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Grabby Aliens (2021)

grabbyaliens.com

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Re: Grabby Aliens (2021)

#41

Post by AnimalMuppet »

GavinB wrote: post #10

This is a compelling theory, especially the implication that humans are early. I do wonder whether we should see the evidence of spheres of growing alien influence out in the stars, but instead we see a highly uniform universe in all directions. This would indicate a few possibilities: 1. Expanding alien civilizations are relatively low impact and don't collect all of the energy of stars in ways that are visible to o…

Aliens collecting all the light/electromagnetic radiation from stars would be an interesting way to get dark matter. That's one place it could fit.

And, if our theories are right, we're at 4.9% regular matter and 26.8% dark matter, so dark matter is five times as much as regular matter, so that's a lot of aliens...

Re: Grabby Aliens (2021)

#42

Post by Qem »

cryptoz wrote: post #38
Charon77 wrote: post #32

Earlier quoted context omitted.

If a planet in the nearest star harbors life form that launched a rocket, would we know?

No, we wouldn't know today. But this is knowable in about 50 years or so, if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. This may be enough to find a spacefaring civilization. (sure, rockets aren't 1km big, but they do leave big traces. maybe we could see that)

> if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves.

It doesn't scale well. The probe would be able to observe a carefully chosen extrasolar planetary system in the opposite direction in relation to the sun. If you want to observe a second system, it's necessary to launch a second probe 550 AU in another direction. You can't change targets just by rotating the probe, given its lens is the sun.

Re: Grabby Aliens (2021)

#43

Post by eightysixfour »

> While the current date is 13.8 billion years after the Big Bang, the average star will last over five trillion years.

That does not seem right. Isn't the lifespan of a star between 100m and 100b years or so?

Re: Grabby Aliens (2021)

#44

Post by defrost »

cryptoz wrote: post #38
Charon77 wrote: post #32

Earlier quoted context omitted.

If a planet in the nearest star harbors life form that launched a rocket, would we know?

No, we wouldn't know today. But this is knowable in about 50 years or so, if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. This may be enough to find a spacefaring civilization. (sure, rockets aren't 1km big, but they do leave big traces. maybe we could see that)

As Qem mentioned, and as laid out on page 7 of the source paper:

    A significant difference of the solar gravitational lens from a conventional telescope is that the gravitational lens telescope is not in any practical sense pointable.

    For the telescope at a distance F from the sun to be re-aimed to image a new target 1° away, it would have to move a distance of (π/180°)F, which is 10 astronomical units at the minimum focal distance-- a lateral distance equivalent to the distance from Earth to Saturn.

    This means that, in practice, such a telescope is not able to be repointed.

    Thus, a telescope at the gravitational focus is necessarily going to be a singlepurpose telescope, with the target of observation selected before the mission is launched.

    A gravitational focus mission can’t be used as a telescope to search for a target: such a mission must be with the objective to observe a target whose position is already known.
Mission to the Gravitational Focus of the Sun: A Critical Analysis

Geoffrey A. Landis, NASA John Glenn Research Center

https://arxiv.org/ftp/arxiv/papers/1604/1604.06351.pdf

Re: Grabby Aliens (2021)

#45

Post by cryptoz »

Qem wrote: post #42
cryptoz wrote: post #38

Earlier quoted context omitted.

No, we wouldn't know today. But this is knowable in about 50 years or so, if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. This may be enough to find a spacefaring civilization. (sure, rockets aren't 1km big, but they do leave big traces. maybe we could see that)

> if we send probes to ~550AU and use the Sun as a gravitational lens; we will then be able to get high-res (1km resolution?) photos/videos of nearby extrasolar planets themselves. It doesn't scale well. The probe would be able to observe a carefully chosen extrasolar planetary system in the opposite direction in relation to the sun. If you want to observe a second system, it's necessary to launch a second probe 550…

Oh yeah, I'm aware that you'll need multiple probes - but I imagine we could send 50 or 100 of these things starting in like 20-30 years once some of the required engineering on propulsion systems etc is done. Assuming we have the will and money to send 1, I think we'd have the will and money to send dozens.

Re: Grabby Aliens (2021)

#46

Post by dang »

Related:

Grabby Aliens: A Resolution to the Fermi Paradox - https://news.ycombinator.com/item?id=33402628 - Oct 2022 (334 comments)

Grabby Aliens - https://news.ycombinator.com/item?id=26502232 - March 2021 (176 comments)

A Simple Model of Grabby Aliens - https://news.ycombinator.com/item?id=26045731 - Feb 2021 (80 comments)

Re: Grabby Aliens (2021)

#47

Post by Kostic »

fouc wrote: post #2

What I found most interesting about this model was the implication that humans are possibly one of the earliest sentient spacefaring species to have appeared so far. Which explains why we haven't seen any other signs of extraterrestrial intelligence yet.

Spacefaring is very generious. We still have to make a trip between two planets, not to mention two stars.

Re: Grabby Aliens (2021)

#49

Post by mapmeld »

My go-to counterargument for this is that galaxies are really far apart (from us to Andromeda is 25x the diameter of the Milky Way). If you haven't developed FTL travel, it's a long haul with very little benefit on the way.

Re: Grabby Aliens (2021)

#50

Post by eschaton »

eightysixfour wrote: post #43

> While the current date is 13.8 billion years after the Big Bang, the average star will last over five trillion years. That does not seem right. Isn't the lifespan of a star between 100m and 100b years or so?

I think it depends on what you mean by “last,” a star might “last” even longer than 5×10^12 years before the last component nucleons of its remnant evaporate. If you consider how long a star lasts to be how long it emits around the same amount of energy until becoming another class of object the time will be shorter.

Sol will grow large and red in another 4×10^9 years or so, then after that phase it’ll leave a stellar remnant like a brown dwarf or neutron star, which will last another period of time. How long did Sol last?

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