Name: 【TED】Stephen Webb: Where are all the aliens? (Where are all the aliens? | Stephen Webb)
Uploaded: 2018-08-16T16:33:44.000Z
Duration: 13 min 19 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

playing in the street with a friend who was a couple of years older,

and we saw a featureless silver disc hovering over the houses.

and then it shot away incredibly quickly.

I got angry it was ignoring the laws of physics.

I was coming out of the pub after a few drinks."

I stopped him there. I said, "I can explain that sighting."

Psychologists have shown we can't trust our brains

or that my brain misinterpreted the data my eyes were giving it?

Why don't we see flying saucers flitting around?

why don't we see life out there in the cosmos?

and I've discussed it with dozens of experts

from different disciplines over the past three decades.

Frank Drake began searching for alien signals back in 1960 --

this lack of evidence for any alien activity gets more puzzling

because we should see them, shouldn't we?

If we represent the age of the universe by one year,

then our species came into being about 12 minutes before midnight,

Western civilization has existed for a few seconds.

Extraterrestrial civilizations could have started in the summer months.

developing a level of technology more advanced than ours,

but tech based on accepted physics though,

I'm not talking wormholes or warp drives -- whatever --

just an extrapolation of the sort of tech that TED celebrates.

That civilization could program self-replicating probes

to visit every planetary system in the galaxy.

If they launched the first probes just after midnight one August day,

Intergalactic colonization isn't much more difficult,

A civilization from any one of millions of galaxies

but wouldn't aliens engage in some recognizable activity --

put worldlets around a star to capture free sunlight,

or just shout out to the universe, "We're here"?

It's a puzzle because we do expect these civilizations to exist, don't we?

After all, there could be a trillion planets in the galaxy --

You don't need any special knowledge to consider this question,

and I've explored it with lots of people over the years.

And I've found they often frame their thinking

in terms of the barriers that would need to be cleared

if a planet is to host a communicative civilization.

And they usually identify four key barriers.

We need a terrestrial planet in that just right "Goldilocks zone,"

In 2016, astronomers confirmed there's a planet in the habitable zone

so close that Breakthrough Starshot project plans to send probes there.

Some will be too close to a star and they'll fry,

some will be too far away and they'll freeze.

The basic building blocks of life aren't unique to Earth:

complex organic molecules in interstellar dust clouds,

we just don't know how they combine to create life,

and presumably there will be worlds on which life doesn't start.

The development of technological civilization is a third barrier.

Some say we already share our planet with alien intelligences.

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【TED】Stephen Webb: Where are all the aliens? (Where are all the aliens? | Stephen Webb)

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