[adflux]

I will start off by saying I have very little knowledge of physics or astronomy, but reading comments like these feels like I'm watching a 13th century British sailor confidently state what's on the other side of the Atlantic ocean...

Do we really know enough to be able to say if a planet is habitable? Or could there be other forms of life that we don't know of yet... We have only recently put a man on the moon, and now we're saying we would be able to detect dyson spheres...?

[wizzwizz4]

> We have only recently put a man on the moon, and now we're saying we would be able to detect dyson spheres...?

A moth doesn't even have electricity, but it can detect a lampshade. A Dyson sphere is basically a stellar lampshade; we can detect it if the laws of thermodynamics hold, and we're pretty sure they do. (A Dyson swarm is similar, though a bit harder to detect.)

[mcbits]

Maybe stars are the Dyson spheres, and their emissions are the waste energy that wasn't worth harvesting.

[wizzwizz4]

The spectral signature would be different if that happened. If all of the stars are Dyson spheres, then… maybe our models about stars are fundamentally wrong. But I doubt it; the maths to work out what the signature should be (given the composition) is pretty simple. Take a blackbody, put spectral lines as measured in the lab onto it, then redshift it.

[cletus]

People bring this up a lot. It's fair to ask. I do often find it comes from a place of wishful thinking. I mean I'd like to have FTL at my disposal true. But what we're dealing with now seem to be either hard physical limits or such close approximations to be effectively the same. The key two are:

1. The speed of light is a hard limit; and

2. Thermodynamics (particularly the Second Law) applies. Specifically, you can't get energy from nothing.

From this you can draw a few conclusions:

1. The likely sources of future energy are solar (most likely IMHO) and nuclear fusion. I hope fusion is viable. I'm not yet convinced it is. More exotic far-future options include antimatter and black holes. Antimatter is something you'd make. Think of it like a battery. So you still need the energy to make it. Black holes as propulsion are the same way. Generating power around a large black hole is theoretically possible but has a bunch of issues;

2. Reaction mass is a huge problem for traveling large distances, so much so that using photos to impart momentum seems the most practical. Fusion could be viable here. Antimatter and black hole propulsion are theoretically possible;

3. Because of energy demands, capturing the Sun's energy makes the most sense and doesn't require any "magical" or exotic science or technology;

4. Because of thermodynamics, eventually heat will radiate into space. It's really the only way of dissipating heat, ultimately.

5. Like I said, the IR signature is purely a function of temperature; and

6. A star with a Dyson Swarm will have a very strange (to us) spectrum. Very little visible light. High amounts of IR. There is really no hiding such a megastructure.

So this is essentially a natural conclusion based on physical laws we have no evidence for that they're false or meaningfully incomplete. Thing is, if the speed of light isn't a hard limit that actually makes it more likely we'd find spacefaring life not less because the reach of such a civilization would be so much farther.

[Loughla]

And it's also assuming that any life is like us, with no other technology or way to cycle/recycle heat other than to radiate it into space.

I mean, I know the proof of life is us, but the human-centered view of the universe does reek of prior historical "knowledge" that the earth was the center of the universe. I understand searching for life like us, as that is what we can extrapolate from current data. But to use that to infer that we're it, it's just too much for me.

[cletus]

This is the realm of the Fermi Paradox (which is a misnomer because it's not really a paradox at all).

The key question is that if planets are so common and space is so big, why does it seem to be so empty of life? You bring up an argument that maybe life is so different as to be undetectable. It's a fair question to ask but the beauty of the Fermi Paradox is that you don't need to argue about what's most likely. You simply have to be concerned with what's possible.

Let me put it this way. let's say that there is 1 other spacefaring civilization in the Milky Way and they've evolved like you said in a way completely alien to us and as such don't follow a path we can easily detect or at least we don't think to look for it. I can buy that as entirely possible.

But now let's assume there are 1,000 spacefaring civilizations in the Milky Way. What are the odds that every one them falls in this category? What are the odds that none of them follow a similar evolutionary path to us and what we consider highly likely? It becomes increasingly incredulous as you scale up the number of civilizations.

So what's more likely? 1,000 civilizations followed a path alien to us independently? Or that there are few to no other civilizations out there to detect?

To say we're the only 1 of 1,000 to follow this path is really a different kind of human-centric hubris.

Extracting energy from a star is so low-tech it defies logic to think we're the only ones who will (likely) do it.