Space, the Final Frontier: It Gazed Into My Open Refractor

The Something Awful Forums > Discussion > Debate & Discussion > Space, the Final Frontier: It Gazed Into My Open Refractor

Haystack: Jan 23, 2005

Every single alien civilization has lived and died in its own home system. Even if FTL travel were possible (which it almost certainly is not), the resource costs of operating in space are too high. Gravity wells are a bitch, to say nothing of the radiation.

Haystack fucked around with this message at 17:22 on Nov 29, 2018

# ¿ Nov 29, 2018 17:19

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# ¿ May 11, 2024 19:29

Haystack: Jan 23, 2005

axeil posted:

What about von Neumann probes?

https://en.wikipedia.org/wiki/Self-replicating_spacecraft#Von_Neumann_probes

Why don't we see them? You'd only need 1 civilization around our tech level in the galaxy to decide to make them for us to likely see evidence of their existence.

They also have to pay the costs of operating in space. Robots are as susceptible to radiation and general entropy as anything else.

# ¿ Nov 29, 2018 19:48

Haystack: Jan 23, 2005

Aliens don't have interstellar civilizations for exactly the same reason humans never will: it costs way, way, waaaay too much energy, and is way too slow. A physicist on another forum I frequent broke it down like this:

quote:

Everyone thinks that space is big, but they're wrong. It isn't big, it's big. People don't comprehend the scale. When I hear people talking about 'fast space travel' I start to itch a little bit. People that say that sort of thing don't mean 'fast' in the sense of being able to send a tiny unmanned probe to the nearest exoplanet in 'only' a few million years, they mean being able to hop a space-bus and have a family vacation in Betelgeuse. And that isn't going to happen, not ever. I don't care what kind of weird future technology and vast oceans of clean cheap energy you postulate. We are stuck on Sol forever, and let me show you why.

The closest terrestrial planet we know of is Gliese 876 d, which is 15 light years away. Sure, the atmosphere is well above boiling, but we are not very picky space travelers. Let's say that we have perfect technology. Our engines are 100% efficient, fuel weighs nothing, and accelerations are instantaneous. This is the thermodynamic limit. It cannot get better than this. What would it cost us to send someone or something to Gliese?

Here's a table. I have listed the energy cost of the voyage in units that I call 'Globes.' Globes are the percentage of the entire world's energy production per year. I chose three different masses for your edification. Use the globes per kilogram if you want to quickly calculate the cost of sending your favorite sci-fi starship on a 15 light-year journey at the speed of your choice. Use the 1,000 kilogram table if you want to launch your Honda Civic into space. Use the 500,000 kilogram table if you want to use the International Space Station as your ship (which by the way, is terribly cramped and unpleasant).
pre:
+--------------------------------------------------------------------------------------------------------------------------+
|Velocity (c)|Time, Earth's Frame (years)|Time, Ship's Frame (years)|Globes per kg|Globes per 1000 kg|Globes per 500,000 kg|
+--------------------------------------------------------------------------------------------------------------------------+
|0.01        |1500                       |1499.92                   |0.0000000095 |0.0000095         |0.0047               |
|0.1         |150                        |149.25                    |0.00000096   |0.00096           |0.48                 |
|0.2         |75                         |73.48                     |0.00000392   |0.00392           |1.96                 |
|0.3         |50                         |47.7                      |0.00000917   |0.00917           |4.58                 |
|0.4         |37.5                       |34.37                     |0.000017     |0.017             |8.65                 |
|0.5         |30                         |25.98                     |0.000029     |0.029             |14.69                |
|0.6         |25                         |20                        |0.000047     |0.047             |23.73                |
|0.7         |21.43                      |15.3                      |0.000076     |0.076             |38.00                |
|0.8         |18.75                      |11.25                     |0.000127     |0.13              |63.29                |
|0.9         |16.67                      |7.26                      |0.00025      |0.25              |122.86               |
|0.99        |15.15                      |2.14                      |0.0012       |1.2               |578.05               |
|0.999       |15.02                      |0.67                      |0.0041       |4.1               |2028.44              |
|0.9999      |15                         |0.21                      |0.0132       |13.2              |6618.27              |
+--------------------------------------------------------------------------------------------------------------------------+
There's a lot I want to unpack here.

Generous Assumptions

I can't emphasize enough how nice I'm being here. I'm granting instantaneous acceleration, which is huge. If you have to actually worry about thrust, the times become much, much longer, while still requiring the same amount of energy. I am also granting zero weight fuel, which is nuts. On top of that, we have perfect efficiency. We lose nothing by charging the engines nor by firing them (In contrast, we lose about 60-70% of the energy generated from burning coal by the time it reaches our homes). These numbers are also for fly-by arrivals. If you want to actually stop when you get there, then double the energy cost.

Scale: Earth Time

This is the only part of the chart that scales in a simple, intuitive manner. If you double your ship's speed, the guys on the ground have to wait half as long for it to get there. Nice and simple.

Scale: Ship Time

For the ship, things are a bit weirder. As velocity increases, relativity becomes impossible to ignore. At 0.8c, it actually takes the ship less than 15 years to travel a 15 light-year distance. This might sound like FTL travel, but it's really nothing of the sort. Space is contracting for the ship. The distance between objects is shrinking. The 0.99c ship gets to Gliese in 2.14 years because in its frame, Sol and Gliese are only about 2.14 light-years apart.

Notice that the scaling becomes extremely non-linear towards the end. Increasing your velocity from .9c to .99c is only a 10% boost, but it cuts the travel time (for the ship) by about 70%. Welcome to space-time, you fuckers.

This also causes out-of-synch issues with your earth buddies. I was going to get into the heartbreaking consequences of this, but I'm not going to bother because the next section is going to render that moot.

Scale: Energy

And now we come to my point. Classically, energy scales by the square of the speed. So doubling your velocity doesn't double your energy cost, it quadruples it. That would be bad enough, but then relativity adds in an asymptotic scaling factor that goes berzerk as you start to approach c. Just look at those numbers. Really, look at them.

I chuckle a bit when I hear about space tourism. We aren't going to other planets. Not ever. The cost of sending even a small ship to our closest (and totally uninhabitable) terrestrial neighbor and having it get there before the crew dies of old age has to be measured in multiples of the earth's annual energy output. I don't care what kind of future tech that we have. How much more energy are we gong to be producing with our tri-lithium anti-phasing widgets? A hundred times as much? A thousand? Those both sound like wildly unrealistic numbers, and they both totally don't solve the problem. If you have to deal with issues like real acceleration, real efficiencies, and real fuels, then a million-fold increase probably wouldn't rescue the project.

We're not claiming other planets. We only have the one that we're on. We need to take care of it.

# ¿ Nov 30, 2018 02:21

Haystack: Jan 23, 2005

twodot posted:

Sending a human between the stars requires new physics, building a von Neumann machine that goes off and eats Jupiter to build a starship that cruises at a small percentage of lightspeed is incredibly difficult, pointless, time consuming, and offensive to amateur astronomers, but it doesn't need any physics breakthroughs.

Eh... the energetics are better, but the timescale is a huge problem. You're talking about a process that has to keep working towards a goal for tens of thousands of years per generation in unimaginably harsh conditions with zero room for error. Entropy is not a kind mistress.

# ¿ Nov 30, 2018 03:16

Haystack: Jan 23, 2005

I mean, pretty much everything is in one big gravity well or another. Even if you're not fighting to get off a planet, you're paying fuel and/or time costs to fight orbital sync issues.

# ¿ Dec 9, 2018 05:10

Haystack: Jan 23, 2005

Ita likey he was talking the problem of cosmic radiation being a severe health and maintenance hazard.

# ¿ Aug 29, 2021 17:37

Haystack: Jan 23, 2005

I AM GRANDO posted:

I don’t know—space is so utterly empty. I’m putting my money on there being some fundamental aspect of the nature of the universe that we haven’t hit upon yet and can’t guess about that has something to do with the probability of detectable civilizations arising in the Milky Way. It’s a little disturbing that we don’t even have ambiguous evidence to argue about. That usually means there’s something key that we’re not getting.

Certainly, I don’t think that we as a species are particularly suited to maintaining the planetary conditions that allowed us to create global civilization. Global warming might not keep us from going to space, but the bad habits that caused global warming aren’t really slowing down.

I mean, it's not a huge mystery: space is too big. Subluminal space travel is too slow and expensive to be practical, and FTL is impossible*. Hell, even radio signals can only go so far before they attenuate to nothing. Every island of life is just too damned far apart.

*Short of general relativity being really, really wrong in basic, unexpected ways.

# ¿ Apr 11, 2023 23:36

Haystack: Jan 23, 2005

I AM GRANDO posted:

There’s definitely something atypical about the rate of technological development we’re currently living through vs the last 300,000 years. I can’t imagine it’s possible to just keep going at the same pace for the next 100,000 or even 10,000 years. We’re either careening toward extinction or collapse into a pre-tech species or going to reach some kind of plateau, whether because innovation delivers some kind of optimum solution or because we run out of something we need as we make due.

Finding another civilization would tell us a lot about the boundaries between life, civilization, and technology and how we might best understand them as related or distinct from each other. I have to admit that I have a hard time imagining the human species has much of a future on a geologic time scale given what we’ve been up to in the last 10,000 years.

What helped me was getting it in my head that science is a process of discovery, rather than a process of creation. It sounds a bit obvious to say, but science is very sharply limited to only finding out things that actually exist. There are plenty of creative processes in the world that science can study (evolution, geology, etc), but the laws of physics are notable for being more or less immutable. There is never going to be a discovery that broadly violates the observations that underpin relativity or quantum mechanics, any more that we could discover that South America never existed.

Many, if not most, people seem to be in the mindset that science is some sort of unbounded, exponential process that will continue on the way it did the last 100 years, but I think they're deluding themselves. Science will always have a place, refining itself and studying aforementioned creative processes, but I think we've more or less got the basics down.

And the basics paint an utterly dismal picture of interstellar travel.

# ¿ Apr 12, 2023 12:34

Haystack: Jan 23, 2005

Personally, I think of interstellar travel as an entropy problem. You're trying to get a very specific result over a very long time period while expending collosal amounts of free energy in a hostile environment that is simultaneously perfectly insulated, immensely cold, and constantly irradiated.

# ¿ Apr 14, 2023 12:37

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# ¿ May 11, 2024 19:29

Haystack: Jan 23, 2005

Aurora is a pretty good hard sci-fi book that delves into a lot about the self-sustainability of a generation ship. It's also, coincidentally, very depressing!

# ¿ Apr 14, 2023 17:07

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