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Comment by dave_sullivan | Hacker News Reader

Couple points against humans physically exploring and colonizing space...

* Can't go faster than light (or even a large fraction of the limit)

* Cost. Look at price per compute vs price to bring something to space and tell me which trend seems more durable. Things will keep getting smaller while space exploration may not.

* Space sucks! Very inhospitable. I'd rather live in a biodome on a ravaged earth than mars.

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Alternative things to spend huge amounts of money on:

* LHC and other research on very small things

* More telescopes in space (light travels at the speed of light at least! Let it come to us instead of vice versa!)

* Encouraging trend of cheaper compute (not that it needs it)

* Brain to computer interfaces.

* Medicine

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What's to say some low mass x-ray binary systems aren't the final stage of life evolution? Super efficient harvesting of the sun and everyone living in a computer/black hole? Transcension hypothesis basically.

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* Can't go faster than light (or even a large fraction of the limit)

It's my weak understanding that because of time dilation & length contraction I could climb aboard a sufficiently powerful ship and travel 10,000 light years before dieing of old age. But, when I got there, I would find that 10,000+ years had passed at the destination while they waited for me. And, that if I made a return trip, Earth would be 20,000+ years older. But, importantly, /I/ would not necessarily be 20,000 years older.

So, the speed of light still sucks, but it mainly sucks if you care about returning home. If you give up on that goal, relativity does not say it's impossible to travel to arbitrarily far locations in human-scale timeframes.

Am I misunderstanding?

You're not missunderstanding. The problem is that to go that fast, even assuming perfect conversion of mass to energy with zero losses, you'd need to reach a speed of 0.999987 lighspeed. That gives a 200x time dilation factor so the 10,000 year journay appears to take you only 50 years.

You'd need to convert approximately 100,000x the mass of your capsule to energy to reach that kind of velocity, and the same again to slow back down at the other end. So for a one way trip, the payload would be on the order of 1/1,000,000,000,000th of the mass of the ship.

For comparrison, that means a starship the size of a Saturn V would be able to deliver a 3 milligram payload. If you assume even very slight efficiency losses, the possible payload size collapses quickly. Remember, some of that payload would need to be taken up by the propulsion system.

Not if you powered the ship with a laser from a solar system, or pick up fuel along the way.

The problem with beamed power over that kind of distance is beam divergeance (yes, even laser beams do diverge). Even very low wavelength beams, starting with very wide aperture emitters, end up with a beam many times the diameter of the solar system over these kinds of ranges. Good luck trying to capture that energy for your spaceship.

The problem with picking up reaction mass along the way is, you need to lose energy to accelerate it up to your own current speed first before you can consume it as reaction mass to speed yourself up. As you get closer to lightspeed, even with perfect, lossless conversion, e.g. at 0.9c you lose 90% of the energy of the reaction mass bringing it up to your own velocity and get only 10% of it for beneficial thrust. The total of required reaction mass, which was already ludicrously huge for any practical payload, balloons massively.

If you do actualy have energy conversion losses, those limit your maximum possible speed. If you lose e.g. 1% of the energy you convert, then once you're at 99% lightspeed, the energy you gain from burning the reaction mass is the same as the energy you expended bringing it upto your own velocity. So there's no net gain.

A top speed of 0.99C only gives you a time dilation factor of about x2.3 or so.

And of course all of that is assuming magic fantasy tech with unbelievably high efficiencies and negligibly sized engines and mass storage.

Ok, true about the divergence, but how installing lasers along your flight path? In principle that should work, right?

Or alternatively instead of placing stationary fuel pellets in your flight path, have them accelerated by an external accelerator to as high a speed as possible.

You'd end up spending hundreds of thousands of years, and expending the combined resources of many solar systems, just to deliver one guy in a space capsule. What is the point of this journey anyway?

I was thinking you were saying it was physically impossible. But you're right it's more of a cost issue.

The problem is still power though. The power requirements are too big to be anywhere near what's feasible for the foreseeable future.

So.. you're definitely missing a bit.

Light years is a measure of distance not time. As a result 10,000 light years measured from either parties perspective is 10,000 light years. ie a human on the ship would still experience 10,000 years of travel. No human can currently live that long.

Now change your hypothetical numbers to 10 light years and you're not misunderstanding anything. The human aboard the ship would have experienced 10 years of travel. However, any observer from Earth would have experienced 10*(some large factor) years, such that making a return trip "home" is impossible.

The flip side of time dilation is length contracation. If you are traveling at relativistic speeds, then space also contracts.

I think the issue is getting up to the speed of light.

Time would only slow seen from their perspective. You would still experience 10000 years of travel time.

There is no way to live longer by traveling fast.

Sorry, but that's wrong. The person in the ship would experience a shorter journey than would be measured by external observers.

http://en.wikipedia.org/wiki/Twin_paradox

> * Can't go faster than light (or even a large fraction of the limit)

That's a valid argument against traveling to other solar systems for sure. We could still travel to any planet/moon in our solar system in easily less than a generation and probably no more than 10 years.

> * Cost. Look at price per compute vs price to bring something to space and tell me which trend seems more durable. Things will keep getting smaller while space exploration may not.

Space will likely still be expensive for generations to come but reusability of rockets will decrease the expense of space travel by a couple of orders of magnitude. Imagine that we needed to build a new Airbus for each airplane trip, nobody would fly, it would be too expensive. Relative to rockets themselves, rocket fuel is cheap.

> * Space sucks! Very inhospitable. I'd rather live in a biodome on a ravaged earth than mars.

I don't know if I'd want to live my life on Mars either. That doesn't mean we shouldn't explore Mars and beyond.

>Very inhospitable.

I find it amusing that the space migration crowd is all into whiz-bang feel good tech like rockets, but not into the incredibly prosaic concept of terraforming. Where's the clamoring for more money spent there? Why aren't the sharp young minds migrating into that field? Why isn't anyone funding it? How many sharp young minds want to spend their life toiling on a project that won't finish until long after their great grandchildren are dead?

Its almost like the space migration crowd knows this is all a crock of shit. They just want rockets and other toys that have no where to go. Sure, we'll have an asteroid and possibly a Mars landing one day, but we can't stay. The same way we put men on the moon and had them drive around a bit, but at the end of the day, there was no reason to go back and certainly no possibility of staying.

I find it amusing that people speak of terraforming - making planets more habitable for humans - when making humans more durable is actually a lot more feasible by comparison, not to mention solves a lot of other problems at the same time.

A lot of hard problems in human space travel get much easier when you remove the constraint that human physiology must be immutable.

The point is the whole frame of the debate has changed. It used to be that exploring Mars would have required massive investment in single-use rockets for a vanity mission. Now we are on the cusp of realising an order of magnitude drop in the cost of access to space. Recovering F9 first stages is only phase 1. The next step would be a redesigned SpaceX rocket allowing for a recoverable 2nd stage as well.

It's no longer about massively costly media shows, but inexpensive, sustainable projects that may be achievable within our lifetime.

I disagree with your proposed alternate allocations.

LHC and other research on very small things

Has yet to provide actionable information, and could've been less of a boondoggle if the US had just funded their own damn apparatus years ago instead of killing the projecting.

More telescopes in space

Are basically pointless if you aren't intending to go anywhere.

Encouraging trend of cheaper compute

This is something that is getting increasingly hard to accomplish. We'd be better off spending that money rewriting existing utilities to be cleaner and less wasteful in their use of processing cycles.

Brain to computer interfaces

Very, very, very bad idea. Once this works, we've got a massive box of philosophical and psychological issues to deal with--reality becomes suspect and meaningless.

Medicine

Mostly worthless. We've got the technology to save lives and solve health issues, but either politics or capitalism work directly against it. As long as there's a buck to be made convincing people to be unhealthy, we lose.

Even with better medicine, what do we do with all the extra people? Where do they go, since we're not going to space?

> reality becomes suspect and meaningless

If you're going to get that hung up on philosophy, reality is already suspect and meaningless. This observation dates back at least to Descartes. His solution involved the ontological argument for the existence of God. My solution is to not get that hung up on philosophy. Take your pick.

> Brain to computer interfaces

> Very, very, very bad idea. Once this works, we've got a massive box of philosophical and psychological issues to deal with--reality becomes suspect and meaningless.

Objective reality is suspect anyway, since all the methods of accessing it are subjective.

Brain to computer interfaces may draw more visibility to this long-known philosophical problem, but it doesn't fundamentally change the landscape.

>Brain to computer interfaces

Very, very, very bad idea. Once this works, we've got a massive box of philosophical and psychological issues to deal with--reality becomes suspect and meaningless.

Sure, there are all sorts of bizarre risks inherent in this, but is there any possibility that this won't happen? It seems all the trends point this way?

Surely, Snowden's revelation point to much darker trends.

I don't think we really disagree, but what do you mean, specifically? I foresee the eager adoption of brain-computer interfaces by significant portions of the population (possibly including myself), and all sorts of problems ensuing from that. I think those problems might well include evil shit devised by our various enforcement agencies, and I won't be surprised if Snowden's whistleblowing successors reveal just that.

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