[felixchan]

>And then I better understood the stupendous energy requirements for a two-way trip to even the very closest neighboring solar system. And it is just not practical, even for a civilization at the end of the technology development tree.

This is blind arrogance.

[ansible]

Eh, no it isn't arrogance. It is math and physics.

Have a look at a few links. So first off, chemical propulsion is right out:

https://blogs.scientificamerican.com/life-unbounded/why-chem...

You really need something like anti-matter:

https://en.wikipedia.org/wiki/Interstellar_travel

You're still looking at hundreds of years or more for a nearby two-way trip.

It is far more practical to send out probes one-way (which is quite slow), and then build the infrastructure at the destination to receive transmitted mind-states.

The initial probes take a long time to reach their destinations, because they have to have means to deaccelerate. The faster you accelerate, the more mass you have to carry with you to deaccelerate.

[eloff]

It's our current understanding of physics. Those limitations might be impassable. Or it might be possible that there is a higher physics where things like the speed of light are bypassed. Like discovering that quantum entanglement is based on some mechanism that can be manipulated to communicate faster than light, or one can skip over distances through higher dimensions, or we decode the source code of the automata that creates the universe and it's immediately replaced by one even more bizarre. There are some theories that this has already happened :)

The point is it's arrogant to say what's impossible for all time, because nearly everything we do today was impossible a short thousand years ago.

[jerf]

I think it's important to break the conversation clearly into two parts: Here's what could be true about aliens if we're largely correct about physics, and here's what could be true ignoring that constraint.

The problem is people want to have really muddled conversations about that. The people having the second kind of conversation yelling at the people having the first kind of conversation is probably the most frustrating element of all, especially when they strike a morally superior pose which is, IMHO, entirely unjustified.

If you want to ignore all current science and astrophysics when you discuss aliens... fine. Be my guest. No sarcasm. I have some beliefs on that front myself. BUT... you need to be aware that you're basically engaging in groundless speculation, and in particular, you have no grounds to be yelling at people about their groundless speculation.

We can have a much more grounded discussion about what aliens could look like if we are largely correct about science. And there's no need to accuse people about being "arrogant" if they choose to have that discussion, because frankly, of the two, it's the more interesting one. The "well, what if we're wrong about everything?" may seem like fun for a moment, but there's no there there, really. What if we're wrong about everything? Well, what if we are? What if we're all just in an ancestor simulation... but the descendants running it are super-advanced honey bees running their ancestors and we just happen to be around? Well... what if? There's nowhere to go, or if you prefer, there's nowhere you can't go, which is actually the exact same thing.

On the other hand, if we stick to biology and cosmology and relativity and science in general, we can have all sorts of interesting discussions. What about that result on Venus? That's a question rich enough to build a concrete career on. What would aliens look like in our real universe? How much more advanced could they be? Would they, in fact, build rather human-sized spaceships that are apparently capable of crossing the interstellar void, but not flying around in our atmosphere without crashing into things? Would they in fact need to keep kidnapping humans over and over for decades on end? Sensible discussions can be had on these matters if we start from a concrete base. The whole "But what if we're, like, wrong about everything and we're, like, actually soap bubbles floating in the wind?" discussion has nowhere interesting to go, because it creates just one big undifferentiated and indistiguishable mismash of what ifs.

[eloff]

You're probably not addressing me specifically, but there is no yelling in my comment.

I do think we have to ground any interesting discussion by what is possible within the limits of science. Otherwise we're just talking fantasy.

For the most part, I do not think we should discuss the limits of engineering, that is what's practical or not, because we're nobody to say what is practical to a type II or type III civilization.

My dad's astronomy professor told the class it's impossible by the laws of physics to create a telescope that can see exoplanets. He went through the equations to show you could never build a telescope mirror to accomplish that. What he didn't think of is we found other ways to create bigger telescopes and we used gravitational lensing to zoom in on a distant star. Nothing in our understanding of physics changed to allow that, merely a change in how we looked at the problem. That's why it's so arrogant. We don't know everything about what is possible or not, and one day we might just see a way around limitations that seem absolute today. Our short history is filled with us doing that again and again.

[jerf]

"You're probably not addressing me specifically, but there is no yelling in my comment."

Yes, my apologies for the implication. I deliberately wanted to pick a more sensible comment to post under.

"For the most part, I do not think we should discuss the limits of engineering, that is what's practical or not, because we're nobody to say what is practical to a type II or type III civilization."

There's two aspects to engineering we can talk about; fundamental limits, and whether we can attain those fundamental limits.

If you look up the concept of computronium, you'll find a discussion of the fundamental limits of data storage in our universe, for instance. Proposing an alien civilization that exceeds those is stepping into fantasy. We can sensibly discuss what just isn't possible.

On the other hand, given that the "fundamental limit" is "the number of bits you can encode on the event horizon of a black hole", it's at least plausible to consider that no possible engineering project could ever create such a storage device. It's hard to talk about the "what is possible" side.

[eloff]

Yes, I agree. We're probably not going to exceed fundamental limits.

However, some number of fundamental limits might turn out not to be fundamental or there might be a way around rather than through them. We can't be 100% sure of what's impossible, but it is stepping into the realm of the extremely unlikely, at least from our current understanding of the universe.

[ansible]

> The point is it's arrogant to say what's impossible for all time, because nearly everything we do today was impossible a short thousand years ago.

I never said impossible, I said impractical.

If you are content with really long travel times (thousands or tens of thousands of years one-way), then of course you can travel to other stars.

By the time such means are available, I doubt that entities will bother with shipping matter two ways over such distances.

Also, if you're talking about an uploaded or otherwise synthetic consciousness, that entity may be experiencing time a 100x or more faster than a baseline human does now. So a then thousand year trip would seem like a million years. That's a long time to stay away.

[eloff]

That seems likely from our perspective, but it's pretty arrogant to think we understand the limitations and desires of civilizations millions or even billions of years ahead of us.

Certainly we would have failed at that task of predicting our own limits and desires just hundreds of years ago, nevermind an alien race.

[felixchan]

It's arrogance because you think that your current system of science is relevant. Civilization has been around for only 5000 years.

How do you know other planets do not have elements that have anti-matter properties?

[ansible]

> It's arrogance because you think that your current system of science is relevant. Civilization has been around for only 5000 years.

So, if magic exists, there also might be aliens. Got it.

> How do you know other planets do not have elements that have anti-matter properties?

Well, we haven't observed anything that gives even a hint that something like that exists.

The matter / antimatter disparity is still quite a mystery. But we don't see any evidence of antimatter out there in any significant quantities. So if aliens want to use it, they have to make it the hard way, just like we do.

Beyond current state-of-the-art technology would make manufacturing and containment of antimatter easier, but even then it is a long way from practical.

[felixchan]

Sounds like you sure know how aliens make things.

[ansible]

And it sounds like you are sure the laws of physics don't apply to aliens.

Extraordinary claims require extraordinary evidence.

[davidivadavid]

The whole point is that we don't know what the laws of physics are.

[postalrat]

You've already proven when present with extraordinary evidence your reply will remain "Extraordinary claims require extraordinary evidence."

[maxharris]

Even Isaac Arthur did a video on the Navy's videos, and he's more open to this than you. Please give this a rest -