In a billion years you can get across the Milky Way traveling at only 0.1% of the speed of light. We could detect self replicating VN machines, if they were here dissecting the Earth - but they’re not.
Great.
Such a ship would still be undetectable with our technology unless it passed extremely close to Earth. What’s the chances of that?
I think we’re talking about two different things. We can’t observe the VNMs unless it’s close to the Earth - but the effects of the VNMs (and the effects of other things) can be observed from much farther away. We’ve observed an exoplanet 13,000 light years away - so 13,000 years ago, there were no Von Neumann machines taking that planet apart.
Some megastructures are also detectable from very far away.
I think it’s unlikely that any civilization will ever be able to build anything remotely detectable from lightyears away. First of all, most of those structures are pretty pointless, and secondly, no matter how advanced the technology gets, there’s a limit to the available energy in a star system. But, that doesn’t mean there aren’t other civilizations in the galaxy - it just means we will never spot them.
It’s certainly possible that there are civilizations we’ll never see. But spectrography of exoplanets might detect CFCs or some other obviously artificial chemical of a civilization that has no interest in megastructures or space travel. We’ve already analyzed the chemical composition of an exoplanet atmosphere 65 light years away (HD 189733b) - and we’re not that advanced.
I said megastructures, beacons and self replicating probes.
The first two are broad terms so there is no intrinsic distance at which they cannot be detected. There is no reason to say 50 light years or indeed any number of light years.
The latter is a technology that could visit every star system in a tiny percentage of the age of the galaxy.
I would love to live in a galaxy teeming with advanced life. We already have reason to doubt that that’s the case though.
If you want to talk science fiction, then, sure - postulate an alien civilization with limitless resources, able to build structures detectable at multi-lightyear distances. Or, design probes than can replicate themselves out of the infinitesimal materials in interstellar space.
But, I was responding to the ridiculous assertion that since we haven’t detected any evidence of other civilizations, we must be the only one. That’s just assuming facts not in evidence to me…
…which we necessarily are, in this context.
I mean, when you were talking about “millions of advanced civilizations”, what did you mean? Millions of civilizations that have not exceeded human technology circa 2023?
That’s three straw men in quick succession.
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No-one is claiming limitless resources; just sufficient resources to build megastructures, powerful beacons and so on, and we already know that such energy does indeed exist.
For example, where would a species get the energy from to build a Dyson swarm? Well, from a Dyson swarm. Which is to say: they put one collecting device in place, that’s already gathering stupendous amounts of enery compared to humans’ current energy budget, a small fraction of that energy is then utilitized to transport the next device into place, and so on. -
No-one has said probes that replicate themselves from “infinitesimal materials”; the typical concept is that they are able to mine asteroids.
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Finally no-one has said we “must be” the only one. @Dallas_Jones (and Prof Brian Cox) has said that we are likely to be the only advanced species in our galaxy, based on the lack of any detectable phenomena, and I think their reasoning is sound. That’s not the same thing as claiming to know.
Evidence and facts are the basis of science. We currently have no evidence to show another intelligent species in our galaxy, at all. So right now it is the fact that we are alone. Fuzzy pictures of what are probably camera artifacts are not evidence.
We have zip, nada, zero, facts to support the existance of any other intelligent, technological, society anywhere. These are the facts. Probabilities are not facts. There MUST BE is not a fact.
We are the only ones, that is the current scientific fact.
Would it not be more correct to say that we have no evidence of any intelligent life outside of Earth? (Possibly no evidence of any life outside Earth?)
Nonsense.
“We think we are the only ones” might be more accurate. But, to make a definitive statement that we are alone in the galaxy is absurd. Even to saying that it’s “evidence” is questionable. It’s like being the only person in a room and saying that proves that you are the only person in the galaxy.
And, not being able to detect megastructures is much more likely to be evidence that they are impossible, not that there is nobody to build them.
@Dallas_Jones is correct that we currently have absolutely zero evidence of alien life or intelligence. I hope that changes in my lifetime, but for now we are at zero.
Many of the Fermi paradox arguments, probably contrary to what is being argued, for me work to adjust the prior probability of there being aliens. If mega-structures, galaxy spanning civilizations, replicating probes, and other things that people argue should make aliens easy to find are still not detectable, then that lowers the probability aliens exist.
I can state with a great deal of confidence there is no dog in the room. I do not detect an ant in the room, but my conclusion that no ant exists in the room is not well supported. As the supposed detectability of aliens moves on the ant-dog spectrum, our confidence that not finding aliens means they don’t exist is going to change.
I am alone in the room, but I can detect evidence of people all around me. Structures, sonic signals, phenomenon best explained as being caused by an intelligent agent, all lead me to believe I am not the only person in the galaxy.
I’d think that’s an odd way of putting it.
As far as we know right now, we are alone. Even people who believe our galaxy is likely teeming with advanced life generally agree that we don’t know of any other ETIs yet (a few might think ETIs have visited earth, but they are the minority (certainly worldwide if not the US)).
So if the fact that you are alluding to is that as far as we know we’re alone, well duh.
OTOH if the fact that you’re alluding to is that we actually are alone, well, we don’t know that. That isn’t a fact.
All we can say is that the lack of any detectable phenomena gives us reason to doubt the existence of advanced ETIs.
Sorry, jumping into the middle of this conversation, I don’t find those compelling either though some are a bit odd.
What about the navy pilots stating they’ve visually identified strange aerial objects, I believe a description of a black sphere inside a cube or vice versa has been mentioned in several different reports.
It’s all very strange.
Now Oumuamua, again almost certainly entirely natural but there were some unusual aspects to that encounter.
It is probably the same report repeated by several different people. Pilots are not very good at reporting the details of small stationary objects which they zip past at hundreds of miles per hour. Here’s a picture taken by a pilot on their own smartphone as they zipped by one such object; the pilot described this as a ‘flying shield’.
It was almost certainly a ‘Batman balloon’ released by a child from a seaside resort on the East Coast.
Interesting, thank you!
Until any evidence to the contrary is found, it isn’t unreasonable to assume that we are alone. When the evidence changes, my mind may change.
That’s just “Human Exceptionalism” of the worst kind.
No-That is reality. You deal with the evidence you have, then deal with new evidence as it comes in.
It really doesn’t matter very much. I think it’s unlikely that we are very special, but I also think it’s unlikely we will ever find out otherwise. The Universe is too big and too sparse.
So, believe what you want.