Will maintaining the network security always be profitable?

[anonppcoin]

Say the year is 2140 and miners are no longer receiving block rewards, only Tx fees. How do we know that these Tx fees will always make mining a profitable endeavor? Especially considering that block sizes are currently hard-coded and we don't know the impact of second-layer solutions?

Will something need to change in the meantime to guarantee this? For instance, a blocksize scaling mechanism that ensures that there is suitable demand for block space? Or will the users slowly take network security into their own hands and run distributed and/or embedded miners to decentralize the currency and not care whether or not the mining is profitable?

What happens if we develop a technology that provides everyone with unlimited free energy? Do we 'globalize' bitcoin?

It's questions like these that make me really trust the long-term prospects of PoS more than PoW, since we can continue to use self-interest and greed to improve the network indefinitely without needing to be cognizant of large-scale changes in how society functions.

Maybe this is more of a philosophical discussion.

[unamis76]

One can only speculate. I either hope that somehow mining will always be profitable or that the price of not having Bitcoin is way bigger than maintaining the blockchain at a cost.

Unlimited free energy is impossible. Energy will require resources to get in the foreseeable future.