“Either extraterrestrial civilizations (ETCs) are incredibly rare (or non-existent), or they are deliberately avoiding contact with us (aka. the “Zoo Hypothesis“).”
There is a 3rd possibility - it may not be deliberate.
Our position in the Milky Way is really out on the ass-end of it. We are nowhere near galactic central. If our current understanding of slower than light travel is correct, it just may not be possible for other civilizations to reach us.
When it comes to communications, and our radio sweeps of the galaxy turning up nothing, well, we’re assuming any advanced civilization is still using radio transmissions.
Look at our recent experiment with laser based communication:
100 or so years after radio communication was widespread, we have the technology to eliminate it. There may be other methods orders of magnitude beyond that. We could be awash in alien communication streams we just can’t percieve because ours are too primitive.
There are also hundreds of other theories that can potentially explain it. Like, 100 years really isn’t a long time on cosmic scales. Maybe we’re late to the party and intelligent life wiped itself out already. Maybe we’re early, and we will wipe ourselves out before a new intelligence even figures out where the copy paper is.
We don’t want to be near the galactic center, there’s too much radiation. A quiet spot out on one of the arms away from supernovae and active objects is a much better place for life to evolve.
At this point our own radio is even too advanced for an alien civilization to detect. An interesting thing about radio is that aside from a few lingering powerful analog signals (AM/FM radio, active radar) our modern spread-spectrum radio is hard to distinguish from background noise. It’s an interesting consequence of information theory, as bandwidth and noise tolerance grow, if you aren’t looking for a signal it becomes almost invisible. We also do a lot with very little power now due to these amazing encoding methods, when I was a kid and the analog cell phone was novel we would have outright said that a phone could never communicate directly with satellites. Not enough power or antenna in your pocket. Yet here we are.
So any civilization that develops radio is only likely to send out a short burst of detectable radio before disappearing within 100 years, even without switching to an alternate technology. This makes radio an almost impossible thing to search for in a vast galaxy where time can separate us even more than space.
given the age of the Universe and the relatively short time it would take for an advanced civilization to spread across the Milky Way Galaxy (650,000 years, by Hart’s estimate), Earth should have been visited by an extraterrestrial civilization (ETC) by now.
It took humans 30,000 years to cross the Atlantic. Using modem propolsion systems, it takes us two years to get to Mars and 40 to reach the edge of the solar system. This seems like an extremely generous estimate considering the Milky Way has a 50,000 light year radius.
I’m as bullish about extraterrestrial life as anyone, and I think a fuller survey of even just the current Solar System has potential. But I have no idea how you get a full galactic survey in so short a time, given what we know about the soft limits on speed of travel and communication.
By Tipler’s refined estimate, an ETC would be able to explore the entire galaxy in “less than 300 million years.”
That definitely feels like it’s more in the ballpark. But, again, it presumes a certain amount of steady cartography by the hypothetical fleet of Von Neuman probes.
There’s a Sci-fi series called The Bobverse that explores the idea of a sentiment fleet of Von Neumans exploring the galaxy, and the various trial and tribulations involved. One point it discusses is that even with a saturation of probes, you don’t get real time communication. So even in a hypothetical universe where alien life did exist and survey earth, what are they odds they’d be watching us at the moment of our development. What would an alien AI be looking for and what would it do when it was discovered?
We could still be too primitive to bare noticing. Or we could be living in between blinks of an alien camera that only reports back every 1000 years.
As we look out at the cosmos, we could be looking at things we don’t understand. After all, what does a star surrounded by a Dyson Sphere look like to a telescope that is searching for glimmers of light, heat, and gravity? SETI is operating purely on conjecture. That’s assuming alien civilizations are even capable of creating these hypothetical superstructures. Or that the structures would function as we intuit.
At some level, I have to question if we know what we’re looking for. Because so much of this feels like we’re searching for humans deep in space. Perhaps the reason we can’t find aliens is that they are simply… too alien.
No, rare intelligence and to a lesser extent rare earth remain as convincing as ever. Potentially habitable does not mean life sustaining, and given the lack of strong biosignatures on any of the examined near earth exoplanets, I’d say that there is indeed increasing evidence that life of any kind really is that rare, much less intelligence.
It is just absurdly hard to get conditions right for microbes to form on a reasonable timeframe is a solution after all.
All this time? What like less than 100 years looking only? That’s a blip on the cosmic scale. 100 lightyear sphere of our galaxy is what, less than 1%? With all the theories and possibilities of what’s going on out there, it’s way too rash to start theorizing like this in my opinion.
I haven’t seen the evidence of ‘water oceans’ out there that are about more than a few water ‘geysers’ spewing from below the frozen surfaces like our breaths on winter mornings.
Whenever I hear the words ‘water’ or ‘life’ in a message from NASA I think, ‘Hmmm… who stands to gain from this PR?’ (At least telescopes return great pix and -other, visible- evidence.)
In case anyone wasn't aware, nearly all space photos that you've ever seen have had their colours tweaked. It's standard practice in space photography. Nebulae and galaxies and planets aren't as colourful as they appear in photos. They do it either to make the features more obvious for study, or just to make them pop more to drum up interest in space exploration. Nothing wrong with it, just be aware that what you see isn't reality but an interpretation.
Really though, I don’t know why it never crossed my mind that the picture of Neptune was so… saturated. It’ll take a little bit to reconcile this new perspective of a “light bluish-green” Neptune. It’s just so jarring to alter a belief held since my childhood.
The latter, I suspect. That’s certainly how forming a neutron star works in the first place, because if a star gets so dense that it can form neutronium then the neutronium (which is far more dense than the core was before) can easily keep making more.
It’s a similar story with black holes. Get past the threshold at which it forms, and the process runs away and swallows the whole star.
If a quark soup is more dense than neutronium, then it would be fairly all-or-nothing
I used to think this idea was kinda silly and based on flimsy and handwavey justification, but then I saw a colloquium by a famous black hole physicist on it. Now I REALLY think this idea is silly and made up!
Oh! They don’t mean that black holes must come in perfect pairs! The headline makes it sound like it’s about wormholes across vast distances. No! What they’ve found is a stable “orbit” solution for the two-body problem. Normally when you place two bodies anywhere in an empty universe, they will gravitate towards each other until they collide. But in a universe with dark energy, there is some perfect distance between them, where the accelerating expansion perfectly counterbalances the accelerating attraction. They’ve used general relativity math to actually calculate such an arrangement.
The “stable” orbit in this case is the same kind of stable as a pencil balanced on its sharp tip - if it tilts even slightly one way it will fall out of control. Although they tantalize the idea that they might be able to make it truly stable against small perturbations once they finish their spinning black hole solution.
I would like to have known some specific numbers examples! Like if you have as much dark energy as our universe, and two 10-solar-masses stellar black holes, how far apart would that be? Is it like 1Ly or 1MLy? How far for two 10-million-solar masses supermassive black holes? The formulas they created should give the exact answer but I am not skilled enough to substitute the correct numbers for the letters.
astronomy
Aktywne
Magazyn ze zdalnego serwera może być niekompletny. Zobacz więcej na oryginalnej instancji.