> The macro evidence in that if FTL were possible it makes it that much more unlikely that we haven't detected starfaring life.
I don't think this is a great argument. Even with FTL the galaxy (not universe) is huge. Let's just say you can go 2x (warp factor 1.25) it would still take more than 2 years to reach Alpha Centauri (our closest star, 4.37 lyr). Even at 8c (Warp 2) it would still take >6 months. At 100c it is 2 weeks. The energy to travel these different speeds presumably does not scale well and so the difference between 2c and 1000c is going to be different level of civilizations[0]. The Milky Way is 2 million light years in diameter. There's about 1000 stars within 50 light years. Here's a list of stars <5 parsecs (16 lyr)[1] or within 5 days at 1000c or 0.0008% of the Milky Way. There could be extensive networks of trade and travel with FTL civilizations and we'd probably never detect them. These routes would still be fairly local and if they aren't around us then we would have no chance of seeing them. This is basically peoples in the Western Hemisphere trying to observe people in the Eastern Hemisphere when neither civilizations have the ability to cross the ocean nor see across it to a reasonable resolution.
I think a lot of people miss how huge the galaxy is (let alone Universe). Nothing is accessible without FTL. FTL is _necessary_. That, or immortality, or generational ships. The problem is that these numbers are so incomprehensibly large that we think they are magnitudes smaller than they actually are.
However big you think the galaxy is, it is actually bigger.
I don't think it's fair to say "or immortality, or generational ships." You can make a one way trip, sometimes, but you can't meaningfully communicate. FTL is necessary or the universe is kind of boring on a grand scale.
What I'm saying is that you're not going to travel a meaningful distance in the Milky Way (as in percentage) within several lifetimes. Longer life or generational ships are absolutely necessary, even at high speeds and time dilation.
It's not boring, it's just too big and therefore too slow for our tastes. If we lived 5,000 years, taking a 100 year trip to Alpha Centauri might not seem so bad. I think extending lifespan like this is more likely than building an FTL drive.
My concern is the mismatch between the timescale we communicate with people and the timescale of the trips (minutes or hours vs centuries). It would be such a massive transition during your trip that it is hard to adequately describe it.
In the past information had to travel by people or pigeon (some sort of physical movement). Realistically this is communication happening faster than travel does. Currently we have the inverse, where information is faster than travel. This should similarly happen in this FTL world because of Ansbiles and that you can not just send ships full of people FTL but information (and presumably more easily). So I think the only difference is that the travel time is scale. Right now there's nowhere it takes months to travel and we can communicate instantly. In this scenario we actually have a mixture of past and present. We can maintain near instant communication but maximal traveling distance is years instead of days.
The Milky Way is only about 100K to 200K light years in diameter; the 2 million diameter includes hypothetical dark matter.[1] If it takes a thousand years on average to spread civilization out by another light year, that's as little as 100M years to spread from one side of the normal-matter galaxy to the other. That's less than 1% of the age of the Milky Way.
Assuming exponential growth, an alien civilization could easily have populated the galaxy. Or heck, octopuses are pretty smart and have been around for 150 million years, if they were land animals and figured out fire they'd probably rule the galaxy already.
I don't think this is a great argument. Even with FTL the galaxy (not universe) is huge. Let's just say you can go 2x (warp factor 1.25) it would still take more than 2 years to reach Alpha Centauri (our closest star, 4.37 lyr). Even at 8c (Warp 2) it would still take >6 months. At 100c it is 2 weeks. The energy to travel these different speeds presumably does not scale well and so the difference between 2c and 1000c is going to be different level of civilizations[0]. The Milky Way is 2 million light years in diameter. There's about 1000 stars within 50 light years. Here's a list of stars <5 parsecs (16 lyr)[1] or within 5 days at 1000c or 0.0008% of the Milky Way. There could be extensive networks of trade and travel with FTL civilizations and we'd probably never detect them. These routes would still be fairly local and if they aren't around us then we would have no chance of seeing them. This is basically peoples in the Western Hemisphere trying to observe people in the Eastern Hemisphere when neither civilizations have the ability to cross the ocean nor see across it to a reasonable resolution.
I think a lot of people miss how huge the galaxy is (let alone Universe). Nothing is accessible without FTL. FTL is _necessary_. That, or immortality, or generational ships. The problem is that these numbers are so incomprehensibly large that we think they are magnitudes smaller than they actually are.
However big you think the galaxy is, it is actually bigger.
[0] https://en.wikipedia.org/wiki/Kardashev_scale
[1] https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brow...