[crystaln]

A widespread theory among et believers is that nuclear explosions bring the attention of et intelligence around the universe as a sign of sufficiently advanced life to investigate, and that aliens are here to make sure we develop without self-destructing and join the intergalactic world peacefully.

[cryptonector]

In reality other advanced civilizations elsewhere and elsewhen in our galaxy are as constrained by the speed of light as we are, thus they can't come here as we can't go there.

[anomaloustho]

Isaac Arthur has put it in a way that resonated with me. If you live in a universe that has FTL, it’s scarier in a lot ways. It means the really dangerous bad guys in the other galaxy can reach you. If you live in a world without FTL, it makes things happen really slowly and over generations. That’s not as fun and exciting, but it also severely limits the amount of bad guys that can get to you.

And any bad guy that can even reach you basically means you’re already dead if they so choose.

[arethuza]

Doesn't FTL also imply time travel - which probably isn't a good thing?

[lawlessone]

I think wormholes and warp sort of get around it by having the FTL traveler moving slower that light in their pocket/hole through space.

[cryptonector]

SPOILER ALERT: Wormholes and warp drives will not work, cannot work, are not physically possible (even though they are "solutions" to the EFE), would not be feasible even if remotely physically possible.

[cryptonector]

Not really. But it does imply weird things. Sabine Hossenfelder did a video on this.

[analog31]

FTL means the bad guys have already reached you.

[King-Aaron]

There is also some folks that suggest that they are already here. Including an awful lot of high profile people within the defence sectors.

[cryptonector]

It means you see nothing interesting then a shockwave and here they are.

[analog31]

And here they were, because FTL travel implies eliminating the distinction between "before" and "after."

[cryptonector]

Not really: https://www.youtube.com/watch?v=9-jIplX6Wjw&pp=ygUKc2FiaW5lI...

[Teever]

That doesn't stop hypothetical automated sentinel probes that alien races have seeded the galaxy with as a surveillance net from picking up the atomic blasts and investigating.

[Yizahi]

To send and then slow a device of meaningful size across ten or hundreds of light years would require an enormous amount of energy, like truly incomprehensible amount. Then a civilization would need to produce them in millions and send to every single rock in the galaxy sector, because nuclear fission blasts are undetectable outside of star system. And then these robots need to function for billions of years continuously without any failure, because who knows which rock and at which time may develop sentient life. And when detection fission decay, such a robot must produce an enormous amount of power, to send a coherent optical signal over the tens of light years of distance. Meaning it has a gigantic power generator and equally impressive emitter. Which means even more mass has to be accelerated and then decelerated initially. And his sentient robot has to stare at a rock for billions of years without degrading electronically and without going insane.

And all that galaxy construction level effort for what? To learn hundreds or thousands of years late, that at rock number 123ABCD a fission has happened? And do what exactly with that useful information? Send extermination fleet? Or a robot with flowers, to pay respects?

People for some reason refuse to comprehend just how hard is it to send a speck of dust over light years of distance, let alone anything meaningful which won't break down in the process.

[cryptonector]

The reason to do this is not to prevent other civilizations from destroying themselves but to colonize the galaxy. It would still require all that you said (fantastical technology and enormous amounts of time) and then some.

And since the amount of time we're talking about is so large -- larger than the amount of time the beings that create these robotic probes can possibly continue to be alive -- that the only way it could work is if those beings accept robots as acceptable replacements for themselves, or if the probes carry embryos and can terraform planets and raise those embryos to adults and bootstrap a civilization.

Plenty of sci-fi has been written along these likes, like Ursula K Leguin's books, where human-ish beings on any given planet (e.g., Winter) turn out to be sent there from other planets to bootstrap a civilization and they have no memory of it. Or Pushing Ice, by Alastair Reynolds, where there is a robotic probe thing going on, but rather than continue the originating species [redacted to avoid spoilers].

[Yizahi]

We just went from absurdly insanely hard task, to a task I'd guess a thousand times harder. A communicator and observer probe is almost impossible enough, but to additionally preserve biological tissue for thousands of years in space is even harder than sending pure robot. And then terraforming part is just orders of magnitude harder than that. Communicator probe would be a few thousand tons maybe and packing maybe a few megawatts of onboard power. Lets be generous and give them a thousand times more - a few gigawatts, provided they are magic aliens and stuff. What can you terraform on a few gigawatts? Raise a temperature in a ten meter circle by one degree? Produce a few cubic meters of something from atmosphere? To terraform one would need a giant fleet of giant vessels, all fine tuned for some processes, and then they will work for millennia to change planet a tiny bit. We would notice that kind of operation in the Solar system.

I love LeGuin, Reynolds, and other, sci-fi is practically 90% of what I'm reading. But come on, the whole interstellar stuff is always predicated on very very optimistic assumptions and eventually magic.

[cryptonector]

Sure, ok, but what would a communicator probe accomplish? It could not communicate back to the origin -- the origin would be long gone. It could only communicate with the civilizations it finds, but to what end?

If any civilization were to build such a thing they would make it perpetuate themselves.

[sliken]

Only if you are in a hurry, say an advanced civilization has been around for 1M years (0.07% faster than us). It might well be worth sending out millions of drones to the most promising areas at 1% of the speed of light, their advanced sensors and telescopes and science would likely be able to pick the most likely stars based on metal content, vicinity (i.e. stable of 1B years), water, temp, etc.

Not to mention they could send probes closer and further from the galactic center to take advantage of the slower and faster rotation rate to see new stars.

As for the nuclear fission blast I have my doubts. Ham radio folks brag about 1000 miles a watt, in a lossy atmosphere and multiple bounces that reflect less than 1% for each bounce. Using advanced things like tubes of transistors and a copper cable thrown over a tree branch.

Using the 1 watt per 1000 miles the largest nuclear explosion would be 22 light years, and clear line of sight through space is going to transmit quite a bit better than bouncing off the atmosphere then off the ground several times.

An advanced civilization could make say a square km array (which us lowly humans have managed) and would understand nuclear bombs enough to know their likely signature, decay rate, shape of the curve, etc. Much like how astronomers use supernovas as standard candles for distance, despite crazy different red shifts.

Seems quite reasonable for a civilization to keep track of anything going on in their fraction of the galaxy.

"People for some reason refuse to comprehend just how hard is it to send a speck of dust over light years of distance" It's only hard if you are in a hurry, in fact we have 3 rocks come through our solar system from well more than a light year away.

[GloamingNiblets]

Isn't this ruling out outlier observations given our model, rather than evaluating our model given outlier observations?

[jansan]

Is Anyone here educated enough to tell if quantum entanglement could (hypothetically) be used to transmit information faster than light?

[rtkwe]

As far as anyone can tell you can't use it transmit information. Their states are mirrored but you can't modify the state of on of the pairs to change the state of the other, that just breaks the entanglement. So all you really have are two particles that happen to be in the same random state at any given time.

I don't think you can even tell given only one of the particles in a pair if it is still entangled so you couldn't even destructively send small amounts of information either. It's a neat work around for semihard scifi but the universe is stubbornly resistant to any pathways for anything including information travelling faster than the speed of light.

https://en.wikipedia.org/wiki/No-communication_theorem

[cryptonector]

Quantum entanglement cannot transmit information. Full stop. Let alone FTL.

When you measure an entangled particle that tells you, the observer, the corresponding characteristic of the other particle in the pair, but it will tell no one who has access to the other particle anything at all about what you wanted to say.

This is like transmitting information from you to you about a faraway thing (instantaneously! "FTL", but read on), but it's not useful because what you want to transmit information from you to someone else far away rather than from you to you.

[anomaloustho]

No, because you can only randomly measure the state of your particle and therefore the remote particle. (then lose the entanglement) But you can’t put the particle into a state.

[namanyayg]

All of human knowledge and observation so far points to the fact that we can't break the light barrier

[lawlessone]

my poor understanding of it is that it's like a split tally stick.

https://en.wikipedia.org/wiki/Tally_stick#Split_tally

So what if you put each half of split tally stick in a box hidden from view then move them a light year apart and then open your box? You immediately know what's on other stick but you can't change it anyway.

and also the act of viewing the stick destroys it.

[estimator7292]

That's our best guess anyway. My bet is that superluminal travel will be possible once we resolve quantum gravity and break all of Einstein's rules.

At least that's what I tell myself. Hard to appreciate the majesty of the universe if we're forever locked into a single star system.

[TrainedMonkey]

It would be really cool if that was true, but I would estimate the odds of quantum gravity enabling superluminal travel or comms as low. Occam's razor and all that.

[RajT88]

None of this is falsifiable. It requires understandings of physics we don't have, and we have no way of knowing which hare-brained theories today are correct and useful in the future.

That goes as well for how aliens light-years away can detect nuclear explosions and show up within days to check it out.

[itsanaccount]

"they" dont detect it light years away. from what has been published in the public domain, like in the congressional hearings, there are machines that have been here possibly a very long time. think at least 500 years. theres no indication the "they" behind those machines have ever made contact, or are on this planet, or are even still in existence. but there is something mechanical here that was not made by us.

as far as I know, the very few publicly identified records of speeds we have suggest a really big power source and the probable manipulation of fields we cannot yet (mass/gravity), but nothing breaking the speed of light.

so many people make leaps beyond the evidence we have and then declare them not plausible.

[RajT88]

Having read what's in the public domain from the hearings, I'm having trouble squaring these two things:

> there are machines that have been here possibly a very long time. think at least 500 years. theres no indication the "they" behind those machines have ever made contact, or are on this planet, or are even still in existence. but there is something mechanical here that was not made by us.

> so many people make leaps beyond the evidence we have and then declare them not plausible.

Why isn't the first one exactly what you're complaining about in the second statement? Have I missed something?

[cryptonector]

All the UFO talk is a distraction. You're welcome.