As long as BTC has a marketcap below that of gold, I think BTC is a buy, and here's a question

One of the chief issues about physical gold is the storage cost, an ongoing expense that never goes away.

But I just thought of another big problem: Repeated Authentication -- given that putting gold over a tungsten core is a known way to counterfeit gold bars (and also coins), a simple test of the surface of a bar is clearly insufficient to establish that a bar is legit.

The bar must be examined I would guess by drilling clean through, taking a "core sample" sort of. This process damages the bar (I do not know if bars are collectible like coins; I would guess that they are) which reduces the value and presumably costs money to do.

If you were buying multiple bars, I suppose you could sample them at random, but that is risky and would sellers accept this condition?

The above is pretty well known among people who buy physical gold, but the question that just occurred to me is this: Would not this testing have to occur each time physical gold changes hands? If so, what impact does this have on the value of gold if it is known that some percentage of the total value diminishes at each sale?

If a bar is sold multiple times, would that not mean that the bar by the final time is worth quite a bit less than the original bar? I honestly do not know the answer.

This concern is on top of all the other disadvantages of physical gold, the number one disadvantage simply being that attempting to move large amounts without others knowing is impossible. If you are trying to move your wealth out of a war zone, seems like having BTC is extremely superior to gold and in an emergency where you had to leave your country in, say, a day, I bet you would sell your gold at a very big discount to someone who had BTC to trade for it.