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.
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
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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.
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.
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.
courtney you are going to invent rocket ants knock it off
Didn’t get it but saving this so when i grow older I’ll see it again and think for the logic behind it… 🗿
But space contracts at close to light speed,so your analogy isn’t perfect, right?
No, time contracts, not space.
WHOS BLOWONG UP THE BALOON AND WHEN WILL IT 💥
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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.
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!
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.
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
Cool, that’s a good explanation, thanks
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.
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
And Men in Black.
Explanations why space expands are way more crazier than this.
The speed of dark is faster than the speed of light
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.
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.
Well duh. When a thing moves away from another thing, that is moving at the speed of light, at the speed of light, you have speed of light time two!
This explanation is the wrong intuition for why space can expand FtL. It’s an understandable one to infer, but the balloon one further down is correct and the one most commonly used by cosmologists for a lay audience.
Our current understanding of recessional velocity works by Hubble’s law, and that linear equation imposes no such 2x cap.
You still have one speed of light, that’s the Lorentz transformation
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.
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.
Nothing within the known universe moves faster then light, but the universe itself expands faster then light travels within it.
That’s so no matter how much knowledge we gain we can never escape the bad place to kill the Demiurge.
We should probably use the word “growing” instead of “expanding”, would that be easier to follow 🤔
no
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.
Nope!
Information can only travel at the speed of light.
During my undergraduate CERN did this experiment (a decade ago now).
And they had the shocking result of the second wave function collapsed faster than c.
That was until a clock was found to be loosley connected and caused a timing error, that would account for the slower than c speed.
Information can only travel at the speed of light.
I like the general term being used nowadays instead of “the speed of light” - the speed of causality; which is nice because it fits neatly into E=mc2.
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
Lovely how xkcd seems to have the answers to life and its mysteries.
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
First question: two reasons that wouldn’t work: the stick would just break, obviously, but if it was a super duper stick, the torque required to accelerate the end past the speed of light is directly related to how long the stick is, so any increase in speed from a longer stick will be offset by the need to apply more force at your end. Therefore the energy required to flick a stick to the speed of light does not depend on the length of the stick, you are simply creating a reverse lever of sorts. It’s still an infinite energy requirement, assuming the stick has mass.
The second question is a lot easier. The light is traveling directly away from you at all times, there is no sideways motion.
It’s actually simpler: the stick will deform because whatever movement you do travels across the stick at the speed of sound of the material the stick is made out of.
Why does it matter how long it takes for the torque to travel down the stick? The question was about the speed of the tip in the orbital direction, not the speed of the wave in the radial direction outward.
I see your point. Still, it shows there’s no such thing as a “super duper stick” because there’d be shearing forces pulling the atoms apart faster than they can move together.
Yeah that’s the boring answer, it would just break apart. But even without physical limitations, mass has the property that it can’t be accelerared past c with a finite amount of energy, and I think it’s interesting to see why that limit is more fundamental than the structure of matter. No matter how you mess with forces using simple machines, the energy calculations always come out the same.
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
