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jordanb parent
Probably true, in that if you try to travel interstellar distances you'll going to have to deal with very hot particles hitting your ship on occasion. If you travel slowly the more time you're going to be spend getting hit by high energy particles. If you try to travel quickly you're going to have to deal with more relatively high energy particles. It's potentially enough to make interstellar travel impossible.
strictnein
Systems we built in the 1970s were able to easily pass through this though. Which doesn't seem to indicate that it would make interstellar travel impossible.
andrewflnr
Systems from the 1970s travel at, by interstellar standards, agonizingly slow speeds. The voyagers will be exposed to hard radiation for thousands of years before they get anywhere interesting. They will not survive.
strictnein
Not sure exactly why you're responding to me. The comment I was responding to was talking about the hot particles that would be encountered, and that their existence could preclude future interstellar missions.

What level of "hard radiation" are they now getting bombarded by that we will be unable to shield systems from in far future interstellar space travel?

andrewflnr
I'm saying the Voyager probes don't make a counter example to interstellar travel being impossible. That's still very much an open question. We might be able to develop adequate shielding to protect spacecraft from radiation over mildly geologic timespans, but we might not. I'm certain it won't be as easy as you seem to think it is.

(Unless you count slinging a dead pile of former computers through a distant star system as successful interstellar travel, but that's not what most people are interested in.)

mxkopy
Imagine if a dead pile of computers that wasn’t ours arrived in our solar system, I’d call that successful by some metric
SoftTalker
It's impossible for many reasons unless there are physics we haven't discovered yet. To me that's the simple answer for the Fermi paradox.
andrewflnr
The Fermi paradox doesn't require travel, though. The lack of any sign of life at all is still surprising (no radio signals, etc), even if we knew it couldn't physically come here.
flatline
It would take a lot of power to send even a radio signal that could be picked out from the noise at a few light years. Add a requirement for that signal to be more or less continuous over geologic timescales - we’ve only been able to emit and detect these for ~100 years - and my personal surprise diminishes rapidly. Huge distances in time and space with human-level technology make detection highly unlikely.
ojosilva
Yes, and I would add my favorite hypothesis to the paradox, an anthropocentric assumption theory of self importance... or let's call it an anthropocentric bias:

Humans tend to define intelligence, life, and communication based on our own structure -carbon-based biology, electromagnetic signaling, language, symbolic thought, etc. This narrows the scope of our search.

We assume other civilizations want to communicate, would use similar media (radio, light, mathematics), and would send signals we could interpret. This ignores other potential modalities (quantum, neutrino, gravitational, exotic matter, etc.) or entirely non-signal-based forms of interaction.

We may not even recognize signs of intelligent activity if they don't resemble our expectations, ie entire civilizations could exist in forms of computation or energy we can’t perceive.

We assume ET intelligences are aligned with our timeframe or curiosity. Maybe they don’t care to communicate, see us as trivial, or operate on million-year attention spans.

It may reflect less the silence of the cosmos and more the limits of our understanding, especially the assumption that we're capable of detecting or interpreting intelligence beyond Earth. A epistemic humility, or rather our lack of it.

dgfl
Nobody would be communicating with neutrinos or gravitational energy. EM radiation is way easier to emit and detect, and at cosmic distances they all scale exactly identically (inverse square law). The other things you mentioned are mostly sci-fi inventions and there’s nothing in known or unknown physics that would hint towards them being plausible communication media.

It’s not about being shortsighted, it’s about everyone being constrained by the same laws of physics. Our models, however imperfect, are still unreasonably good.

esprehn
The counter argument is that even if civilizations exist with all the properties you described, given the vastness of space, there should be another civilization that pattern matches to us.
ojosilva
Sure! All the hypothesis in the Fermi paradox deal ultimately with calibrating our expectations of making contact, not with denying the existence of "STEM-enabled" species like us yearning for an alien encounter.
andrewflnr
There's epistemic humility, then there's indulging in unfalsifiable fantasies in the name of not ruling anything out.

> Humans tend to define intelligence, life, and communication based on our own structure -carbon-based biology, electromagnetic signaling, language, symbolic thought, etc.

I would posit that none of these properties are coincidences, and are in fact likely to evolve convergently in most if not all circumstances hospitable to life. In particular I very much expect ET life to be carbon based; I don't believe there's a true viable alternative outside scifi (hint: silicon ain't it).

> entire civilizations could exist in forms of computation or energy we can’t perceive.

Could they? Really? There aren't that many gaps in the Standard Model. The aliens could be made of dark matter, I guess, and remain forever undetectable, but that's not to far off believing in invisible fairy kingdoms. And it still wouldn't explain why the baryonic sector is so devoid of detectable life. Ethereal undetectable aliens don't mean regular ones can't also exist.

> Maybe they don’t care to communicate, see us as trivial, or operate on million-year attention spans.

This one I'll grant (sort of: what's the evolutionary path toward such entities arising?), but it's still weird that we haven't seen any sign at all of them. These entities live on million-year timescales but have no visible effect on their surroundings? Why?

And more importantly, why is that the only thing that happens? Because if it isn't the only thing, then the question remains of why can't we see anything else?

andrewflnr
Radio signals aren't the only sign. I'd really love to see some sign of megastructure engineering, but even detecting O2 in an extraterrestrial atmosphere would be huge.
IAmBroom
Those would likely be extremely low albedo objects, so harder to detect than radio signals by many orders of magnitude.

A Dyson sphere would be virtually invisible, except for a hard to reconcile "blackbody-profile versus apparent size" ratio.

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