• 3 Posts
  • 162 Comments
Joined 1 year ago
cake
Cake day: June 5th, 2023

help-circle





  • If you’re actually curious, or someone else reading this is, you never can get a rocket, or anything with mass, to the speed of light either, not just faster than it, but you can get arbitrarily close. However, you never notice anything stopping you going faster than your current speed, there’s no point where your rockets stop working or anything, rather, time and space stretch and squeeze such that neither you nor anybody else see you going faster than light. If you have a magic rocket that somehow has infinite fuel and can fire forever, you can actually get anywhere as fast as you want, from your perspective.

    Alpha centauri is famously about 4 light years away, but you can get there in 2 seconds, from your perspective, if you go fast enough. But, everyone on earth will see slightly over that roughly 4 years go by in the time that for you is just 2 seconds. (You’ll see them move slowly too at first, since they’re moving relative to you just as fast as your ship is moving to them, but when you slow down, you’ll see them seem to speed up until you’ll have seen them do 4 years worth of stuff by the time you stop). Meanwhile on your ship, you don’t see yourself crossing that 4 light year distance in less than the allowed time either, because space itself is squished kinda, so that the distance to alpha centauri is shortened to the point that if you’re getting there in 2 seconds, it’s now less than 2 light seconds away, from your perspective, and you’re not moving faster than light to cross that distance in that time. People outside will also see your ship compressed like this too.

    This isn’t just a regular optical illusion either, space and time really are different for the people on and off the ship (and indeed very slightly different for everyone anywhere). Nobody has the “correct” view of the universe, because everyone’s perspective is equally valid.



  • I imagine any explanation of the expansion of the universe for people that are not themselves studying astronomy is going to be simplified in a way that gives the average person the basic idea but not the complete picture to avoid confusion when explaining the concept. Ive not studied astronomy, but I did get most of the way through a physics degree, and know that at least there, a lot ideas are explained in that sort of way to people without much knowledge of the subject, especially the more confusing concepts. I wouldnt be surprised if thats the case for most fields of science. For a different example as an analogy, its common knowledge that you cant move faster than light (ignoring the whole expanding spacetime stuff), but it isnt always explained why this is the case, leading to questions from some people like “what happens if I fly a spaceship to the speed of light, and then turn on the rockets to try to go faster?” which have easy answers or just dont make sense as a question if one has had the behavior of objects at high speed explained, but which seem reasonable enough questions to ask if all youve been told is that the speed of light is just some cosmic speed limit. People cant reasonably blame you for finding an incomplete explanation you’ve been given, well, incomplete, and then asking questions that come to mind as a result.











  • I used to be pretty excited about 3d printed homes, but an argument I’ve seen, that’s made me a lot more skeptical of them, is that much of the work of building isn’t putting up the actual walls, it’s all the wiring, plumbing, installing windows and climate control and insulation and roofing and whatever else like that that turns a building from essentially an artificial cave into a more livable space. A 3d printer that prints you walls out of concrete or whatever is only doing the easy part for you in that case, and not necessarily even in the most efficient or desirable manner. Not to say that the idea of more efficient ways to build housing cheaply isn’t interesting to me, I just think that it’d be something more boring, like a a bunch of improvement to modular prefab construction. 3d printing is an awesome technology, but it’s not a good option for everything