This article is quite old now, but still worth replying to, I guess, with some new information.
The question of what is backing Bitcoin has a very simple answer, but with some huge consequences on the conventional mindset.
The sun, is what is backing Bitcoin.
We know now that the majority of power used to create Bitcoin is solar.
That, is the only source which is unlimited, and free after installation, thus guaranteed, to produce Bitcoins at profit, no matter the difficulty and energy of production.
We know also that the total amount of solar devoted to Bitcoin is capable of powering a medium sized country (or several smaller ones).
What this means is that Bitcoin is actually generated from free power.
Therefore Bitcoin itself is free.
And yet it is backed by something with more authority than any bank, the sun, the energy from which created everything we know, for free, and continues to do so, every day.
And the sums of fiat exchanged for Bitcoin continue to increase, hand-in-hand with the difficulty of computation, and therefore also the amount of work / energy needed to create each Bitcoin.
Bitcoin is literally money-as-sunlight.
The consequences, squared
For all known history, until Bitcoin, the economy, and thus the world money supply, was considered like a closed box of assets; something to be quantified by a fixed amount of gold, or other fixed asset.
So the ideas of dilution of capital, kind of worked.
Scarcity was enforceable.
Therefore profit kind of worked.
All things could be witheld until appropriate payment, or promise of payment (thus enslaving the promiser), was made.
As long as we lived only from the energy of the planet, and one another (labor), the zero-sum game of total scarcity-until-payment could be played.
And it was, at huge cost to our species, and our environment.
Now, with free solar energy being encoded directly from the sun, and added to the world economy, by being exchanged for fiat monies of all denominations, a free money-fall is appearing, like a waterfall, which is being added to our world economy, funded by the extraterrestrial donor of all things, the sun.
Now, free money really does have value.
So there is no longer any possibility of dilution of capital.
Now, when scarcity is enforced, the enforcing “Authority” experiences a reduction of value.
Witholding, results in the denomination being witheld, reducing in value.
Thus capital, retained in expectation of attracting interest, does the exact opposite, it loses value.
When massive stimulus is issued, the value of the currency donated goes up, not down.
Capitalism, is no longer possible.
However, generation of massive wealth, by giving away money is becoming possible.
After all, what else is one doing, when one exchanges a large sum of hard-earned conventional money, for money encoded from something which was absolutely free.
So now it is only a matter of time, until solar energy collection is scaled to something capable of supplying the energy needs of all humanity, and the final Bitcoin is minted, and the money-fall of free, infinite wealth is freely available to all people.
The sun has unlimited free energy.
At last we are seeing how to make use of it in our economy.
Infinity divided by many billions of people is still infinity.