I suspect that the question about the price discovery mechanism of gas/Ether was not studied very deeply by the Ethereum developers.
The mechanism that currently exists must work by miners adaptively changing the lower bound of Ether per gas (asking price), and creators of transactions - offering certain prices and watching if the transactions get mined.
Number 0.05e12 wei, or its order of magnitude, most probably came out these sort of calculations: we have 5 ether per block mining reward, or 5e18 wei. One transaction costs at least 21000 gas. If every miner, after receiving the reward, spent all the ether on sending transaction, how many should they be able to send per second? If we allow around 3000 per second, then we can arrive at the right order magnitude for the current gas price.
Let me now make a little diversion.
Since miners do not current have a way to advertise what their current asking prices are, the transaction creators are effectively making 'blind' bids in hope that they will be equal or higher than the asking price (but not much higher). Also, the miner do not have a way of explicitly rejecting the bids when they are too low. So the bidders have to assume rejections implicitly, seeing that their transaction did not make it into the next block. That, of course, does not mean that all miners would reject the bid, only the one that happened to mine that block.
From above it should be obvious, that the current state of the gas price discovery is very inconvenient and inefficient. Therefore, some explicit market mechanisms would need to be added either to the protocol, or in a form of contract. This is probably easier to do post Proof-Of-Stake, because offer prices can be signed and relayed as ordinary transactions. But even now it would be possible to create such a contract, 'gas market' :)
There is no fixed gas price that transactions must have.
You can specify the gas price, and if you set a gas price within certain bounds, the transaction will be accepted by miners using their default values and oracle.
The default gas price is now 0.02 microether which is equivalent to:
- 0.00000002 Ether (.02 * 1e-6)
- 0.02e12 wei
- 20000000000 wei
- 20e9 wei
- 20 Gwei (gigawei)
- 0.02 szabo
When you send ETH, your client (Geth or Parity) will use the default gas price of 0.02 microether.
If 1 ETH is $10, 1 gas will cost 0.00000002 * 10 dollars.
If ETH is $10, 21000 gas will cost 0.00000002 * 10 * 21000 = 0.0042 dollars, which is 0.42 cents.
If ETH is $1000, 21000 gas will cost 0.00000002 * 1000 * 21000 = 0.42 dollars, which is 42 cents.
Best Answer
Yes, you can. But miners have a default strategy for determining gas price to charge and if the amount you're willing to pay is below that, your transaction will be rejected. (Try setting the slider all the way to the left in Mist and try to send a transaction.)
Completely arbitrary and made up by the gas price oracle running on miners. There is no necessity to use this oracle, you could swap it out for a really greedy or really kind one. It probably helps the stability of the network to leave things as is though.
Realistic would be assuming most people don't mess with the gas price oracle settings when they mine and they use all defaults. Which means as you fill up more and more of the 3,141,592 maximum gas in the block, you'll need to provide a higher and higher gas price. (Which by default discourages overusing gas / filling blocks.) Too low = your transaction won't go through. Too high = miners will probably thank you. (There is no too high with gas prices.)