Um, in order to deplete metal, you would have to of had chemical changes to all metals in the galaxy so that they are no longer metals... this is by far the most stupid threads ever, any of you that has taken chem of any level know that there are such things as "physical" change and "chemical" change, ones that are reversible and one that is not. I am sure aliens wouldn't be stupid enough to burn precious metals like oil and gas.
A far more realistic feature of depletion is the opposite.... space pollution etc. from battles, star bases or whatever you can come up with. The only solution would be to send ships to collect all the wasted scraps and recycle them.
I also ridicule this idea because fusion allows for smaller atoms to be come bigger atoms, so I am sure that you can turn anything into gold if you really wanted to, besides By the time they exhaust all non renewable resources in the galaxy the humans would probably have destroyed the galaxy already...
I agree with most of this thread, but the bolded part.
Why is that? Theoretically, you could turn hydrogen into any element. Any element. Now, of course, turning into iron or anything heavier would be a loss, but everything from hydrogen to iron would by an energy gain. And of course the net effect of even turning hydrogen into say, gold as you say would be a net gain. Granted the steps from iron to gold would be a loss, but it's still possible. And there is a A LOT of hydrogen in this universe.
Uhh, but that doesn't mean the the source from which the ore was derived wouldn't be depleted. Mines are played out all the time on this planet because the ore runs out. The metal's still there, but the source is long gone. Think a bit before you call someone's thread "stupid."
We're not running out of hydrogen any time soon. Nuclear fusion is possible until then.
A lot of the commenters here clearly dont understand issues like EROEI and depletion rates. You dont have to 'run' out of physical ore or energy source or whatever your extracting for it to become uneconomical to continue extraction efforts.
Since there is clearly a lack of understanding of the basics here. Humans, and (aliens) always go after the 'low-hanging' fruit first. The easiest (cheapest) and highest-quality reserves will be exploited first.
That would be on planets with breathable atmospheres.
Next to go, would be marginal planets with poor atmospheres, moons, high gravity whatever.
After that-closest metal rich asteroids
Then-you go for most distant and miserable asteroids and hunks of rock in your solar system.
You are thinking in terms of a pre-fusion civilization. Nuclear fusion changes everything. Hydrogen could be turned into anything. Anything.
The concept of an EROEI by the way is something I do understand. The amount of energy invested versus that returned. An example would be our oil extraction. First we go for the easiest, then the ones that get progressively harder (witness the BP oil spill a couple of years ago - they're getting oil from deep out to sea), and finally, the hardest, which would be the tar sands (and perhaps someday converting coal to oil). And of course, as we transition from large easily extracted reserves of light sweet to tar sands, our EROEI declines.
But what does any of this have to do with resource depletion? Habitable space depletion, yes, but not resources.