Is there intelligent extraterrestial life?

Posted by sam – September 3, 2017

My commonsense position on intelligent extraterrestial life: it surely exists, but very likely its lightcone and our lightcone don’t intersect, so we can’t interact with it because it’s too far away, too long ago or too far in the future. In this way aliens are like God: the universe in which they exist isn’t necessarily observationally distinct from the one in which they don’t.

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  1. sam says:
    October 10, 2018 at 11:40

    Facebook comment thread:

    Vadim Kulikov: Why, do you think our own lightcone is too small? I think all versions of the Fermi paradox imply that our lightcone is big enough to contain other intelligent life.

    Sam Hardwick: You can set constants in the Drake equation so that the number N of galactic civilizations we can expect to communicate with is < 1. My position amounts to saying that N << 1, but if you remove some of the constraints, like galactic locality or simultaneity with us, N >> 1.

    Sampo Tiensuu: I would say that this not a question about whether our light cones intersect or not.

    First, it is not enough for our light cones to intersect. For a signal to travel from us to them or from them to us, we need to be in each other’s light cones.

    Second, even if there is other intelligent life in our light cone, it does not mean that any kind of interaction is possible, because it can be very hard to send a signal that is detectable even a few light years away.

    I think it is very likely that there is a lot of intelligent life in our light cone and it can still be very unlikely that we can ever observe them or that they can observe us.

    Vadim Kulikov: I just realised that no matter where they are, if we wait long enough, they will be in our lightcone! They might be extinct by that time of course.

    All lightcones intersect. Unless the world is super-non-Euclidean.

    Sam Hardwick: Doesn’t the universe expand fast enough that parts of it are forever inaccessible to each other?

    “In the future, light from distant galaxies will have had more time to travel, so additional regions will become observable. However, due to Hubble’s law, regions sufficiently distant from the Earth are expanding away from it faster than the speed of light (special relativity prevents nearby objects in the same local region from moving faster than the speed of light with respect to each other, but there is no such constraint for distant objects when the space between them is expanding; see uses of the proper distance for a discussion) and furthermore the expansion rate appears to be accelerating due to dark energy. Assuming dark energy remains constant (an unchanging cosmological constant), so that the expansion rate of the Universe continues to accelerate, there is a “future visibility limit” beyond which objects will never enter our observable universe at any time in the infinite future, because light emitted by objects outside that limit would never reach the Earth.”

    Vadim Kulikov: Ahaa. Waw. I didn’t know it goes this way. Useful facebook thread. So it is “super non-Euclidean” in some sense

      

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