Science philosophy in the NY Times

[steuard]

Brian Greene wrote a NY Times op-ed about the implications of the accelerating expansion of the universe. As he says,

Because of this, when future astronomers look to the sky, they will no longer witness the past. The past will have drifted beyond the cliffs of space. Observations will reveal nothing but an endless stretch of inky black stillness.

If astronomers in the far future have records handed down from our era, attesting to an expanding cosmos filled with galaxies, they will face a peculiar choice: Should they believe “primitive” knowledge that speaks of a cosmos very much at odds with what anyone has seen for billions and billions of years? Or should they focus on their own observations and valiantly seek explanations for an island universe containing a small cluster of galaxies floating within an unchanging sea of darkness — a conception of the cosmos that we know definitively to be wrong?

I'd thought before of the implications for scientists from future races that never had the chance to see other galaxies at all. Before reading this I'd always just assumed that we humans would be okay (assuming we survived that long) because we'd been lucky enough to see the truth. But now I worry that he has a point: assuming we survive that long, how much will those future scientists really trust our observations, so at odds with what they can see for themselves?

That's related to one of the philosophical realizations I've had about studying things like string theory and cosmology: Some true things are simply impossible for us to observe or measure, and many more are just not the sort of thing one can predict. It's hard to be comfortable with that: I'd like to imagine that I live in a universe that's not just understandable but verifiably so, but there is no guarantee that our universe will cooperate with that desire. The thought that it might cooperate for a while and then stop is especially uncomfortable: what might we miss if we don't develop the technology to observe it fast enough?

Comments

[nasu-dengaku.livejournal.com]

Quick thought -- it seems like this is the sort of issue historians deal with all the time. It's a hell of a lot easier to determine truths of the Battle of Gettysburg if everyone can observe it happening. However, we only have primitive accounts of the event by people who were busy commanding armies and/or being shot at. It would be a lot easier for historians if they could re-run the Battle of Gettysburg over and over in a lab, but they can't.

As for missing technology to observe things, I think cosmology is moving so slowly that we'll be either all dead or a galaxy-spanning intelligence by the time any of these issues come around.

What isn't changing slowly, however, is our civilization, and the transitions that will take place over the next 100 years or so should be unprecedented. There's probably a lot we can learn about emergent order in complex systems and numerous other things that we're just not observing right now, and will never get to observe.

[steuard.livejournal.com]

Well, yes, the time scales of cosmology are a wee bit slow: the issues here aren't all that likely to be relevant for any given civilization. But I agree that similar sorts of phenomena may show up in other areas of human knowledge.

As for historians, I'm probably just a snobbish physicist. I've always taken comfort in not needing to trust the ancients on anything, knowing that I can always just check their claims myself if necessary. It's startling to think that my field isn't as immune to that as I thought.

[robbbbbb.livejournal.com]

"It would be a lot easier for historians if they could re-run the Battle of Gettysburg over and over in a lab, but they can't."

Who says?

(I kid, I kid.)

[steuard.livejournal.com]

Hey, we've got a copy of that! Never played it, though: a bit in-depth for our usual gaming groups. How is it?

[robbbbbb.livejournal.com]

I haven't played it, either. I'm not a Civil War guy; more WWII.

As an older AH title, I suspect it's decent, but it has holes. The older AH games were a great foundation for the wargaming hobby, but the state of the art has proceeded apace.

[jon-leonard.livejournal.com]

I was under the impression that the it was more that remote galaxies would redshift toward invisibility rather than simply leaving us with a black sky. Not that (given enough time) it makes that much of a difference.

I'm less troubled by the implications for future scientists, though. It's not too much of a stretch to assume such scientists can figure out that there's a cosmological constant, and ponder what the consequences might be like if the universe had once been much more compact. If they have historical records, that makes it that much more plausible.

To make an analogy, we have some pretty good estimates for how much the earth's rotation is slowing, but the best of those is due to a historical record. Some ancient Greek was born on the day of a solar eclipse, but the location doesn't match where a straightforward model says the eclipse would have been. So the updated model includes the Earth losing 30 degrees of rotation over a few thousand years.

A lack of good independent observations does slow down our understanding of cosmology. The problem may still be tractable even so.

[steuard.livejournal.com]

No, it really is honestly a black sky (outside of our galaxy), which I find at least mildly terrifying. The accelerating expansion of space will (according to current theory, which may of course be wrong) become increasingly rapid until "new space is being created" between galaxy clusters faster than light itself can cross that space. So not only would the distant photons be extremely redshifted, but they'd also become increasingly rare (as only the ones that were right "on the edge" of making it to us would keep trickling in).

Good point about historical records, though. Especially if we manage to come up with some fundamental theory (with locally testable predictions) that implies a value for the cosmological constant, that would give future scientists a reason to believe our crazy stories about countless distant galaxies. (I hope those future scientists aren't as dependent on data from the CMB for progress as we're likely to be, though!)

[kirin]

It occurs to me that what this phenomenon really gives a deadline for is *visiting* other galaxies. Take too long and civilization will miss that boat permanently. Well, short of utterly breaking the laws of physics as we know them.

[jon-leonard.livejournal.com]

I guess I was making the trivial point that under a relativity+classical electromagnetism model, the effect shows up as an endless shift towards red. New light from the object can't reach us anymore, but it takes forever to clear out the light in between.

In terms of photons, there is some last photon (assuming certain kinds of expansion: A simple continuous linear expansion never expands to unreachability), but it takes a shockingly long time to go from the very-red-sky mode to an actual black sky. Would there be any stars left at that point?

[pearmeson.livejournal.com]

I would be very surprised if belief in that ancient mysticism was uniformly distributed. Have you ever read Asimov's short story (or the later novel) _Nightfall_?

[steuard.livejournal.com]

I'm considerably more fond of the short story than the novel. But yeah, now that you mention it, that's a great antecedent to this sort of philosophizing. The question, I guess, is whether the knowledge will be passed down as formal scientific data or (as in Nightfall) merely as mythology or "lore".

[pearmeson.livejournal.com]

Agreed on the short story vs. the novel -- though at this point it's been so long that I'm a little hazy on what was in the novel that wasn't in the short story. As I recall, the most interesting extra detail in the novel was that it was the appearance of the stars, rather than the actual darkness, that was most crazy-inducing. I can well imagine our hypothetical future descendants simply unable to deal with the idea that there are others out there -- there's plenty of people who can't fathom it now.