can move faster than the speed of light doesn't it also mean that the universe cannot be expanding faster than 2c either?

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  • [–] 7 points 5 months ago (5 children)

    Not necessarily.

    The expansion of the universe here doesn't necessarily mean matter moving faster than light.

    Think of the universe as a 3+1 dimensional ballon - specifically, the 3D space we occupy is the 2D surface of the balloon. As you blow air into the ballon, that 2D space expands.

    Now, it's a simplistic example mainly because we're three dimensional beings and thus can't easily wrap our heads around a 4D space where one of the surfaces is three dimensional. You run into the same issue as e.g. trying to visualise a tesseract (a four dimensional cube). So a balloon has to do.

    And since this expansion of our universe technically happens outside of it, the general laws of physics - such as the speed of light - do not apply.

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  • [–] 1 point 5 months ago (4 children)

    That's what I meant. Since matter isn't moving at the speed of light, if we assume the universe expansion is due to the movement of its edge objects, then it cannot expand faster than 2c. If the expansion is happening for a different unrelated reason than the edge objects ofc that's something else

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  • [–] 2 points 5 months ago (3 children)

    Your presumption that there’s an “edge” is at fault here. Consider the surface of the ballon (or rather- a bubble) - it’s continuous, just like our universe. And that’s why it’s hard to explain how a 3D space can expand seemingly without a center point - because said center point is not within the constraints of this 3 dimensional space, just like how the center of a balloon or bubble is not on the two dimensional surface but in the center.

    so just like the surface of an expanding bubble, the expansion of our universe doesn’t happen in a plane we can conceptualise easily - it’s a 4 (or possibly more!) dimensional expansion, of which we are just the surface, therefore the expansion appears as if everything literally drifted away from everything - which should be impossible in a 3D space but not when you add a fourth axis.

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  • [–] 1 point 5 months ago (2 children)

    I don't know much about astrophysics, but it seems to me the analogy breaks down. Unlike a balloon, the universe does not move on a medium, so the only way to surmise it's size is by its edges (i.e. the objects at its farthest edges). So the important thing here is how fast those edges move (the dots, on the balloon) which can never be higher than the speed of light. What am I missing?

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  • [–] 2 points 5 months ago (1 child)

    You're still missing the 2D to 3D translation...

    Think in two dimensions. The surface of the balloon is the two dimensions - X and Y axes. The "medium" (the rubber of the balloon) is the fabric of the universe.

    The two dimensional space - much like e.g. the surface of the Earth - has no edges. When the balloon expands (on the third dimension, which the surface dwellers are unaware of), all the surface notices is that any two or three or N points have gotten further from each other. The size of this 2D plane thus can be described by a single dimensional number - the circumference of the balloon (aka "how long does it take to get back to the starting point in the 2D space if you go in any direction).

    You need to extrapolate this continuous 2D surface on a 3D object to a 3D surface on a 4D object. In a four dimensional space, our universe has a four dimensional volume it consumes - but in 3D, it's effectively infinite (curving into itself, much like the surface of the balloon), but also expanding (everything is being further and further from each other).

    To grasp this I'd recommend you read the book Flatland by Edwin Abbott - it's a 140 year old study in the format of a novel, on how beings from an N spatial dimension plane would "see" and interpret a being from an N+1 spatial dimension (in this case, 2D beings, like a square, seeing 3D being, a sphere, intersect with its 2D plane). Mind you it's also a social satire so you'll find a ton of social commentary of the Victorian era Britain, but the core conceptualisation is there - an N spatial dimension being will always have trouble visualising an N+1 dimension.

    So again, in our 3 dimensional plane, the universe has no edges, it's infinite, yet expanding. Just like how the surface of a balloon or bubble has no edges, or how the surface of the Earth has no edges - but in a 3D space you can create a bounding box to define its size. Our 3 dimensional universe is essentially the surface of such a 4D bubble, but that fourth dimension is outside of our universe therefore it can't easily be measured directly. Just like how a dot on the surface of the balloon couldn't measure the 3 dimensional space of the balloon, only by inference of the expansion, theorise that it actually exists in a 3 dimensional system but is limited to the 2D surface of said balloon, and infer its mechanics based on the expansion of space between any two points on the surface.

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  • [–] 1 point 5 months ago

    Well, ok I'm afraid I'm really out of my depth here. It seems to read like the universe is expanding due to an unknown force acting on the 4th dimension (like the air coming in the balloon), but I can't imagine what that would be. I always understood that the universe expansion is simply leftover momentum from the big bang

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