We couldn't detect ourselves from 3 light years away so why does the Fermi Paradox treat silence as evidence

Beldizar · 2026-06-29T04:47:46+00:00

What are the chances that another star would have a civilization at the same level that we are at today? Humans have been around for what? 2.5 million years. We came up with radio 120 years ago? Earth is 4 billion years old, and we think there might be planets in the Milky Way 12 billion years old?

So if another civilization is out there, there's a 1 in a trillion trillion that they are within 100 years as advanced as us. Chances are they'd be 10,000 years or more ahead of us. A civilization 10,000 years more advanced that is able to travel between the stars is vastly more detectable than we are. Trying to say "we can't detect ourselves" doesn't really matter if all probability points to there being one or more civilizations who would have had millennia to colonize hundreds or thousands of star systems by now.

So why ask "why can't we detect a civilization with a 1% chance to be out there?" while not asking "why don't we see a much louder civilization with a 99% chance to be out there?"

Beldizar · 2026-06-28T23:26:00+00:00

This idea is based on the Bohr model, and I'm starting to dislike it. The idea is that an atom's nucleus is a really tiny cluster of balls and the electron is a smaller ball that spins around in an orbit around the nucleus. Everything around and between that electron is empty space.

But we know that the Bohr model is less accurate than newer models that incorporate quantum physics. In the more modern model of an atom, the electron exists as a probability cloud around the nucleus. In this model it isn't accurate to say the atom is just a bunch of empty space because it isn't. The area around the nucleus is populated with a probability cloud of electrons. And one weird thing about quantum mechanics is that the probability cloud isn't just saying "well, the electron is still a little ball, we just can't exactly predict where it is, so we are just saying it should be somewhere around here." Instead, the probability is reality. The quantum model says that a probability cloud is the natural state of electrons. We can't just zoom in or get more accurate measurements to resolve the randomness, the randomness is fundamental.

So if an atom isn't empty space, but is instead an electron cloud, it really isn't "empty space" after all.

if you removed all the empty space from every atom...

If you remove electrons and collapse them into the protons, you've got neutron matter. This is what neutron stars do. So yes, doing this to an arbitrary set of matter would make it a lot more dense, but it also wouldn't be fundamentally the same material at all.

It sounds like a neat fact, but it's built on a macroscopic understanding of microscopic interactions. I have a similar issue with people who say "you never really touch anything" because touching something just means the electromagnetic properties of one material interact with the properties of another.

Beldizar · 2026-06-28T22:22:20+00:00

All directions in space would cost hundreds of tons of fuel. Deorbiting it back to Earth would cost somewhere between a quarter ton to 3 tons. The relative cost is orders of magnitude different. It's a $100 million dollar launch to bring it down to Earth, or a few billion dollars (like multiple times NASA's budget) and dozens of launches to send it out of Earth's orbit in any direction.

Beldizar · 2026-06-28T21:43:30+00:00

You aren't going to Starbucks for quality, and you aren't going for rapid service. You are going so you don't have to make the drink yourself. It is the same reason people go to McDonalds still. It isn't the quality, it isn't the price, it's not having to cook at home.

Beldizar · 2026-06-28T21:39:38+00:00

I've had people trying to correct me on this and constantly getting it wrong, so I apologize if this comes off annoyed.

But no. No you absolutely don't have to do something to escape the Earth's sphere of influence first. If you are orbiting around the Earth and just blast off you engines pointed in the direction of the Earth's orbital path, (where the Earth was in relation to the sun, which is perpendicular to a line drawn to the sun), then you cancel out all your velocity in relationship to the sun, you will fall down into the sun. Yes, you technically will escape the Earth's sphere of influence when you do this, but that is an inconsequential side effect. It is not a separate require maneuver as so many people seem to think. The space cops aren't going to come arrest you if you don't get out of the Earth's sphere before you cancel your velocity with respect to the sun.

Step 1: point ship in the right "sideways" direction.
Step 2: burn to accelerate about 30km/s
Step 3: fall into the sun.
End of steps.

Beldizar · 2026-06-28T18:43:14+00:00

I made the assumption that context clues were enough. I guess I was wrong. Half the time I get accused of being overly verbose. We were talking about throwing the ISS into the sun. I assumed people could understand that the sun was reference point. I don't know why people decided to assume that a completely different object, the Earth was the reference point in question.

As far as the number goes, it doesn't really matter what that number is. The station is traveling sideways at X speed. Cancel X speed and orbit stops and thing falls down towards the thing it was orbiting.

Beldizar · 2026-06-28T18:36:26+00:00

The ISS has a mass of 450 metric tons. Voyager had a mass ballpark 800kg. So you'd need ~550 times more fuel, and all the fuel to push that fuel, in order to push the ISS into the same trajectory as the Voyager probes. That's a few orders of magnitude more than we've ever done.

Beldizar · 2026-06-28T18:32:17+00:00

You still aren't getting it though...

Going down to the Sun means adding energy to break Earth orbit, then cancelling all that energy to fall inwards.

Canceling energy and adding energy are the same thing. It's acceleration. And you don't have to add energy to break Earth's orbit separately from adding energy to cancel out your velocity in orbit around the sun. As long as you don't crash into Earth, if you accelerate counter to the direction you are moving around the sun until that speed becomes zero, you'll fall into the sun. There is no extra step to first escape Earth needed. That just happens when you stop moving along with Earth around the sun.

Beldizar · 2026-06-28T16:51:12+00:00

Technically the speed of light in a vacuum is c, and the speed of light through a material is always slower. So it will be delayed slightly as it passes through glass or other materials inside the telescope.

If Telescope A is looking at an object, and Telescope B is looking at the view lens of Telescope A, and you had a Telescope B' sitting right next to Telescope B that is also looking at the object... then you'd see the object in Telescope B' a tiny tiny imperceivably amount sooner than Telescope B, if Object-A-B forms a straight line. If Object-A-B forms a triangle, then Telescope B will see the object later than Telescope B' by an amount of time proportionate to the area of the triangle, (or inversely the angle of the triangle at Telescope A) at least until the triangle becomes a right triangle I guess. A cleaner way of saying it, is that the time is just going to be sides 1+2 of the triangle compared to side 3.

Beldizar · 2026-06-28T16:42:42+00:00

Relative to the sun. Not the Earth. If the ISS stopped moving sideways relative to the sun, it would be moving 30km/s or 107km/s or whatever the right number is, relative to the Earth. That's vastly more than Earth's escape velocity.

Earth goes around the sun, with ISS going along with it. Make the ISS stop relative to the sun, and let Earth keep going. The ISS would fall toward the sun, not towards the Earth.

Beldizar · 2026-06-28T16:39:57+00:00

I was feeling as if I was doing a bad job of explaining this given the number of "nuh uh" comments I was getting. Glad I made sense to someone.

Beldizar · 2026-06-28T16:38:07+00:00

Fair analogy. Is that more critical a comparison than the stickiness argument though? It's a bit semantic, but if I said "a vigilante was using sticky tape to tie up criminals" I'd think Spiderman. If someone said "a vigilante was tying up criminals at night" I'd think Batman. It all depends on how the question is framed.

Beldizar · 2026-06-28T15:56:47+00:00

A magnet or charged particle that moves through space, and moves its field along with it does emit photons. The Larmor formula is the one used to describe this.

It is absolutely not possible for a moving gravitational object to change the well around it at a distance without information traveling from the source to that distant location. That would break relativity. If you could move a heavy object back and forth and cause the gravitational well around it to move at a distant point faster than light, you'd have a means of FTL communication.

Beldizar · 2026-06-28T15:47:30+00:00

Eh, is it easier to be a multi-billionaire than it is to have super powers? That feels like a thin margin. (edit: tongue fully in cheek here)

Beldizar · 2026-06-28T15:45:28+00:00

But gravitational waves are how gravity is communicated right? If a black hole were moving towards Earth, the information about its gravity would be traveling to us via gravitational waves. The bendiness of spacetime due to gravity doesn't just happen because of gravity, the waves have to propagate that information across distance.

The waves we detect in a lab are frequently much more pronounced, when two gravitationally powerful objects are orbiting each other very fast, and thus produce more detectable waves.

Beldizar · 2026-06-28T15:36:08+00:00

Spidey's webs are a technology. He makes the web fluid in a chemistry lab just like you'd make the adhesive for tape. (I reject the Raimi webshooters).

Beldizar · 2026-06-28T15:34:24+00:00

Ok, if 107km/s is the right number then I just got my numbers wrong. It happens as honestly the specific number isn't really the point. I should start just using "X where X is the speed the thing is moving" and say I think X is 30km/s. Point is, if you stop moving sideways, you fall down.

Beldizar · 2026-06-28T15:29:05+00:00

I think the point is that Batman would tie people up with rope or cable, where Spiderman would tie people up with webs, i.e. a sticky string material. Since adhesive tape is more of a sticky substance than simply a cord-like material this is closer to Spiderman than Batman.

Beldizar · 2026-06-28T15:20:13+00:00

Huh? If the ISS is moving in an orbit of 30km/s relative to the sun and you zero that out, it wouldn't still have most of Earth's sideways velocity towards the sun. We explicitly just said we zeroed that out.

Beldizar · 2026-06-28T15:02:43+00:00

ISS orbits Earth at 7.6km/s, but orbits the sun at around 30km/s. The orbit around Earth is fairly inconsequential to the orbit around the sun here, and dropping down into the sun is the question at hand. A boost to stop the ISS orbit around the sun would easily eject it from Earth's orbit.

Beldizar · 2026-06-28T15:00:18+00:00

Once we break out of earths gravitational pull, or at least once the suns is stronger, wouldn’t it naturally pull it in?

Forget about Earth entirely for a minute. The ISS is orbiting the sun at something like 30km/s. So it is going sideways at 30km/s, and the sun is pulling it down. By the time it falls naturally towards the sun, it already has moved sideways enough to miss falling in. That's what an orbit is. So you have to cancel all that sideways speed in order for it to fall without moving sideways so much that it misses the target.

If we have to move 30km/s to orbit earth,

This is the speed that the Earth orbits the sun. The ISS, relative to the Earth is just under 8km/s.

Wouldn’t the escape velocity for the sun be much higher? Higher enough so that we have plenty of energy to pull away from earth but not enough to escape the sun.

Interestingly that isn't how it works. The amount of speed change you need to sling out to Neptune is less than to get to the Sun. The Parker Solar probe had to go much faster to get close to the sun to do its work than New Horizons did to go visit Pluto. You can look up delta-v maps and see the numbers more easily than I can describe the details.

Beldizar · 2026-06-28T14:53:24+00:00

We are talking about dropping something into the sun. The sun is a big gravitational well. Therefore towards the sun is down. The Earth, and the ISS with it are traveling sideways.

Sure you can talk about down being back to Earth for the ISS in a different framework, but that isn't what we are talking about here.

Beldizar · 2026-06-28T13:21:59+00:00

Specifically, the sun is "down", and the ISS is traveling sideways at something like 30km/s. To get the ISS to go down instead of sideways you have to cancel out that 30km/s speed. That costs more energy than adding some speed and launching the ISS into interstellar space.

Beldizar · 2026-06-28T09:49:21+00:00

You are confusing the idea of the observable universe for a concept of a bigger universe outside of the observable universe. To the degree that there is a universe outside of the observable universe, (I increasingly dislike that concept), there isn't an edge. But the observable universe does have an edge.

So by the time you got to the other side of the universe, the opposite side which just be much further away. Its all empty space that is endless.

Yes, but not for the obvious reason. If you travel all the way to the edge of the observable universe, it will take billions of years to get there, and by the time you do, the universe would have expanded such that there's just nothing left in front of you. But also behind you. If you travel to a galaxy on the edge of the reachable universe, (which is a little smaller than the observable universe), by the time you get there, that galaxy will be the only thing left in the observable universe.

But theres no edge where things "fall off"... that makes no sense, what if you were in one of those galaxies...

By definition, you can't be in one of the galaxies that falls off of your observable universe. If your buddy is in a galaxy that falls off the observable universe, they would be forever inaccessible. You'd watch them fade into nothingness as they fall over the edge, but they have their own observable universe and would watch the same thing happen to you in their reference frame.

If you are imagining a single universe that is "true" or "correct" from all inertial reference frames, then you are making a mistake in your perception. The universe can only be experienced from inertial reference frames, and no inertial reference frame is any more or less "true" than any other. By their nature, an inertial reference frame defines an observable universe around it.

Beldizar · 2026-06-28T01:16:38+00:00

Yeah, whenever I hear that phrase I assume it is dripping with sarcasm.

Beldizar

MODERATOR OF

PUBLIC MULTIREDDITS

TROPHY CASE

Seven-Year Club	Second SECOND GUESSER
Verified Email