A Gigajoule of Damage

[Anaraxes]

Originally Posted by Fred Brackin

once you've observed a supernova somewhere you'll know when that supernova's neutrino front will arrive everywhere else. Very patient species could use this knowledge to prepare for combat

Sounds like a good tactic for conflict on a truly galactic-scale (both space and time). Or multi-galactic; reminds me of the Stephen Baxter Xeelee series.

The supernova thing may not be a reason to omit fields on ships but it's a fairly good reason not to rely on force fields to protect habitats floating in the atmospheres of hostile planets like you sometimes see

I agree. Systems that have only active stability should raise some engineering eyebrows. For example, there are schemes for dynamic beanstalks that avoid the necessity for the super-strong materials needed by the passive designs that just hang in place. But of course, if something goes wrong, down it comes. I don't have that much confidence in any human engineering.

But if you have the long view, there aren't that many cities that have survived for a thousand years, certainly not intact. Maybe that very patient species with FTL doesn't care if they lose a city on a planet here and there. That planet (might as well assume all the cities there have the same vulnerability) is only one part in 10^11 or so of their populated worlds. Earth gets by letting 0.8% of the population die every year, a million orders of magnitude higher. Their FTL probes can outrun the neutrino wavefront to warn locations of the date of their impending peril. (If they're like humans, they'll just drag their feet and not do actually anything for centuries until the neutrinos are almost there, and then have some sort of crisis response in the last few decades.) Neutrino taking out forcefields might even be just one of the little factors in total galactic teradeaths that mean no one really pays attention. When was the last time you worried about drowning in a gas heavier than oxygen? (Happens multiple times every year in the US...)

[Ulzgoroth]

Originally Posted by Anaraxes

I agree. Systems that have only active stability should raise some engineering eyebrows. For example, there are schemes for dynamic beanstalks that avoid the necessity for the super-strong materials needed by the passive designs that just hang in place. But of course, if something goes wrong, down it comes. I don't have that much confidence in any human engineering.

But if you have the long view, there aren't that many cities that have survived for a thousand years, certainly not intact.

Nothing is passively stable in the long run and very little except pure structure is even in the medium run.

System stability is only a mitigator for outage preparedness.

[Varyon]

Originally Posted by Fred Brackin

You also get the "problem" (common to FTL but not the worst of the FTL problems)that once you've observed a supernova somewhere you'll know when that supernova's neutrino front will arrive everywhere else. Very patient species could use this knowledge to prepare for combat when they know force fields wii be out (which will probably not be at anywhere near the same time for their home system) but their targets may be surprised.

I dunno, a group of marauding aliens trailing the neutrino front of a supernova to attack unshielded systems sounds metal AF to me, I'm not really seeing a problem from a setting standpoint. I'd be tempted to steal the name of the Supernova Dragon Lords from Star Power (although their methodology reminds me more of the First through Eighth Worm Holes, compressing the long stretches between attacks into short moments by traveling sufficiently close to lightspeed for extreme time dilation to come into play).

Originally Posted by Fred Brackin

The supernova thing may not be a reason to omit fields on ships but it's a fairly good reason not to rely on force fields to protect habitats floating in the atmospheres of hostile planets like you sometimes see (as in the vignette at the front of UT's Defenses chapter).

Yeah, as cool as those habitats are, with forcefields that can be shutdown by neutrinos they're going to be a non-option (forget supernovae - a hostile can just spray your general area with neutrino beamers, as you'd really only need a small hole for a catastrophe under those conditions).

[Rupert]

Originally Posted by Anaraxes

But if you have the long view, there aren't that many cities that have survived for a thousand years, certainly not intact.

There are quite a number of cities in Europe and Asia that are over a thousand years old. Many would be unrecognisable to their inhabitants of a thousand years ago, but it is in the nature of cities to change, to grow and shrink, to tear down and to build.

[Anthony]

Originally Posted by Anaraxes

But if you have the long view, there aren't that many cities that have survived for a thousand years, certainly not intact.

I would say that most cities that existed a thousand years ago still exist today, though they certainly look different today.

A majority of cities today probably didn't exist a thousand years ago, particularly outside of Europe and Asia, but that's not because of old cities dying, that's because there are more cities today than there were a thousand years ago.

[Farmer]

Originally Posted by Rupert

There are quite a number of cities in Europe and Asia that are over a thousand years old. Many would be unrecognisable to their inhabitants of a thousand years ago, but it is in the nature of cities to change, to grow and shrink, to tear down and to build.

Indeed:

https://en.wikipedia.org/wiki/List_o...habited_cities

Even some buildings can last centuries or more and still be in use:

https://www.grunge.com/327172/the-ol...-in-use-today/

[Anaraxes]

Originally Posted by Rupert

There are quite a number of cities in Europe and Asia that are over a thousand years old.

Originally Posted by Anthony

I would say that most cities that existed a thousand years ago still exist today, though they certainly look different today.

Not unscathed. I don't mean simply some settlement in the same place, whether keeping the same name or not. I mean a city that indeed hasn't changed, nor suffered any disasters in the sense of the post that kicked off the sub-thread (a forcefield failure in a locale where the city has to have the forcefield to survive). So, no Great Fire of London or Chicago, no Johnstown Flood, no San Francisco, Lisbon, or Tokyo Earthquake, no Pompeiis or Santorinis. Certainly people could come back and rebuild after a disaster, and often do -- but then, the hypothetical starfaring civilization could repair or rebuild those Ultra-Tech cities, too. If the possibility of a once-a-millennium disaster logically prohibits those cities from existing, it'd rule out most ancient Earth cities from existing as well.

[Fred Brackin]

Originally Posted by Varyon

I dunno, a group of marauding aliens trailing the neutrino front of a supernova to attack unshielded systems sounds metal AF to me, I'm not really seeing a problem from a setting standpoint.

Technically advanced groups that can build heavy force field using civilizations but who know less astronomy and physics than I do should be rather rare. Send scout ships 100 ly in every direction and you've got a century of warning time.

[Anthony]

The big problem with 'disabled by neutrinos' is that a nuclear bomb produces neutrinos, at a similar ratio to the sun. The sun's power output is about 3.8e+26W (9e+10 megatons per second), so if the sun disables force fields at 5 AU (750 million km), a 1 megaton nuke disables force fields at 1/300,000 that distance or 2,500 km.

[whswhs]

Originally Posted by Anthony

The big problem with 'disabled by neutrinos' is that a nuclear bomb produces neutrinos, at a similar ratio to the sun. The sun's power output is about 3.8e+26W (9e+10 megatons per second), so if the sun disables force fields at 5 AU (750 million km), a 1 megaton nuke disables force fields at 1/300,000 that distance or 2,500 km.

If the sun disables force fields at 5 AU you can't use them on Earth at all, and you can just barely use them on Jupiter. That might delay their development.

For that matter, does Jupiter have any neutrino output? I understand that it releases a fair amount of radiation as usually understood.