Ask Lemmy

Isn't Venus's atmosphere dense? If so, you could just float a Bespin-like Cloud City on a convenient layer of the atmosphere to avoid the boiling temperatures below and the crushing weight of the air...

I think the closest we will come is detecting radio signals from another species. But like obviously 2 way communication would be almost impossible due to sheer distance.

That's not how it works. You're correct when you say that from your point of view it's Earth's clock going half speed and from Earth's point of view it's your clock going half speed while you're traveling away from Earth (or Earth is traveling away from you, both are equally valid), but that's only true as long as the distance between you and Earth continues to increase at 86% of the speed of light. As you decelerate at your destination your reference frame continuously changes until you're back in the same frame as Earth (or nearly so, we can assume the two stars aren't exactly maintaining their relative positions). While you're decelerating, from your perspective Earth's clock speeds up and goes faster than yours, how much is determined by your rate of change in relative velocity. Earth's reference frame isn't changing (ignoring movement around the sun, galactic center, the great attractor, etc.), so the Earth's perspective on your clock doesn't change, the Earth sees your clock gradually speed up as you "slow down" until it's going the same rate, but never faster. So once you're back in the Earth's reference frame both you and the Earth will agree that your clock advanced 5 years while Earth's clock (and your destination's clock, adjusted for any relative movement between it and Earth) advanced 10 years. This assumes a constant 86% light speed and ignores the time accelerating at departure and arrival so let's assume very fast acceleration so it doesn't change more than a couple days.

Edit: this is all completely ignoring gravity based time dilation from the spaceship climbing out of Sol's well and going down the destination's well and only considers velocity based time dilation. It would be more correct if you only considered two spaceships in a void where one accelerates to relativistic speeds and then accelerates back into the reference frame of the other.

Assuming a mechanism exists that changes the universe from being singly connected to multiply connected (i.e., wormholes exist), it is possible to have wormholes permitting faster-than-light travel without time paradoxes, though some additional restrictions may apply.

We have already shown that wormholes connect across both space and time, so that a trip between star systems could take you hundreds of years into the future, and the return trip takes you hundreds of years back in time. And this is even before we throw in how time slips between planets when considering relativistic time dilation due to different speeds and gravitational potentials.

Fortunately, all the weirdness of different time rates and going backward and forward in time can be ignored by the average person. This is because you never need to go from one world to another, or back, across the vast gulfs of interstellar space. You just take the wormhole between them. All you ever need to worry about is the coordinate frame that goes across the wormhole. When considering this reference frame, you're not hopping all over the place in time. If it takes ten minutes to cross the wormhole between the two planets, when you get to your destination world the clocks will read ten minutes later than they did when you left your departure world. By coordinating their time-keeping across the wormhole network, all of the worlds of the network can agree on a common time to coordinate their activities. This is all travelers ever need to worry about, and they can then ignore all the relativistic weirdness. Your network engineers will still need to keep track of relative time drift and how close a given configuration is getting to a time loop. But unless your protagonist is a network engineer, they can just ignore all that stuff. And, as an author, so can you! Assume your engineers are competent, you have good regulatory bodies and standards institutions, and don't worry about any of this "time travel" that doesn't actually let you cause paradoxes.

source: Galactic Library

The very slow is the issue. Assuming we can reach 10-20% of c, we can reach a couple of nearby stars in 200 years (Wikipedia gives me 50 stars with 30 ly).

200 years is roughly the time from the Napoleonic era from today (Taking an Euro reference). Do you remember what your ancestor were doing during Napoleon Russian campaign or when US purchased Louisiana?

Society changed massively since Napoleon. Over 200 years the society culture of a generation ship would also drastically diverge from ours. Moreover, I can't think of many piece of technology which can keep working for 200 years without a few massive overall.

It makes interstellar travel plausible but not intergalactic.

In theory yes... but the oldest frozen specimen of humans we've found is only a few thousand years old. We don't even know if long term cryogenic reanimation is possible.

Assuming the ship travels at 10x our current capabilities we're still looking at ~8,000 years to reach our closest stellar neighbour at only 5 lightyears away.

Sort of - but there is no reason to think we will ever be able to make something that won't break. Even intersellar is questionable just because the odds of the ship breaking in the time needed are too high.

You are talking about a trip that would last longer than human civilization has existed.