3 ms·

We have no clue what is going to happen in billions of years. We are just extrapolating some known local parameters over a time span we can't directly observe.

dredmorbius 3y ago
A fundamental premise of physics and cosmology is that the universe is consistent. Unlike prescientific beliefs which held that the celestial sphere was comprised of some non-earthly material (in some conceptualisations, a quintessence or fifth element), what current astronomical observation, and both theoretical and applied physics show is that the laws and substance of the universe are consistent so far as we can observe. Well, aside from that pesky dark matter and dark energy stuff ... ... but the things we can see and detect ... show normal matter, mostly hydrogen, some helium, a bit of lithium, and a smattering of heavier elements in supernovae and neutron-star explosions, with gravity and light behaving as they do locally (again: relativistic effects notwithstanding). To argue that things we cannot observe might (or more strongly, do) behave differently ... is to argue on the basis of ignorance. That might be interesting, but it isn't scientific, in the sense of knowledge based on empirical observation and theory derived therefrom. Yes, at extreme extents, especially of time, things become uncertain. But we do the best we can. Over the past 150 years, human understanding of the greater universe has progressed profoundly. In the 1870s, the Earth and Sun were believed to be perhaps a few millions to hundreds of millions of years old, with extant theories failing to account for the observed energies of the overall system in a consistent way. The Universe was the Milky Way, other galaxies didn't exist. We've since determined the age of the Earth to within a few tens of millions of years, that there are galaxies beyond our own, and with present tools (including the James Webb Infrared Space Telescope) can look back to very nearly the practical limits of visual observation of the Universe. And we can see what stuff is made of, how fast it is moving relative to us, and how massive it is. The notion of truth values about future events has always confounded philosophy and epistemics. There is the problem of future contingents ("there will be a sea battle tomorrow"), or in the case of the cosmology of the far future, noncontingent futures (the ultimate outcome won't depend on our own actions), whose states we'll never be able to directly observe. The only guide we ultimately have is the presumption of consistency.
- im3w1l 3y ago
  Well nevermind the unknown unknowns. There are even known unknowns, like quantum gravity. Like yeah it's fun to speculate what will happen billions of years from now, but with many known gaps in physical theories, it's quite possible or even likely that our current prediction will have to undergo significant revision.
  - dredmorbius 3y ago
    True (a known known), but ... ... one of my broader and highly significant points reponding to treprinum is that models of the future beyond our ability to actually witness them are a fraught epistemic space. Of the various definitions of "science" is Popper's notion of falsifiability. There are numerous criticisms of that criterion, and the one I'm highlighting here is that we cannot falsify that which we will never witness. It's tough enough to make a prediction about the next five minutes, tomorrow, week, month, or year. The span of a human lifetime (or adult awareness) spans roughly 50--100 years. The span of a given civilisation or culture anywhere from roughly a century to a few millennia. Of civilisation, ten millennia, of modern humans, roughly 100--200 millennia, of humans as a species, about 2 million years. You and I will in all probability not be here to witness what will occur in the year 2123 (and quite probably much sooner, even given a long life). There are predictions which exist for what will transpire in that timespan, but our touchstone for judging these is largely based on what we have observed in the past, in various domains (astronomy, geology, climate, biology, ecology, social sciences, history, humanities). But in the sense that we can make and test a prediction ... we're sort of up a creek. I'll go out on a limb (and emphasize the point again) that consistency is our only guide.

dredmorbius 3y ago

A fundamental premise of physics and cosmology is that the universe is consistent. Unlike prescientific beliefs which held that the celestial sphere was comprised of some non-earthly material (in some conceptualisations, a quintessence or fifth element), what current astronomical observation, and both theoretical and applied physics show is that the laws and substance of the universe are consistent so far as we can observe. Well, aside from that pesky dark matter and dark energy stuff ... ... but the things we can see and detect ... show normal matter, mostly hydrogen, some helium, a bit of lithium, and a smattering of heavier elements in supernovae and neutron-star explosions, with gravity and light behaving as they do locally (again: relativistic effects notwithstanding). To argue that things we cannot observe might (or more strongly, do) behave differently ... is to argue on the basis of ignorance. That might be interesting, but it isn't scientific, in the sense of knowledge based on empirical observation and theory derived therefrom. Yes, at extreme extents, especially of time, things become uncertain. But we do the best we can. Over the past 150 years, human understanding of the greater universe has progressed profoundly. In the 1870s, the Earth and Sun were believed to be perhaps a few millions to hundreds of millions of years old, with extant theories failing to account for the observed energies of the overall system in a consistent way. The Universe was the Milky Way, other galaxies didn't exist. We've since determined the age of the Earth to within a few tens of millions of years, that there are galaxies beyond our own, and with present tools (including the James Webb Infrared Space Telescope) can look back to very nearly the practical limits of visual observation of the Universe. And we can see what stuff is made of, how fast it is moving relative to us, and how massive it is. The notion of truth values about future events has always confounded philosophy and epistemics. There is the problem of future contingents ("there will be a sea battle tomorrow"), or in the case of the cosmology of the far future, noncontingent futures (the ultimate outcome won't depend on our own actions), whose states we'll never be able to directly observe. The only guide we ultimately have is the presumption of consistency.

im3w1l 3y ago
Well nevermind the unknown unknowns. There are even known unknowns, like quantum gravity. Like yeah it's fun to speculate what will happen billions of years from now, but with many known gaps in physical theories, it's quite possible or even likely that our current prediction will have to undergo significant revision.
- dredmorbius 3y ago
  True (a known known), but ... ... one of my broader and highly significant points reponding to treprinum is that models of the future beyond our ability to actually witness them are a fraught epistemic space. Of the various definitions of "science" is Popper's notion of falsifiability. There are numerous criticisms of that criterion, and the one I'm highlighting here is that we cannot falsify that which we will never witness. It's tough enough to make a prediction about the next five minutes, tomorrow, week, month, or year. The span of a human lifetime (or adult awareness) spans roughly 50--100 years. The span of a given civilisation or culture anywhere from roughly a century to a few millennia. Of civilisation, ten millennia, of modern humans, roughly 100--200 millennia, of humans as a species, about 2 million years. You and I will in all probability not be here to witness what will occur in the year 2123 (and quite probably much sooner, even given a long life). There are predictions which exist for what will transpire in that timespan, but our touchstone for judging these is largely based on what we have observed in the past, in various domains (astronomy, geology, climate, biology, ecology, social sciences, history, humanities). But in the sense that we can make and test a prediction ... we're sort of up a creek. I'll go out on a limb (and emphasize the point again) that consistency is our only guide.