David N Spergel
Director: Center for Computational Astrophysics, Flatiron
Charles Young Professor Emeritus, Princeton University
Co-Chair: NASA WFIRST Form. Science Working Group
Lecturer, “Imagining Other Earths”, Free COURSERA lectures https://www.coursera.org/lecture/life-on-other-planets/welcome-dahsG

How will humanity first discover ET Life?
Best guess: Biosignature

Why we will need to wait for advanced lifeforms to contact us: 

Nearby Sun-like stars differ in age by billions of years.  Life on nearby exoplanets is likely a billion years older or billion years younger than on Earth
Timescale for technological evolution is much more rapid.  E.g., we now commute primarily through compressed signals on optical  fibers.  Compressed signals look like noise--- can’t eavesdrop on  advanced civilizations.

There's a starman waiting in the sky He'd like to come and meet us But he thinks he'd blow our minds There's a starman waiting in the sky He's told us not to blow it Cause he knows it's all worthwhile -  David Bowie

We can detect simpler lifeforms through their biosignatures
Oxygen, Ozone, Methane: signature of active biochemistry
Need to develop the ability  to image and  characterize the atmospheres of exoplanets
Cosmology drove the design of telescopes for the past century: Hale’s 100in to the  James Webb Space Telescope.  Search for the signatures of life will drive the design of telescopes for the next century
WFIRST will be both a powerful telescope for cosmology (Hubble-class telescope with 100x field of view) and for advancing study of exoplanets

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