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Somewhere out there in that vast universe,

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there must surely be countless
other planets teeming with life,

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but why don't we see any evidence of it?

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Well, this is the famous question
asked by Enrico Fermi in 1950:

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"Where is everybody?"

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Conspiracy theorists claim
that UFOs are visiting all the time

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and the reports are just being covered up,

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but honestly, they aren't very convincing.

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But that leaves a real riddle.

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In the past year,
the Kepler space observatory

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has found hundreds of planets
just around nearby stars,

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and if you extrapolate that data,

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it looks like there could be
half a trillion planets

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just in our own galaxy.

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If any one in 10,000 has conditions
that might support a form of life,

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that's still 50 million possible
life-harboring planets

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right here in the Milky Way.

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So here's the riddle.

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Our Earth didn't form

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until about 9 billion years
after the Big Bang.

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Countless other planets in our galaxy
should have formed earlier

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and given life a chance to get underway

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billions or certainly
many millions of years

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earlier than happened on Earth.

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If just a few of them
had spawned intelligent life

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and started creating technologies,

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those technologies
would have had millions of years

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to grow in complexity and power.

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On Earth,

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we've seen how dramatically
technology can accelerate

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in just 100 years.

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In millions of years,
an intelligent alien civilization

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could easily have spread out
across the galaxy,

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perhaps creating giant
energy-harvesting artifacts,

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or fleets of colonizing spaceships,

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or glorious works of art
that fill the night sky.

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At the very least, you'd think
they'd be revealing their presence,

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deliberately or otherwise,

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through electromagnetic signals
of one kind or another.

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And yet we see no convincing
evidence of any of it.

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Why?

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Well, there are numerous possible answers,

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some of them quite dark.

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Maybe a single,
superintelligent civilization

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has indeed taken over the galaxy,

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and has imposed strict radio silence

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because it's paranoid
of any potential competitors.

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It's just sitting there
ready to obliterate

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anything that becomes a threat.

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Or maybe they're not that intelligent.

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Or perhaps, the evolution
of an intelligence

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capable of creating
sophisticated technology

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is far rarer than we've assumed.

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After all,

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it's only happened once on Earth

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in 4 billion years.

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Maybe even that was incredibly lucky.

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Maybe we are the first
such civilization in our galaxy.

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Or, perhaps, civilization carries with it

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the seeds of its own destruction

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through the inability to control
the technologies it creates.

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But there are numerous
more hopeful answers.

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For a start, we're not looking that hard,

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and we're spending a pitiful
amount of money on it.

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Only a tiny fraction
of the stars in our galaxy

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have really been looked at closely
for signs of interesting signals.

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And perhaps, we're not looking
the right way.

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Maybe as civilizations develop,

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they quickly discover
communication technologies

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far more sophisticated and useful
than electromagnetic waves.

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Maybe all the action takes place

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inside the mysterious
recently discovered dark matter,

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or dark energy,

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that appear to account
for most of the universe's mass.

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Or maybe we're looking at the wrong scale.

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Perhaps intelligent civilizations
come to realize

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that life is ultimately just complex
patterns of information

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interacting with each other
in a beautiful way,

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and that can happen
more efficiently at a small scale.

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So just as on Earth, clunky stereo systems
have shrunk to beautiful, tiny iPods,

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maybe intelligent life itself,

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in order to reduce its footprint
on the environment,

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has turned itself microscopic,

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so the Solar System
might be teeming with aliens,

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and we're just not noticing them.

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Maybe the very ideas in our heads
are a form of alien life.

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Well, okay, that's a crazy thought.

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The aliens made me say it.

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But it is cool that ideas do seem
to have a life all of their own,

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and that they outlive their creators.

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Maybe biological life
is just a passing phase.

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Well, within the next 15 years,

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we could start seeing
real spectroscopic information

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from promising nearby planets

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that will reveal just how
life-friendly they might be.

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And meanwhile SETI,

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the Search for
Extra-Terrestrial Intelligence,

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is now releasing its data to the public

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so that millions of citizen scientists,
maybe including you,

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can bring the power of the crowd
to join the search.

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And here on Earth,
amazing experiments are being done

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to try to create life from scratch,

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life that might be very different
from the DNA forms we know.

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All of this will help us understand

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whether the universe is teeming with life

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or, whether indeed,

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it's just us.

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Either answer, in its own way,

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is awe-inspiring,

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because even if we are alone,

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the fact that we think and dream,

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and ask these questions

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might yet turn out to be
one of the most important facts

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about the universe.

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And I have one more piece
of good news for you.

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The quest for knowledge
and understanding never gets dull.

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It doesn't. It's actually the opposite.

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The more you know,

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the more amazing the world seems.

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And it's the crazy possibilities,
the unanswered questions,

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that pull us forward.

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So, stay curious.