Recent comments in /f/askscience

GeriatricHydralisk t1_jct5ayu wrote

Reply to comment by [deleted] in How different were the first horses domesticated by humans compared to modern horses? by clacker96

False, horses evolved in the Americas first, and precursor species as well as modern horses repeatedly migrated across the land bridge to Eurasia.

Then, about 12,000 years ago, they all died out in America, a long with all the other native Megafauna, right around the time a certain species with tools, fire, and a reputation to eating things into extinction showed up.

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mesouschrist t1_jct3knw wrote

Reply to comment by fr293 in We're often taught that objects travel to lower energy states to reach stability. But the energy of the universe is constant - doesn't that just mean other surrounding things go to higher energy states? What decides which thing gets to have low energy? by SMM-123Sam

The energy of the universe is constant under the assumption that there are laws of physics that apply to the universe across all times (i.e. the motion of things in the universe can be explained without an explicit time dependence, like the gravitational constant shrinking with time without any underlying reason). Energy is the conserved quantity associated with time invariant laws of physics. So if you think energy is decreasing or increasing, you just have the wrong definition of energy (like when a ball rolling across the table slows down, it's lost energy, but really the energy has gone somewhere else).

It doesn't matter whether or not the system is relativistic - certainly energy is still conserved in special and general relativity. But I'd be curious if you could elaborate on what you were thinking there.

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mfb- t1_jcsg4pp wrote

Reply to comment by spiteful_rr_dm_TA in What is the ultimate fate of rocky bodies? by spiteful_rr_dm_TA

It's hard to imagine a scenario where protons are absolutely stable. If there is no other process then gravity should be able to make them decay via virtual black holes. But assuming they are absolutely stable you expect the nuclei fuse/split to form iron and nickel over time and stay like that forever.

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