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.
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.
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?
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.
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?
Understanding this is the easy part imo
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
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
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
This guy expands!
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.
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
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.
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.
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.
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
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.
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
Thank you! I used this weird thought to wipe my brain from other weird thoughts, it needed that.
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
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
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”.
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.
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.
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.
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.
A shadow can move faster than light too.
We should probably use the word “growing” instead of “expanding”, would that be easier to follow 🤔
no
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?
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.
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
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.
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?
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.
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
Fuck it, question that I had since 10 years old.
if I have a very long stick, and I flick it. what would happen to the tip? what if a laser pointer is used? at a certain distance, the beam would be moving (sideways) faster than light.
it might work better with a whip rather than a solid stick.
The end of the stick would respond at the speed of sound travelling through the medium of a stick.
As for the laser pointer, the thing that’s moving faster than light isn’t really a moving thing any more than something appearing in a 24fps film is moving, if you know what I mean? It’s just an abstract notion of a moving dot. The light that comes back to you from above isn’t the same light that’s come back to you from below.
Now I wish I had a nice big wall about a light second away and a massive laser to draw things on it.
Bonus: angle the wall so that the left side is a light second and the right side is a light minute away. Alternate the laser on/off.
Good news! We do have a nice big wall about a light second away! Hard to find a laser that’ll make a visible dot on the moon, though
but how will it look like?
for a short scale it’ll be a straight line. but a few light years away? where the abstract dot is moving faster than the speed of light? what shape would you see? definitely not a straight line. and definitely some time issues. like it’ll hit you and then you’ll see it hit other planets you’re left and right?
Think of it like a hosepipe. You’re on the lawn with s long stream of water coming out of the hose. If you flick it quickly it doesn’t stay in a straight line. The beam of water curves as you move.
Because the beam of water isn’t an object. It’s a stream of particles which are constantly being emitted from the tip of the hose
Same thing with a laser beam. It’s a stream of photons being emitted from the laser. If you flick the laser, the photons which have already been emitted will continue in a straight line. Any which are emitted during the flick will head off in a straight line in the direction the laser was pointed. End result:a curved beam
that makes sense, but I’m trying to imagine how that beam would look like a few light years away before it hits you, when it hits you, and after.
Same as the beam of water, but on a much bigger scale and with the curve being much smaller because the things being emitted are so much faster
The Information that the stick has begun to move takes time to travel through the stick. Kind of like bending, but not really.
That’s where things get weird. The tip won’t exceed the speed of light. You could have a section near you moving at the speed of light and the tip will also be moving at c, because c is the limit.
If you were on a train moving at 100mph, and threw a baseball at 50mph in the direction of travel, then the baseball is moving at 150mph. But if you were moving at c and threw that baseball it would not go faster than c.
In fact, everything would move very very rapidly away from the baseball hitting the first air molecule it touches (assuming you yourself have no mass in this scenario).
but from the point of view of the guy throwing the ball, the ball will move away from me at c faster than me. but time experienced by all involved would be a mess
The tip of the very long stick would still move at sub light speeds. Also, the atoms at the far end will not immediately know what your hand is doing at the other. The forces the atoms make on each other also travel at (sub) light speed.
I guess imagining a perfect unbendable stick would break physics somewhere else.
You must define exactly what you mean by unbendable using existing physics.
There may be a different definition that makes a paradox.
Quantum entanglement is faster than light
Nope. Quantum entanglement is when two particles are made to have the same states. Measuring one tells you about the other one in much the same way you can tell what someone you’ve never met before looks like if you’ve seen their identical twin. Also, much like how punching one twin in the face and breaking their nose has no effect on the other twin fifty miles away, doing something to one half of an entangled pair does nothing to the other. In fact, because they’re no longer identical, the particles aren’t considered to be entangled anymore.
Entanglement can be used for encryption, but it can’t be used to transmit data.
Nothing within the known universe moves faster then light, but the universe itself expands faster then light travels within it.
I don’t think it is
