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[-] treesquid@lemmy.world 5 points 1 hour ago* (last edited 1 hour ago)

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.

[-] baconsunday@lemmy.zip 3 points 4 hours ago

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.

[-] in_the_dark_forest@feddit.org 2 points 1 hour ago

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.

[-] Kolanaki@pawb.social 30 points 8 hours ago* (last edited 8 hours 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. 😌

[-] rumba@lemmy.zip 3 points 7 hours ago

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

[-] PhAzE@lemmy.ca 2 points 2 hours ago

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.

[-] MajorasTerribleFate@lemmy.zip 4 points 4 hours ago

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".

[-] GiveOver@feddit.uk 1 points 5 hours ago

There actually are things keeping that from happening but I don't want to get into it

[-] EvilHankVenture@lemmy.world 2 points 3 hours ago

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.

[-] HrabiaVulpes@europe.pub 6 points 9 hours ago

Explanations why space expands are way more crazier than this.

[-] LovableSidekick@lemmy.world 35 points 20 hours ago* (last edited 20 hours ago)

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.

[-] rektdeckard@lemmy.world 26 points 19 hours ago

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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[-] crapwittyname@feddit.uk 16 points 20 hours ago

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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[-] starman2112@sh.itjust.works 29 points 21 hours ago

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

[-] vivalapivo@lemmy.today 4 points 8 hours ago

just more space between

Space out of thin air... tell me, mate, can I sell it?

[-] rumba@lemmy.zip 3 points 7 hours ago

NFT's sold, so probably yes

[-] starman2112@sh.itjust.works 20 points 20 hours ago* (last edited 20 hours 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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[-] EggInDisguise@lemmy.blahaj.zone 212 points 1 day ago

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.

[-] Ichiro_kun@lemmy.world 3 points 7 hours ago

Didn't get it but saving this so when i grow older I'll see it again and think for the logic behind it.. 🗿

[-] capuccino@lemmy.world 32 points 1 day ago
[-] EggInDisguise@lemmy.blahaj.zone 10 points 21 hours ago

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)

[-] WormEmperor@sopuli.xyz 10 points 21 hours ago

Finally, some good news.

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[-] yermaw@sh.itjust.works 51 points 1 day ago

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

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

[-] sp3ctr4l@lemmy.dbzer0.com 1 points 1 hour 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).

[-] mannycalavera@feddit.uk 15 points 23 hours ago

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

[-] EggInDisguise@lemmy.blahaj.zone 11 points 21 hours ago

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.

[-] vaionko@sopuli.xyz 1 points 4 hours ago

On todays episode of: University degree or autism?

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[-] BrazenSigilos@ttrpg.network 3 points 16 hours ago

Nothing within the known universe moves faster then light, but the universe itself expands faster then light travels within it.

[-] Chrobin@discuss.tchncs.de 65 points 1 day ago

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

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this post was submitted on 25 May 2026
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