How old could alien civilizations be? | Space with Sarah #4 | @spacewsarah

Hi and welcome to Space with Sarah. When I go out into the world and tell people
that I’m an astrophysicist I often get a ton of really interesting questions. Today we’re going to talk about when an earth-like
planet could have formed. Many people, myself included, seem really
fascinated by the idea of life elsewhere in the Universe. The enormous amount of stars, galaxies and
planets that exist almost makes it weird to think that there wouldn’t be life elsewhere
– and also, why would we here on Earth be special and be the only life that exists in
the entire Universe? One of the really interesting discoveries
in astronomy within the last twenty years is that we’re finding more and more planets around
other stars than the Sun. We call these extrasolar planets or exoplanets. For life to exist, there are a lot of different
variables that we need to investigate. For example, does the planet that we found
have a rocky surface so that we could live on it, is it far enough from its sun to have
liquid water, and also does it have an atmosphere. A big problem in the search for life is that
we don’t know the probability of life starting if the conditions are there for life to start. In other words, biologists have never been
able to make life out of non-life in a laboratory, These are all a lot of unknowns and when we
consider life elsewhere, intelligent life would be a lot more interesting to find. A question I like to think about is: at what
point in time in the history of the Universe could a planet like Earth have formed? Our own solar system is only 4.6 billion years
old but the Universe is a lot older it’s 13.8 billion years old. However the Big Bang mostly produced Hydrogen
and Helium and only traces of a few of the heavier elements. As we would have a really hard time living on
a gaseous planet. That raises the question of at what point
in time in the history of the Universe did we have enough elements such as oxygen, silicon
and iron which are the majority of the elements that make up Earth’s crust. Here’s the crazy
part, these elements need to be produced in the interiors of stars through fusion, and
not only that these stars need to actually explode or die to expel all these elements
out into space. This is a whole subject which I’ll discuss a lot more in a future video, but the point here is that Earth could not have
formed until enough stars in the Universe had already exploded. This means that everything we touch here on
Earth, everything that we’re made of is made either in the Big Bang, in the core of a star
or in a stellar explosion. As more time passes after the Big Bang, more
and more stars will have time to explode and put out their elements. Research definitely shows that there’s
a correlation between the time passed since the Big Bang and the amount of heavier elements
out there in space. The planet hunting Kepler telescope has found
more than 2000 planets orbiting other stars than our Sun, and my favorite system that
it’s found so far consists of a star with five rocky planets orbiting it. The reason that I really like this system
is because it’s 6.6 billions years older than our own solar system, meaning that it formed
only 2.6 billion years after the big bang. These five rocky planets, probably don’t have
life because they are way too close to their host star, that means it would be really hot
on their surface. However, this demonstrates that planetary
systems could have formed a lot earlier in the history of the Universe than our solar
system. Say for a moment that a planetary system did
exist that is just as old, where the conditions for life were there, that begs the question,
how intelligent would their civilization be if they have evolved for billions of years
longer than life here on Earth. We don’t actually know the answer to that
question, but it’s still fascinating to think about, right? Thanks for watching Space with Sarah. If you are still curious about the Universe,
please subscribe to the channel and as always: keep wondering.


  1. Black Hole Universe said:

    Our Universe is alot older then 13.8 billion years, however, perfect conditions for human-like forms to live is an area of only 236.000 light year radius from the center of Earth, where local gravitational field is very small.

    Later (as Hubble ovservation showed) light sign changes from negative to positive (galaxies are becoming redshifted) and gravity grows together with distance from center of Our Universe, making it harder and harder for life to happen.

    May 11, 2017
  2. Rasmus Visgaard said:

    The difference in DNA between apes and humans, is very small (98,8% [1]), so just a small difference in DNA in favour of intelligent life outside of the earth, could make a huge impact on the idea of intelligent life. If say, intelligent life outside the earth is smarter than humans, why have they not contacted us yet? Are we considered "boring" or "not worth it"? Is their technology not developed enough? What does that say about our technology? I would love to hear your thoughts on this Sarah. Your video was awesome, but that is only the beginning of it!


    May 11, 2017
  3. Pedro Pinheiro said:

    Amazing video, Sarah <3 Would've been cool to mention the Miller-Urey Experiment 😀

    May 11, 2017
  4. Enrique Olvera said:

    I can't imagine how our technology will be 6600 million years into the future, it's just mindblowing how fast we are progressing

    May 11, 2017
  5. x_401_err0r_x said:

    It's mind-boggling to envisage the technological advancement of the next 1000 years, never mind millions or billions of years into the future considering our own exponential development of the last century.

    May 12, 2017
  6. wintardable said:

    Super vid, Sarah! Keep it up 🙂 "Two possibilities exist: either we are alone in the Universe or we are not. Both are equally terrifying."

    May 12, 2017
  7. Martin Glob said:

    Loved It!

    May 13, 2017
  8. james minor said:

    i saw you on Fraser khan i have subscribed and thanks you for all you do

    May 20, 2017
  9. AstroFocus said:

    Fantastic video 😀 Just wish I gained these much subscribers as fast as you 😉

    May 20, 2017
  10. Peter Houle said:

    interesting content, thank you! (I just saw you on Fraser Cain's latest vid)

    May 21, 2017
  11. Vulcan Sky said:

    Will the Milky Way ever collide with any galaxy outside the local group?

    May 21, 2017
  12. UltimaShadrax said:

    Very well done.Thanks, I will look forward to seeing more content.

    May 21, 2017
  13. TheCimbrianBull said:

    Great video! Very informative and well explained. BTW, Fraser Cain brought me here. 🙂

    May 22, 2017
  14. JPW said:

    Fraser send me, nice content you have.

    May 22, 2017
  15. James Makoni said:

    13 billion years doesn't sound like much. Until you realise that's 13 thousand million years.

    Assuming that system you mentioned is Trappist 1, I have a suspicion life on those planets "could" evolve down a different pathway which wither negates the effects of heavy radiation from a red dward…. or even uses the radiation beneficially ( mother nature has a habit of trolling us for the lulz ).

    That being said, keep the videos coming. 🙂

    May 26, 2017
  16. Dreamcatcher said:


    June 7, 2017
  17. Rajeev Mohan said:

    😊😊..How do u determine the age of the universe and solar system…

    June 23, 2017
  18. Savage Historian said:

    doesn't the fermi paradox and occams razor make the probability of finding intelligent life near 0 ?

    June 26, 2017
  19. Coffee in Code out said:

    I love this video really ansered a lot of questions. Thank you and keep posting!

    July 20, 2017
  20. DigitizedSelf said:

    Very nice video but I felt like you dodged the question a little. Is there a theoretical lower age at which the earliest formation of rocky planets could have taken place? Or possibly an estimate from simulations about when they were likely to have formed?

    September 4, 2017
  21. Larry Beckham said:


    September 18, 2017
  22. Catira App said:

    I am looking into graduate programs at Columbia University and that is how I ended up here I like space.

    January 17, 2018
  23. AskAstronomy said:

    I think an interesting follow-up to this video would be a video on the Fermi Paradox!

    January 21, 2018
  24. Eliu Saucedo said:

    The "BIG BANG" LMFAO I'm out!!

    February 16, 2018
  25. Jón Frímann Jónsson said:

    Some population II stars might support carbon based life. But far as I can see in the data life seems to be mostly common around population III stars. G, K, F type of stars only, everything else is either too cold or too hot.

    May 11, 2018
  26. Doodelay said:

    Fantastic intro and very impressive video production. Found you on Fraser and decided to check you out, not disappointed but I think you could've gone farther with this topic and looked at in depth.

    June 6, 2019

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