In the same way that two cars driving away from each other at 60 mph have relative speeds of 120 mph with regard to each other, two bodies moving away from each other at less than the speed of light have relative speeds exceeding it. Everything in the universe is moving away from everything else and sometimes at relative speeds that exceed the speed of light. Nothing is individually exceeding the speed of light in absolute terms.
I fucking hate that aspect of Special Relativity when I did l A-Level Physics (wait, shouldn’t that be “Physic” in the US to go with “Math”?). Two spaceships head off in opposite directions at light speed - from the frame of reference of each spaceship, the other is moving away at C, not 2C, because the Universe would rather slow down time itself than let anything move faster than its stupid precious C!
Wait does that mean theoretically one thing can slow another down by just being an observer if it is also moving in the opposite direction?
It’s pretty complicated and it’s been a while since i read the layman’s-terms no-maths explanations, but think of it like driving
You’re in a car looking at another car which is driving at the same speed on s road which is parallel to you. You’re both going to look like you’re driving at the same speed and travelling the same distance
Now say that rather than being parallel the roads are at an angle to each other. Say 45 degrees. Now when you look at the other car, even though its Speedo will say the same as yours it’ll look to you like it’s going slower and it’ll fall behind you. After a while you won’t be able to see it out of the drivers side window and will have to look through the back seat window and then the rear window to see it
And the experience in the other car will be the same - they’ll see you as going slower and falling behind them
Nobody’s speed has actually changed, it just looks different from each car’s perspective
If you can mentally change “difference travelled” to “time passing”, then that’s how to conceptualise it
That’s intuitive but actually completely wrong. There is no “absolute” reference frame, and nothing can move faster than light in any relative reference frame.
The only thing that gets around that is the expansion of space itself. It’s not that the objects are moving away from each other, it’s that the distance between them is expanding, causing them to become farther apart.
The best analogy is to picture an ant crawling on the surface of an expanding balloon.
Okay but the ant can still only go at the speed of ant.
Exactly! That’s why we have a concept of observable universe.
As the universe expands (think of it not as ants moving, but more space created between ants as balloon gets inflated), at some distance away from us it starts doing so faster than light.
The light, however, can only travel at, well, the speed of light. As such, we will never see or reach anything that is beyond this light speed horizon. And as the expansion of the universe speeds up, more and more objects that we can still observe will disappear beyond this point.
Relative speeds also cannot exceed the speed of light. Since there’s no absolute reference frame, if this were possible it would be no different than exceeding the speed of light on “absolute” terms. Once you get up to speeds where this would matter, funny dilation effects that I’m too dumb to understand would prevent this.
Cars are not driving away from each other at more than the speed of light relatively. The road is stretching faster than the speed of light.
Yeah, but wouldn’t this lead to the cars perceiving each other as moving faster than light?
No, because the space is expanding faster than light, the light can’t bridge the gap and so you and the other car simply can’t perceive each other at all.
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. 😌
We should probably use the word “growing” instead of “expanding”, would that be easier to follow 🤔
no
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.
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.
As far as I know, not even that is certain. I read something about other topologies, like a donout shape or even higher dimentional topologies being plausible as well. Interesting rabbit hole but really makes you question our how we view our reality.
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.
WHOS BLOWONG UP THE BALOON AND WHEN WILL IT 💥
Thanks for that that’s actually a really helpful analogy.
I mean i still dont understand. Brain hurty. But thanks anyway
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).
All we are going to die?
Yes
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)
Finally, some good news.
https://en.wikipedia.org/wiki/Timeline_of_the_far_future breaks this down.
Current data suggest that the universe has a flat geometry
Holyshitholyshitholyshit don’t tell flat earthers
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.
Yes, and actually right now relatively speaking.
Didn’t get it but saving this so when i grow older I’ll see it again and think for the logic behind it… 🗿
This is a truly great explanation. One worthy of Feynman. Physics degree?
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.
On todays episode of: University degree or autism?
The space between atoms starts to expand faster than the speed of light. Well i guess that is the universe fucked.
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.
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.
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.
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.
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!
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?
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 <some extremely short time> 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.
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…
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.
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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courtney you are going to invent rocket ants knock it off
But space contracts at close to light speed,so your analogy isn’t perfect, right?
No, time contracts, not space.
Explanations why space expands are way more crazier than this.
Shadows can move faster than light.
Only on the Discworld
No they can’t, because they aren’t moving at all. That vsauce video pisses me off so much and I’ve debunked it more than once over the years, but suffice to say, you could claim light moves faster than light using the same logic he uses for shadows/darkness.
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.
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.
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.
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.
The shadow has no FTL information here. Watch https://youtu.be/JTvcpdfGUtQ
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.
The edge of the shadow can move across the surface of an object an essentially infinite speed. That’s the speed of dark
Yeah I get it. Do you get that the light around the shadow, that isn’t part of the shadow, is moving at the same “speed” - so it’s not the speed of “dark”. It could be dark, it could be red light, blue light, full white, any color or lack of color.
That’s the point yes
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.
Congrats you get it
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?
Understanding this is the easy part imo
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.
No, you completely understand quantum physics, you are one of the elite.
But in the analogy I don’t think we know what the air in the balloon is, we call it expansion. But I don’t know enough to say anymore
We are the dots on the surface of the balloon. Things really far away seem to be moving away from us. Hopefully we can figure out what gravity is because that would have a lot of gravitas I dunno whatever
I’m fairly certain that in the balloon example metaphor, we are two dimensional creatures on the surface of the balloon
Space time itself is expanding which means I will now blow up soon. Yay!
Yeah, when you put the dimensions implication in it it starts making a bit more sense - implying that we’re two-dimensional and the third dimension inside the balloon is the things that we don’t fully comprehend (yet).
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?
Great analogy, and yeah the “ish” is the fun part!
The fun of justifying a reference frame outside the universe. Sorry I’m getting a headache.
You can explain but don’t but criticize you are idoltarer and are in degenerate dharma like all Christians nowadays
besides the expansion of spacetime which is the correct answer, there’s also nothing keeping two objects from traveling in opposite vectors each at 60% c. Frame of reference matters too
No, spacetime doesn’t expand faster than light at any point. Its just that as you accumulate the new growth over a long distance, the farther objects appear to move away faster than light from our position.
The very short, very bastardized version is that as objects move at speeds closer to the speed of light, the way everything else around them appears to be shaped and moving changes. A “stationary” object you pass seems less long than it should in the dimension parallel to your travel. The net result is that however two objects are moving relative to each other, their own speeds warp their experiences of the universe such that nothing else is observed to be doing something “illegal”.
There actually are things keeping that from happening but I don’t want to get into it
I may be wrong, it’s been a while since I looked into relativity. But I think it’s possible from an outside perspective to see 2 objects that have a velocity relative to each other that is faster than the speed of light.
If 2 spacecraft travel in opposite directions at 60% of the speed of light from the earth it would appear that they are traveling away from each other faster than the speed of light. From either ship it would not appear that the other ship was traveling faster than the speed of light however.
Yeah that’s correct. If things couldn’t move apart from each other faster than the speed of light from a 3rd party observers perspective, light itself would make no sense. Either all light would actually be travelling at half the speed of light, or half the light would be frozen.
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
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
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.
just more space between
Space out of thin air… tell me, mate, can I sell it?
NFT’s sold, so probably yes
Beautiful! That’s the kind of perfect explanation I was trying to come up before giving up and just saying the expansion doesn’t have a speed because it isn’t motion, which is only partially correct lol.
This guy expands!
Well, nothing (with nonnegative mass) can move faster than light through space. Space itself can do whatever it wants to.
Well, the thing space is moving into and across. Or the nothing.
I don’t know why maybe the painkillers are speaking but I have to ask, does farts count as negative mass?
I’ll take my leave…
ᕕ(ᐛ)ᕗ
Okay … enjoy your painkillers, man.
Incoming vibe killer: no, farts do not count as negative mass. They do in fact have positive mass. You will weigh ever so slightly less after farting. And, in theory, if you were in a frictionless environment, you could propel yourself by farting, because the fart’s mass would act as a reaction mass and propel you like a (very weak and stinky) rocket.
Negative mass would be a very weird thing that breaks physics in a lot of ways, and probably isn’t physically possible in the first place. Allowing faster-than-light travel is only one of many stupid ways negative mass would horribly wreck all known physics.
Thank you for the explanation.
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
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…
Dark Tower did the same bit as well
And Men in Black.
I have had thoughts like that before! Especially since at school the atomic model that was taught looked like a little galaxy (which I now know is inaccurate) and it seemed like going smaller or going bigger just repeated similiar patterns, so to say.
“As above, so below” is a pattern that’s almost universally recognized for a reason. The galaxy atom model may not be accurate, but lots of things in the world rhyme at different scales.
Thank you! I used this weird thought to wipe my brain from other weird thoughts, it needed that.
Nothing within the known universe moves faster then light, but the universe itself expands faster then light travels within it.
The speed of dark is faster than the speed of light
Light thinks it travels faster than anything but it is wrong. No matter how fast light travels, it finds the darkness has always got there first, and is waiting for it.
Terry Pratchett
That’s so no matter how much knowledge we gain we can never escape the bad place to kill the Demiurge.
