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Shadows can move faster than light.
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.
We should probably use the word “growing” instead of “expanding”, would that be easier to follow 🤔
no
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!
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.
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.
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.
Explanations why space expands are way more crazier than this.
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 💥
Didn't get it but saving this so when i grow older I'll see it again and think for the logic behind 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.
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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?
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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
just more space between
Space out of thin air... tell me, mate, can I sell it?
NFT's sold, so probably yes
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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Well, nothing (with nonnegative mass) can move faster than light through space. Space itself can do whatever it wants to.
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Nothing within the known universe moves faster then light, but the universe itself expands faster then light travels within it.
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this post was submitted on 25 May 2026
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