21 ms·

Tangential to the article, but I’m not sure why more isn’t mentioned about what I consider to be the most likely reason we haven’t been visited by aliens: they

Tangential to the article, but I’m not sure why more isn’t mentioned about what I consider to be the most likely reason we haven’t been visited by aliens: they probably exist somewhere due to the sheer size of the universe, but the speed of light is indeed the fundamental limit to classical information transfer as our current understanding of physics predicts, and therefore we are simply too far away from any sort of intelligence that exists out there to contact or reach us. It’s a simple and boring explanation but from my perspective also the most likely.

cgriswald 6y ago
The solution to distance isn’t energy; it’s time. Even at speeds much lower than the speed of light, a civilization could have spread across or explored the Milky Way in a few millions of years. These needn’t have been biological creatures. Von Neumann probes, “Genesis” machines, or just flinging rocks with sensors on them to tour the stars would do the trick.
- blueblisters 6y ago
  What would motivate a civilization to undertake such an experiment? A probe a 50,000 light years away would take 50,000 years to send back any meaningful information. Unless alien life-spans are significantly longer than humans, I would think this would probably not be funded by their science department.
  - RobertoG 6y ago
    A probe of the sophistication of a Von Newman machine, that can reproduce, would be the alien in itself. A network of such probes would be a civilization.
    - LargoLasskhyfv 6y ago
      https://en.wikipedia.org/wiki/Code_of_the_Lifemaker https://en.wikipedia.org/wiki/Code_of_the_Lifemaker http://www.baen.com/chapters/W200203/0743435265___0.htm http://www.baen.com/chapters/W200203/0743435265___0.htm :-)
      - RobertoG 6y ago
        Thanks! I'm going to read it.
  - sterlind 6y ago
    Von Neumann probes would be great at asteroid mining. If you just let the probes keep going rather than limiting their distance, they'd cover the 50k light years easily. Not much overhead on the civilization.
  - GoblinSlayer 6y ago
    They spent 50000 years exploring space, we spent 50000 years waging wars. Who spent their time better?
cronix 6y ago
> but the speed of light is indeed the fundamental limit to classical information transfer as our current understanding of physics predicts I used to think that as well, but with all of the recent proof of quantum entanglement, I'm not so sure anymore. https://www.extremetech.com/extreme/295013-scientists-capture-photographic-proof-of-quantum-entanglement https://www.extremetech.com/extreme/295013-scientists-captur...
- scythmic_waves 6y ago
  My (relatively uninformed) understanding was that you couldn't transfer information via quantum entanglement. Is that not correct?
  - cronix 6y ago
    This is not my field, but it seem if you can spin 1 particle in a known direction and the entangled "partner" particle spins the exact opposite direction, then why not? Basically everything would just be reversed with a 1 being a 0 and a 0 being a 1 on the receiving end. I know both the Chinese and American governments are working on quantum entanglement as a communication mechanism and the Chinese have had some success between satellites. Basically a real time wireless internet. Edit: better link for Chinese experiments from Science Mag. https://www.sciencemag.org/news/2020/02/quantum-internet-closer-physicists-stretch-spooky-link-between-atoms https://www.sciencemag.org/news/2020/02/quantum-internet-clo... https://finance.yahoo.com/news/chinas-experiment-quantum-communication-brings-093000332.html https://finance.yahoo.com/news/chinas-experiment-quantum-com... https://newatlas.com/telecommunications/us-government-blueprint-national-quantum-internet/ https://newatlas.com/telecommunications/us-government-bluepr...
    - IgorPartola 6y ago
      Because you don’t get to choose which way the particle spins when creating an entangled pair.
    - matmatmatmat 6y ago
      As others have said, the fundamental problem is that all you can deduce is that whatever the spin of your particle is, the other particle has the opposite spin. You cannot determine the spin of your particle in order to affect the spin of the other particle.
avz 6y ago
I don't find the argument that distances are too great for intelligence to meet particularly convincing. At its core lies unjustified extrapolation that the ratio of average lifespan to typical interstellar distance - a pure accident of Earthly biology - somehow extends to the whole universe. The key quantity on which the argument hinges is T * c / D where T is the average lifespan of the intelligent being in question, c is the speed of light and D is a typical separation between stars in a region of interest. In our stellar neighborhood there are about 0.004 stars per cubic light year [1], so if we choose to measure D as the reciprocal of the cubic root of stellar density then D is about 6.3 light years which is of the same order of magnitude as the distance to Proxima Centauri (~4.2 ly). This quantity varies somewhat, e.g. global clusters have about 0.4 stars per cubic parsec [2] which is more than 0.01 stars per cubic light year for D of 4.4 ly. In case of humans, T is about 79 years. We don't know anything about any alien lifeforms, but even among lifeforms on Earth T varies significantly. For example, Bowhead whales can live more than 200 years [3]. Traveling 4 ly at 5% of the speed of light is a possibility for such creatures. Moreover, entities with artificial intelligence could live (function?) significantly longer. Possibly forever. [1]: https://en.wikipedia.org/wiki/Stellar_density https://en.wikipedia.org/wiki/Stellar_density [2]: https://en.wikipedia.org/wiki/Globular_cluster https://en.wikipedia.org/wiki/Globular_cluster [3]: https://en.wikipedia.org/wiki/Bowhead_whale https://en.wikipedia.org/wiki/Bowhead_whale
- nobody9999 6y ago
  >The key quantity on which the argument hinges is T * c / D I'd think that it's also important to have a component that quantifies the lifetime of a technologically advanced civilization, as the universe isn't just separated by space, but also by vast expanses of time as well. I'm not belittling your example, just trying pointing out that when speculating in this area, it's useful to include a time component related to civilizations as well as an individual lifetime component.
at_a_remove 6y ago
This has been my basic take on it. However, if you want a point of concern, I'll throw out some alternatives. I'm going to ignore generation ships, because those seem a trifle unlikely (too complex, rather cruel to the inhabitants), but let's imagine some embryo-laden carriers, freeze-dried aliens, and von Neumann probes. Now, again, that's still a long way for very little gain. There's nothing physical you could bring back to your civilization that would be "worth" the trip, but what about some irrational civilizations? Religious zealots, or just a large enough portion of a technologically advanced society that says, "Screw it, let's hurl some madly self-replicating probes out into the spiral arm." Ninety-nine percent of their civilization might think that is a terrible idea (or pick your proportion), but there only needs to be a few to pull it off. Why are we not seeing the von Neumann probes? I will admit that the other scenarios are less likely. But where are they? Even at a ten thousandth the speed of light they would have swarmed the galaxy, replicating down one spiral arm, into the core, and back out along the remaining arms.
- GoblinSlayer 6y ago
  The solar system is between arms.

cgriswald 6y ago

The solution to distance isn’t energy; it’s time. Even at speeds much lower than the speed of light, a civilization could have spread across or explored the Milky Way in a few millions of years. These needn’t have been biological creatures. Von Neumann probes, “Genesis” machines, or just flinging rocks with sensors on them to tour the stars would do the trick.

blueblisters 6y ago
What would motivate a civilization to undertake such an experiment? A probe a 50,000 light years away would take 50,000 years to send back any meaningful information. Unless alien life-spans are significantly longer than humans, I would think this would probably not be funded by their science department.
- RobertoG 6y ago
  A probe of the sophistication of a Von Newman machine, that can reproduce, would be the alien in itself. A network of such probes would be a civilization.
  - LargoLasskhyfv 6y ago
    https://en.wikipedia.org/wiki/Code_of_the_Lifemaker https://en.wikipedia.org/wiki/Code_of_the_Lifemaker http://www.baen.com/chapters/W200203/0743435265___0.htm http://www.baen.com/chapters/W200203/0743435265___0.htm :-)
    - RobertoG 6y ago
      Thanks! I'm going to read it.
- sterlind 6y ago
  Von Neumann probes would be great at asteroid mining. If you just let the probes keep going rather than limiting their distance, they'd cover the 50k light years easily. Not much overhead on the civilization.
- GoblinSlayer 6y ago
  They spent 50000 years exploring space, we spent 50000 years waging wars. Who spent their time better?

cronix 6y ago

> but the speed of light is indeed the fundamental limit to classical information transfer as our current understanding of physics predicts I used to think that as well, but with all of the recent proof of quantum entanglement, I'm not so sure anymore. https://www.extremetech.com/extreme/295013-scientists-capture-photographic-proof-of-quantum-entanglement https://www.extremetech.com/extreme/295013-scientists-captur...

scythmic_waves 6y ago
My (relatively uninformed) understanding was that you couldn't transfer information via quantum entanglement. Is that not correct?
- cronix 6y ago
  This is not my field, but it seem if you can spin 1 particle in a known direction and the entangled "partner" particle spins the exact opposite direction, then why not? Basically everything would just be reversed with a 1 being a 0 and a 0 being a 1 on the receiving end. I know both the Chinese and American governments are working on quantum entanglement as a communication mechanism and the Chinese have had some success between satellites. Basically a real time wireless internet. Edit: better link for Chinese experiments from Science Mag. https://www.sciencemag.org/news/2020/02/quantum-internet-closer-physicists-stretch-spooky-link-between-atoms https://www.sciencemag.org/news/2020/02/quantum-internet-clo... https://finance.yahoo.com/news/chinas-experiment-quantum-communication-brings-093000332.html https://finance.yahoo.com/news/chinas-experiment-quantum-com... https://newatlas.com/telecommunications/us-government-blueprint-national-quantum-internet/ https://newatlas.com/telecommunications/us-government-bluepr...
  - IgorPartola 6y ago
    Because you don’t get to choose which way the particle spins when creating an entangled pair.
  - matmatmatmat 6y ago
    As others have said, the fundamental problem is that all you can deduce is that whatever the spin of your particle is, the other particle has the opposite spin. You cannot determine the spin of your particle in order to affect the spin of the other particle.

avz 6y ago

I don't find the argument that distances are too great for intelligence to meet particularly convincing. At its core lies unjustified extrapolation that the ratio of average lifespan to typical interstellar distance - a pure accident of Earthly biology - somehow extends to the whole universe. The key quantity on which the argument hinges is T * c / D where T is the average lifespan of the intelligent being in question, c is the speed of light and D is a typical separation between stars in a region of interest. In our stellar neighborhood there are about 0.004 stars per cubic light year [1], so if we choose to measure D as the reciprocal of the cubic root of stellar density then D is about 6.3 light years which is of the same order of magnitude as the distance to Proxima Centauri (~4.2 ly). This quantity varies somewhat, e.g. global clusters have about 0.4 stars per cubic parsec [2] which is more than 0.01 stars per cubic light year for D of 4.4 ly. In case of humans, T is about 79 years. We don't know anything about any alien lifeforms, but even among lifeforms on Earth T varies significantly. For example, Bowhead whales can live more than 200 years [3]. Traveling 4 ly at 5% of the speed of light is a possibility for such creatures. Moreover, entities with artificial intelligence could live (function?) significantly longer. Possibly forever. [1]: https://en.wikipedia.org/wiki/Stellar_density https://en.wikipedia.org/wiki/Stellar_density [2]: https://en.wikipedia.org/wiki/Globular_cluster https://en.wikipedia.org/wiki/Globular_cluster [3]: https://en.wikipedia.org/wiki/Bowhead_whale https://en.wikipedia.org/wiki/Bowhead_whale

nobody9999 6y ago
>The key quantity on which the argument hinges is T * c / D I'd think that it's also important to have a component that quantifies the lifetime of a technologically advanced civilization, as the universe isn't just separated by space, but also by vast expanses of time as well. I'm not belittling your example, just trying pointing out that when speculating in this area, it's useful to include a time component related to civilizations as well as an individual lifetime component.

at_a_remove 6y ago

This has been my basic take on it. However, if you want a point of concern, I'll throw out some alternatives. I'm going to ignore generation ships, because those seem a trifle unlikely (too complex, rather cruel to the inhabitants), but let's imagine some embryo-laden carriers, freeze-dried aliens, and von Neumann probes. Now, again, that's still a long way for very little gain. There's nothing physical you could bring back to your civilization that would be "worth" the trip, but what about some irrational civilizations? Religious zealots, or just a large enough portion of a technologically advanced society that says, "Screw it, let's hurl some madly self-replicating probes out into the spiral arm." Ninety-nine percent of their civilization might think that is a terrible idea (or pick your proportion), but there only needs to be a few to pull it off. Why are we not seeing the von Neumann probes? I will admit that the other scenarios are less likely. But where are they? Even at a ten thousandth the speed of light they would have swarmed the galaxy, replicating down one spiral arm, into the core, and back out along the remaining arms.

GoblinSlayer 6y ago
The solar system is between arms.