Thread by @davidfickling

Here's a thread about how LED lightbulbs, underexposed photos and colonialism suggest an explanation for the Fermi paradox -- the mystery of why there's no sign of intelligent life elsewhere in the universe:

Enrico Fermi was one of the most brilliant physicists of the 20th century -- the first to realize the power that could be unleashed by splitting atoms, and (with Edward Teller, on the left) a key architect of the nuclear bomb.

He was working on developing the hydrogen bomb with a group of fellow scientists in 1950 at Los Alamos, New Mexico, when he had a lightbulb moment:

Where are all the aliens?

This was the era of UFO panic (The Day The Earth Stood Still came out in 1951).

As a scientist Fermi was, I think, dismissive of all the news reports about little green men.

But as a statistician he had a contrarian idea: Even if you assign very low odds to stars producing planets; planets producing life; and life developing into technological civilizations -- if the number of stars is large enough, there should still be countless civilizations.

At least some of these civilizations should clearly be visible to us. Look at the energy signature given off by human radar activity, or street lighting, or by the atom bomb itself!

Then imagine *how much more* energy a more advanced civilization would be using, and radiating.

So why can't we see them?

The main explanations I've seen tend to be a bit grandiose:

Perhaps intelligent life really is incredibly rare? Perhaps we're alone?

Perhaps civilizations destroy themselves too quickly to send out a lasting signal?

Perhaps there's a galactic federation out there but they're keeping us isolated until we're more developed, like animals in a national park. (This is more or less the plot of The Day The Earth Stood Still).

Here's a simpler theory: Seeing extraterrestrial civilizations is just really, really difficult, unless they go to an extraordinary amount of effort to be seen.

Have a look at this photo. What stands out? The Sun, right?

The energy given off by human civilization is a torch bulb next to the Sun's Klieg light.

The Sun puts out 3.486 × 10²⁶ watts of energy.

All the electricity generators on Earth have a capacity of about 7.5 x 10⁹ watts.

ag.tennessee.edu/solar/Pages/Wh…

If we dedicated all of global electricity generation to shining lights into space, the Sun would still be about a billion *billion* times brighter.

It's like an underexposed photo -- you can't see the foreground detail because of the intensity of the background light.

And of course, we don't dedicate all electricity to shining lights into space. Most isn't producing light at all.

In fact, even now the trend is towards more thrifty, rather than more profligate use of energy.

LED bulbs use just 20% of the energy of incandescent ones!

Fermi was oddly ill-placed to have a good perspective on this because he lived through an era when human energy demand looked exponential.

When he was born, electrical grids were in their infancy (one of the first was built near his home in Rome 19 years before his birth).

By the time he came up with the Fermi paradox he'd unleashed the power of the atom.

Many saw nuclear bombs as a potentially mundane way to produce energy for building harbours or powering spaceships.

It was also the era of exponential growth in radar and television.

Signals at that end of the spectrum stand a far better chance of getting picked up by extraterrestrial observers, because there's less background noise in the universe at those frequencies.

The most prospective range for picking up ET energy signals, in fact, is round about where radar and TV signals cross over -- wavelengths of between 18cm and 21cm, the so-called "water hole" where background noise from interstellar space is unusually quiet.

Here's the problem, though. Less than a century after the dawn of radar and TV broadcasting, the world's radio signature is already fading: radioworld.com/industry/the-e…

People used to speculate that aliens would be watching TV broadcasts of I Love Lucy, but even humans are increasingly not doing this.

If we watch I Love Lucy, it's on cable-delivered streaming services which don't leak radio signals.

We're still using plenty of radio-band traffic, but it's increasingly low-powered, short-range signals between mobile phones and towers rather than the sort of high-powered, long-range signals common in the broadcast TV era. That's much less likely to leak into space.

If extraterrestrials were to get a hint that there's life on Earth, the most likely thing they'd spot is not humans but pond scum.

Blue-green algae are the reason that 21% of our atmosphere is oxygen, which is highly reactive and so rare in the universe in its elemental form.

If an ET was watching the Earth crossing the disc of the Sun (the way we identify planets outside the solar system), the atmosphere's oxygen content would show up under spectroscopic imaging far more clearly than humanity's electromagnetic signals would.

There's also a problem around "focus" -- how narrow the energy beam is.

If it's wide, the energy signal will be widespread but indistinguishable from noise to most receivers.

If it's narrow, the signal will be more distinctive but more likely to miss the receiver altogether.

All our radio-spectrum leakage is almost by definition "wide" -- the bits that escape into deep space are the bits that aren't going where they're meant to go.

Various papers by SETI researchers over the years have found vanishingly small odds for the Earth blundering into the path of electromagnetic communications between ET civilizations:

cambridge.org/core/journals/…

arxiv.org/abs/1410.7796

OK, so the odds of *accidentally* revealing ourselves to extraterrestrials are extremely low. But how about *deliberate* signals?

If you point a really strong radio beam in just the right direction, surely that's detectable?

Well, yes. But consider the problems.

[breakfast break]

OK, back. It's worth considering how precise "just the right direction" is.

Take the Arecibo Message -- a broadcast from Puerto Rico's huge Arecibo Observatory in 1974.

Imagine for the sake of argument that it was directed at a technological civilization, with just the right radio receivers, reaching their solar system at just the time they were looking for transmissions from space. Good odds for getting the message, right?

Well, no! The Arecibo Message took just three minutes to transmit, so if the alien observatory was facing the wrong way during those three minutes due to planetary rotation, the radio signal would have landed on their planet undetected.

The @SETIInstitute uses a telescope array to create a huge "virtual telescope" to increase the odds of catching a transmission, but it's still dependent on being faced the right way at the right time!

There's a trade-off around power, too. If you want to be really visible you'll have a message that's "always on".

But while you can transmit a powerful signal for a short time quite easily, the energy consumption of a long-lasting "beacon" quickly becomes, er, astronomical.

That doesn't mean it would never happen. But it does mean that a civilization sending out such a message would have to be really, really dedicated to making contact. And that's where colonialism comes in.

Here's a sort of SETI account from 1642 -- Dutch mariner Abel Tasman's account of his landfall on the coast of Tasmania not far from modern Hobart: gutenberg.net.au/ebooks06/06005…

Famously, contact with the outside world ended very, very badly for the Aboriginal people of Tasmania.

Two centuries after Tasman, the British governor lead an attempted genocide to secure the island for European livestock farming.

That's essentially the plot of Liu Cixin's "Three-Body Problem" trilogy -- a message to extraterrestrials may announce our presence and invite invasion.

It's impossible to know the motivations or technological abilities of ETs, so it may be best to stay in the shadows.

At the very least, any civilization looking to invest vast resources in creating a long-lasting beacon would want to be extremely confident that doing so wasn't encouraging disaster.

If you hypothesize that any technological civilization will have experienced resource scarcity, competition and conflict in its rise, it's likely they'd be pretty circumspect about such a project.

We know this because a lot of SETI researchers here on Earth are very suspicious of sending such messages, and at minimum think it should only be done after extensive public debate that we really haven't had.

So that's what I think brings the odds of Fermi's calculation (best formalized in the Drake equation en.wikipedia.org/wiki/Drake_equ…) down to levels more consistent with the seeming emptiness of space:

There are *a lot* of technological civilizations out there, in the millions or billions, but almost all of them are far too distant for passive observation to even be possible in the period when they're "radio loud".

If there are any civilizations close enough to be observable, their commitment to sending messages is likely to be as ambivalent and half-hearted as ours, so the odds of us seeing anything are pretty low.

And for what it's worth in just the short span of time we've been looking, we may have seen some hints of things suggestive of extraterrestrial life.

The Wow! Signal is a very odd transmission in the radio "water hole" picked up in 1977: en.wikipedia.org/wiki/Wow!_sign…

Researchers have argued ever since about what the hell it was. There was no information we were able to decode from it. But arguably that's exactly what you'd expect from a radio message from ETs that didn't quite hit right.

One strong argument against an ET origin of the signal is the classic scientific one that it wasn't replicable -- there was just one Wow! Signal.

But there was also just one Arecibo Message, and it definitely happened.

The same goes for 'Oumuamua, the weird object that passed through the solar system recently and that the chair of Harvard's astronomy department has argued could be an extraterrestrial probe: newyorker.com/news/q-and-a/h…

I think the universe is not so much devoid of life, as teeming with life at very low densities -- so low that in most circumstances it's going to be impossible for us to ever contact each other, even if we want to.

We're not in a desert, we're in a dark forest -- vast, full of life, magical but forbidding. (ends)