What happens when you accelerate to a speed at which a photon with a wavelength as large as the observable universe (in the world frame) gets blueshifted to a wavelength shorter than the Plank length in your frame of reference?
Relativistic Spaceship
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Re: Relativistic Spaceship
#112Earlier quoted context omitted.
One gee over the course of months is insane . Even if you converted the entire "fuel" reaction mass directly into momentum, you're still carrying tens or hundreds of thousands of tons of fuel for any remotely habitable spacecraft. And no engine has perfect mass conversion. Matter-Antimatter has been simulated to be maybe sixty percent efficient, fusion is around 17%, nuclear pulse propulsion a surprising 7%, fission…
In the book series The Expanse, that was pretty much the only unrealistic technology that the humans had, which allowed them to colonize the solar system. Sure, there was some might-as-well-be-magic alien stuff later in the book, but by page 1, humans have colonized the solar system, purely with a hand-wavy engine that can generate sustained thrust without needing tons of reaction mass and without turning your exhaus…
No, the exhaust port definitely was an unimaginable hell cannon. The characters spoke several times about slagging a ship or a surface base in their drive plume.
Re: Relativistic Spaceship
#113Earlier quoted context omitted.
You can’t “get to” light speed, that’s one of the big punchlines in relativity. If you pick an acceleration equal to the acceleration we experience on Earth (aka 1g, aka ~9.8m/s^2), you hit relativistic speeds (speeds at which you need to take into account the effects of relativity to do anything) surprisingly fast. On the order of hundreds of days. So, it is not really a matter of safe acceleration on a long space t…
> Instead you have to worry about the actual speed you are traveling at That's the other big punchline in relativity: There's no one "actual speed" because that implies that there is a single "important" frame of reference wherein those atoms are floating around waiting to be hit by a spaceship.
I’m not sure I’d call that a punchline of relativity; the idea of frame of reference is also part of the classical model.
Re: Relativistic Spaceship
#114Beautiful! For the comments saying we "just" need to maintain a 1G acceleration, should point out that as the ship approaches the speed of light, its mass increases [0]. And as the mass increases, so does the thrust required to maintain that acceleration. So that engine better be able to tap into some magical energy source, otherwise it can't maintain the acceleration at the higher speeds. :) [0] https://en.wikipedia…
The last time I studied special relativity was a while ago, but I think your mass only increases in other frames of reference.
If, for example, we consider the speed of your ship from the point of view of someone left on earth, then your ship should appear heavier from that person's perspective as you accelerate. But from your point of view, you still weigh the same, and so does your ship. In fact, you would see earth going through the dramatic "weight gain".
Re: Relativistic Spaceship
#115Earlier quoted context omitted.
One gee over the course of months is insane . Even if you converted the entire "fuel" reaction mass directly into momentum, you're still carrying tens or hundreds of thousands of tons of fuel for any remotely habitable spacecraft. And no engine has perfect mass conversion. Matter-Antimatter has been simulated to be maybe sixty percent efficient, fusion is around 17%, nuclear pulse propulsion a surprising 7%, fission…
> As an SF writer, it's pretty interesting, though, to think of the weird shapes a society would take when your astronauts are outliving entire civilizations. I guess this all depends on how you define simultaneity. Say I got on a relativistic rocket traveling near c and colonized Planet X in 10 years ship time and say 20,000 years Earth time. I put up my TV antenna as soon as I land, and I'd still be receiving Earth…
That's not how it works. If the planet is N light years away from earth, the transmissions you receive would be those sent 20000-n years ago. along the way you'd get most of the messages sent during the 20k years as very red-shifted light, and extremely rapidly from your pov.
Re: Relativistic Spaceship
#116I accelerated to 100%c, but then nothing happened. It seemed like no time passed and I didn't go anywhere. Someone help?
Re: Relativistic Spaceship
#117Earlier quoted context omitted.
I suppose you would also have to worry about surviving the trip - every atom in the interstellar medium would damage your ship, likely penetrating the entire way through, and electromagnetic repulsion would only work with charged particles.
Unless you could somehow make an Alcubierre warp drive. Of course…even if that was possible, it’s conjectured that the colonists already at your destination won’t appreciate you boiling the atmosphere when you hit them with blue shifted radiation. https://www.universetoday.com/93882/warp-drives-may-come-wit...
> Unless you could somehow make an Alcubierre warp drive.
Even if you can make it, even though it's theoretically possible that the warp bubble could move through space faster than the speed of light, it's a separate and completely open question as to how you might actually get it to move that fast to begin with.
Re: Relativistic Spaceship
#118Earlier quoted context omitted.
I wonder what is a safe acceleration to get to light speed for long periods without hurtin too much
You can’t “get to” light speed, that’s one of the big punchlines in relativity. If you pick an acceleration equal to the acceleration we experience on Earth (aka 1g, aka ~9.8m/s^2), you hit relativistic speeds (speeds at which you need to take into account the effects of relativity to do anything) surprisingly fast. On the order of hundreds of days. So, it is not really a matter of safe acceleration on a long space t…
dumb question - why does going faster make it more likely you encounter fast protons? couldn’t protons in any reference frame be going quite fast relative to you?
Re: Relativistic Spaceship
#119Earlier quoted context omitted.
Its remnant, its echo, or just the big bang, however you want to see it.
A whole lot happened between the big bang and the formation of the CMB 400.000 years later.
You’re driving and see a huge patch of the fog suddenly turn red, I would argue you’re seeing break lights not fog. But that gets into definitions not just physics.
Similarly, the CMB is energy from the Big Bang as last scattered ~380,000 years later. IMO, that’s the Big Bang, but reasonable people can obviously disagree.
Re: Relativistic Spaceship
#120Earlier quoted context omitted.
I suppose you would also have to worry about surviving the trip - every atom in the interstellar medium would damage your ship, likely penetrating the entire way through, and electromagnetic repulsion would only work with charged particles.
Every proton would have the energy of a baseball. It's bananas. Granted, space is really empty, but it's not that empty, somewhere around a hundred atoms per cubic meter. Your ship might look like a very, very long shooting star. Probably dialing the speed down a touch would be worth it for whatever your shielding material is, but who knows? We're talking miracle engines here. I think in the "Valkyrie" ship-on-a-stri…
why are protons more likely to be closer to rest relative to earth than relative to the fast spaceship?