6 ms·

Something like this strikes me as the most likely Fermi paradox explanation. We will probably eventually find other life, but it will almost always be bacteria

by api 5y ago

Something like this strikes me as the most likely Fermi paradox explanation. We will probably eventually find other life, but it will almost always be bacteria to at most multicellular life on the order of Cambrian era fossils. If intelligence occurs at a rate less than say once per galaxy per billion years, we may never meet ETI. Might find lots of bugs though. Intergalactic travel is many orders of magnitude harder than interstellar travel. The time frames are insane even close to light speed. Over millions of years things fall apart at the molecular level. Building anything that could last that long, even dormant, would be far beyond any technology we can foresee.

cft 5y ago
Even if a galaxy is 10 million light-years away, you can get to it in 1 month of proper (spaceship) time, if you travel fast enough. This is time dilation due to special relativity.
- nefitty 5y ago
  If this is true you just lit a candle in my internal temple of hope lol
  - cft 5y ago
    In the Earth time, the spaceship would take a bit longer than 10m years to reach it, however. Plus the energy required to reach such velocity would probably be more than mass of the Earth if we were to annihilate it.
    - ant6n 5y ago
      Well, accelerating a 100 ton spaceship to 0.99c (assuming some sort of beamed propulsion) requires only 2000 Terawattyears [1]. Of course, to turn 1e6 years into 1 year relative time, one needs like 0.99999999c, one needs 2 million Terawatt years [2], which is a much bigger energy investment, but still not on the order of annihilating the planet. Breaking is gonna be a bitch tho. [1] 100000 kg * (0.99 * c)^2 / sqrt(1-.99^2) in Terawatt Years [2] 100000 kg * ( 0.99999999 * c)^2 / sqrt(1-0.99999999^2) in Terawatt Years
      - thyrsus 5y ago
        Braking? Spend half the trip accelerating, the other half decelerating. The "erosion" problem mentioned nearby is still formidable.
- deleted 5y ago
  [deleted]
- ncmncm 5y ago
  That would be fine if you did not mind colliding with intergalactic medium at lightspeed for two million years. The term "erosion" seems inadequate.
- api 5y ago
  By close to light speed I meant maybe 50%. You are right if you get much closer, but there are some huge problems you get too… like having the cosmic microwave background blue shifted into gamma rays or the fact that a dust particle will annihilate you. I have wondered about the Alcubierre drive and similar concepts. Even if FTL is impossible due to causality protection principle issues, these may provide a theoretical way to travel at light speed (effectively) without the above issues. But we are talking very far future tech with outrageous energy requirements… if it is possible at all.
  - vl 5y ago
    > like having the cosmic microwave background blue shifted into gamma rays or the fact that a dust particle will annihilate you. But doesn’t this imply that there is preferred reference frame in the universe?
    - arrow7000 5y ago
      Not in terms of the laws of physics
    - Vetch 5y ago
      Kind of yes but also not really. The important thing is that the laws of physics are measured the same in all inertial reference frames. Consequently there is no non-contradictory sense in which an experiment could distinguish an absolute rest from other inertial motion. It's therefore not possible to talk about motion under constant velocity in an absolute sense, it must always be in relation to something else. Any other body could have been chosen as a (relative) rest frame but the CMB is uniquely convenient to coordinate measurements with due to its age and the extent which it permeates the universe. Physics is still the same in that frame as any other inertial frame.
  - bitcharmer 5y ago
    >like having the cosmic microwave background blue shifted into gamma rays This is patently false. It is indeed true that a relativistic spacecraft would see a highly anisotropic microwave background: a strong blueshift in the direction of travel, a strong redshift in the opposite direction. But at 99.5% of the speed of light, the blueshift factor is only about 20. This would shift the 2.7 K microwave background to a temperature of about 54 K; that is still pretty darn cold.
zikzak 5y ago
Research von Neuman probes
mr_toad 5y ago
> Intergalactic travel is many orders of magnitude harder than interstellar travel. Andromeda is about 25 galactic widths away. Our galaxies width is about 25,000 times the distance to Alpha Centauri. Alpha Centauri is about 266,000 AU from our Sun. Relatively speaking, the galaxies are quite closely bunched together, compared to their own mind-boggling sizes.
- hotpotamus 5y ago
  We don't even need to travel to it. We can just wait a few billion years for it to come to us.
  - mcswell 5y ago
    Wake me up when we get there.
  - roywiggins 5y ago
    Of course, that raises the question of why some civilization with a billion year head start isn't here yet.
- wruza 5y ago
  But AU probably isn’t a good way to compare this. Sun and the Solar System is 1,921.56 AU in diameter (google) So in these Solar System Units Alpha Centauri is only ~140 SSU away. Still more than 25, but comparable, and we are not in a dense neighborhood, afair: https://astronomy.com/magazine/ask-astro/2006/01/how-close-can-stars-get-to-each-other-in-galaxy-cores https://astronomy.com/magazine/ask-astro/2006/01/how-close-c... M15's center packs approximately 4 million stars per cubic parsec — that's more than 75 million times denser than the region around the Sun But some galaxies pack stars even tighter. M32, one of the Andromeda Galaxy's satellites, has the highest measured stellar density of any nearby galaxy — around 20 million stars per cubic parsec in its core! Not even HST can resolve M32's core into individual stars. A typical stellar separation at this density works out to 0.008 light-year, or 500 AU — about 12 times the Sun-Pluto distance — between stars. (500 AU being ~0.25 of our “SSU”, or 12 M32’s SSU)
plutonorm 5y ago
Natural or directed panspermia completely changes the nature of this discussion.If evolution occurs at the galactic scale then we can greatly raise the odds that we are among the first civilisations.

by api 5y ago

cft 5y ago

Even if a galaxy is 10 million light-years away, you can get to it in 1 month of proper (spaceship) time, if you travel fast enough. This is time dilation due to special relativity.

nefitty 5y ago
If this is true you just lit a candle in my internal temple of hope lol
- cft 5y ago
  In the Earth time, the spaceship would take a bit longer than 10m years to reach it, however. Plus the energy required to reach such velocity would probably be more than mass of the Earth if we were to annihilate it.
  - ant6n 5y ago
    Well, accelerating a 100 ton spaceship to 0.99c (assuming some sort of beamed propulsion) requires only 2000 Terawattyears [1]. Of course, to turn 1e6 years into 1 year relative time, one needs like 0.99999999c, one needs 2 million Terawatt years [2], which is a much bigger energy investment, but still not on the order of annihilating the planet. Breaking is gonna be a bitch tho. [1] 100000 kg * (0.99 * c)^2 / sqrt(1-.99^2) in Terawatt Years [2] 100000 kg * ( 0.99999999 * c)^2 / sqrt(1-0.99999999^2) in Terawatt Years
    - thyrsus 5y ago
      Braking? Spend half the trip accelerating, the other half decelerating. The "erosion" problem mentioned nearby is still formidable.
deleted 5y ago
[deleted]
ncmncm 5y ago
That would be fine if you did not mind colliding with intergalactic medium at lightspeed for two million years. The term "erosion" seems inadequate.
api 5y ago
By close to light speed I meant maybe 50%. You are right if you get much closer, but there are some huge problems you get too… like having the cosmic microwave background blue shifted into gamma rays or the fact that a dust particle will annihilate you. I have wondered about the Alcubierre drive and similar concepts. Even if FTL is impossible due to causality protection principle issues, these may provide a theoretical way to travel at light speed (effectively) without the above issues. But we are talking very far future tech with outrageous energy requirements… if it is possible at all.
- vl 5y ago
  > like having the cosmic microwave background blue shifted into gamma rays or the fact that a dust particle will annihilate you. But doesn’t this imply that there is preferred reference frame in the universe?
  - arrow7000 5y ago
    Not in terms of the laws of physics
  - Vetch 5y ago
    Kind of yes but also not really. The important thing is that the laws of physics are measured the same in all inertial reference frames. Consequently there is no non-contradictory sense in which an experiment could distinguish an absolute rest from other inertial motion. It's therefore not possible to talk about motion under constant velocity in an absolute sense, it must always be in relation to something else. Any other body could have been chosen as a (relative) rest frame but the CMB is uniquely convenient to coordinate measurements with due to its age and the extent which it permeates the universe. Physics is still the same in that frame as any other inertial frame.
- bitcharmer 5y ago
  >like having the cosmic microwave background blue shifted into gamma rays This is patently false. It is indeed true that a relativistic spacecraft would see a highly anisotropic microwave background: a strong blueshift in the direction of travel, a strong redshift in the opposite direction. But at 99.5% of the speed of light, the blueshift factor is only about 20. This would shift the 2.7 K microwave background to a temperature of about 54 K; that is still pretty darn cold.

zikzak 5y ago

Research von Neuman probes

mr_toad 5y ago

> Intergalactic travel is many orders of magnitude harder than interstellar travel. Andromeda is about 25 galactic widths away. Our galaxies width is about 25,000 times the distance to Alpha Centauri. Alpha Centauri is about 266,000 AU from our Sun. Relatively speaking, the galaxies are quite closely bunched together, compared to their own mind-boggling sizes.

hotpotamus 5y ago
We don't even need to travel to it. We can just wait a few billion years for it to come to us.
- mcswell 5y ago
  Wake me up when we get there.
- roywiggins 5y ago
  Of course, that raises the question of why some civilization with a billion year head start isn't here yet.
wruza 5y ago
But AU probably isn’t a good way to compare this. Sun and the Solar System is 1,921.56 AU in diameter (google) So in these Solar System Units Alpha Centauri is only ~140 SSU away. Still more than 25, but comparable, and we are not in a dense neighborhood, afair: https://astronomy.com/magazine/ask-astro/2006/01/how-close-can-stars-get-to-each-other-in-galaxy-cores https://astronomy.com/magazine/ask-astro/2006/01/how-close-c... M15's center packs approximately 4 million stars per cubic parsec — that's more than 75 million times denser than the region around the Sun But some galaxies pack stars even tighter. M32, one of the Andromeda Galaxy's satellites, has the highest measured stellar density of any nearby galaxy — around 20 million stars per cubic parsec in its core! Not even HST can resolve M32's core into individual stars. A typical stellar separation at this density works out to 0.008 light-year, or 500 AU — about 12 times the Sun-Pluto distance — between stars. (500 AU being ~0.25 of our “SSU”, or 12 M32’s SSU)

plutonorm 5y ago

Natural or directed panspermia completely changes the nature of this discussion.If evolution occurs at the galactic scale then we can greatly raise the odds that we are among the first civilisations.