Memes

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.

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.

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

All we are going to die?

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

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.

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?

no

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.

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?

It's 3.26 lightyears.

just more space between

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

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.