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I used to be fascinated with the UFO reports and such as a kid. However, I grew up, and learned physics. And then later I learned about things like Molecular

I used to be fascinated with the UFO reports and such as a kid. However, I grew up, and learned physics. And then later I learned about things like Molecular Nanotechnology. Aliens, as popularly conceived, have not been here, and will not be coming here. Why? I'll explain. Space is big. Like, really big. The distance to the nearest star system is 4 light-years away. Even for a small object, it takes an enormous amount of energy to get going at a "reasonable" speed, like at some fraction of the speed of light. For an example of a more reasonably-sized object, Voyager 1 would take 70k years to get to the closest star system (4LY away) if it was headed in the right direction. But then you have to stop! If you accelerate up to 0.1c (very fast), you have to decelerate to arrive at your destination. This is where the rocket equation kills you. Even with super-mass efficient ion drives (which with our current technology provide very low thrust), accelerating your spaceship to a reasonable speed, and then have enough delta-V to stop at the destination requires an even more crazy amount of energy. If any aliens are headed to our solar system, we'd see their drive flairs from a long way out. The most efficient system is to use a light sail (really, a laser sail). This is so you don't have to carry all that reaction mass with you, thus bypassing the rocket equation. And then there's a trick where you detach most of your sail, allowing it to reflect light back towards the ship for the deceleration half of the trip. But again, even for a small (like 1kg) payload, this requires a stupendous amount of energy. And we'd see them coming because they'd be shining a big, big laser in our direction. There are also Bussard ramjet drives, and other speculated technology, but these would all likely be slower because of the mass required to build it. Now simply flinging out a bunch of von Neumann replicators out in every direction would be much less obvious (though very slow), until the space dust starts building infrastructure in our solar system... but that's a talk for another day.

em3rgent0rdr 9y ago
But maybe the UFO are really old machines (like millions of years old) in which case they can take all they time they need to travel and decelerate, such that wouldn't produce drive flairs.
- ansible 9y ago
  Anything is possible, but that doesn't seem likely. It is helpful to think of what would aliens want from us that they can't get at home. Raw material, like in the mini-series V, Oblivion, Uplift War trilogy, etc? It is too expensive to ship matter anywhere. If you need a lot of it for a construction project, you'd be better off heading to the galactic core. Maybe they want our cultural uniqueness? But they could easily simulate many virtual worlds with different starting conditions, and poke around those without leaving the comfort of home. That would be much easier, especially after they get bored with humans. And if they have advanced molecular nanotechnology, it isn't just waiting millions of years for results. They are likely running at a much higher "clock rate" than we are now. You can run an uploaded mind much faster than a biological one. So these hypothetical aliens would instead be waiting billions of years of subjective time for their probes to find something interesting.
  - brango 9y ago
    Maybe they just want to study us. If we discovered an alien race it'd be pretty interesting to watch them evolve. It'd be just like the fun parents have seeing children grow up.
    - ansible 9y ago
      Maybe they just want to study us. If we discovered an alien race it'd be pretty interesting to watch them evolve. It'd be just like the fun parents have seeing children grow up. Maybe, but I find that unlikely. If they do want to pursue those sorts of activities, then can do much more, much faster while closer to home. Why settle for observing one naturally evolved species, when you can make dozens (or thousands) of your own?
brango 9y ago
Unknown unknowns mean you don't know if there's a way to make fast, long distance travel feasible. From a Newtonian perspective quantum physics sounds like a complete joke. There are undoubtedly other discoveries yet to be made. I can certainly countenance that future scientific advancements could make what we think of today as being impossible as being possible without violating the laws we have discovered.
- ansible 9y ago
  While there are definitely gaps in our understanding, the standard model of physics is one of the best scientific theories... ever. So we don't yet have a grand unified field theory, but for what we do understand, at reasonably attainable energy levels, there just isn't room to jam in some sort of faster-than-light communication or faster-than-light travel. If you look at how it all fits together, any sort of magic like that seems highly unlikely. Nothing we've observed in the sky, dating back billions of years, suggests FTL either. Until I see something that can even hint at FTL, I'm completely discounting it.

em3rgent0rdr 9y ago

But maybe the UFO are really old machines (like millions of years old) in which case they can take all they time they need to travel and decelerate, such that wouldn't produce drive flairs.

ansible 9y ago
Anything is possible, but that doesn't seem likely. It is helpful to think of what would aliens want from us that they can't get at home. Raw material, like in the mini-series V, Oblivion, Uplift War trilogy, etc? It is too expensive to ship matter anywhere. If you need a lot of it for a construction project, you'd be better off heading to the galactic core. Maybe they want our cultural uniqueness? But they could easily simulate many virtual worlds with different starting conditions, and poke around those without leaving the comfort of home. That would be much easier, especially after they get bored with humans. And if they have advanced molecular nanotechnology, it isn't just waiting millions of years for results. They are likely running at a much higher "clock rate" than we are now. You can run an uploaded mind much faster than a biological one. So these hypothetical aliens would instead be waiting billions of years of subjective time for their probes to find something interesting.
- brango 9y ago
  Maybe they just want to study us. If we discovered an alien race it'd be pretty interesting to watch them evolve. It'd be just like the fun parents have seeing children grow up.
  - ansible 9y ago
    Maybe they just want to study us. If we discovered an alien race it'd be pretty interesting to watch them evolve. It'd be just like the fun parents have seeing children grow up. Maybe, but I find that unlikely. If they do want to pursue those sorts of activities, then can do much more, much faster while closer to home. Why settle for observing one naturally evolved species, when you can make dozens (or thousands) of your own?

brango 9y ago

Unknown unknowns mean you don't know if there's a way to make fast, long distance travel feasible. From a Newtonian perspective quantum physics sounds like a complete joke. There are undoubtedly other discoveries yet to be made. I can certainly countenance that future scientific advancements could make what we think of today as being impossible as being possible without violating the laws we have discovered.

ansible 9y ago
While there are definitely gaps in our understanding, the standard model of physics is one of the best scientific theories... ever. So we don't yet have a grand unified field theory, but for what we do understand, at reasonably attainable energy levels, there just isn't room to jam in some sort of faster-than-light communication or faster-than-light travel. If you look at how it all fits together, any sort of magic like that seems highly unlikely. Nothing we've observed in the sky, dating back billions of years, suggests FTL either. Until I see something that can even hint at FTL, I'm completely discounting it.