Tech Level Question

[RyanW]

Originally Posted by malloyd

If faster speeds were possible, light would travel at them. As should anything else massless in the absence of some other sort of resistance to motion - which is also what connects FTL to "negative mass", and the reason why stable wormholes aren't as problematic - as long as they don't form faster than light, they aren't actually FTL, because once you open them light can travel through them too.

I'm no expert on the subject, but wouldn't the speed of light be the asymptote at which massless things travel? Zero mass inevitably puts you at that point. It's just that the other side of the asymptote is only occupied by things that, as far as we know, don't exist.

[Anthony]

Originally Posted by RyanW

It's just that the other side of the asymptote is only occupied by things that, as far as we know, don't exist.

Well, they'd need imaginary rest mass. Also, if they interacted with gravity they'd produce gravitational bremsstrahlung, causing them to lose energy -- but for FTL objects with positive energy, energy decreases with increasing velocity, so they'd accelerate to infinite velocity.

[maximara]

Originally Posted by malloyd

In fact they are equivalent statements - "a kind of negative mass exists that will allow FTL" is the same statement as "effects can happen even if their causes never do". Something that often gets lost in FTL discussions is that the speed of light isn't actually about *light*. Light happens to go that fast *because* it's the fastest possible speed in the universe.

If faster speeds were possible, light would travel at them. As should anything else massless in the absence of some other sort of resistance to motion - which is also what connects FTL to "negative mass", and the reason why stable wormholes aren't as problematic - as long as they don't form faster than light, they aren't actually FTL, because once you open them light can travel through them too.

As pointed out in the Alcubierre Warp Drives segment Spacetime itself can travel FTL. In fact some Galaxies we see are ,per the Hubble constant, going FTL speeds What we are seeing is the light they emitted before they went beyond our Event Horizon

[Anthony]

Originally Posted by maximara

As pointed out in the Alcubierre Warp Drives segment Spacetime itself can travel FTL.

It's not clear that it can do so in any useful condition; the Alcubierre metric involves energy densities exceeding the Planck temperature, which is pretty much undefined behavior.

Originally Posted by maximara

In fact some Galaxies we see are ,per the Hubble constant, going FTL speeds What we are seeing is the light they emitted before they went beyond our Event Horizon

Not quite, but it is true that some galaxies where light's travel time exceeds the age of the universe. However, the normal causality problems with FTL go away because it is impossible for us to communicate with them, or vice versa (if we send a signal to them, it will not arrive).

[malloyd]

Originally Posted by RyanW

I'm no expert on the subject, but wouldn't the speed of light be the asymptote at which massless things travel? Zero mass inevitably puts you at that point. It's just that the other side of the asymptote is only occupied by things that, as far as we know, don't exist.

I'm pretty sure the formulation of negative mass you need for FTL type applications has a "rest" state at infinite velocity, and slows down asymptotically toward the speed of light as you add energy to it.

How you do engineering with something you can't slow down enough to interact with it is one of the issues glossed over in warp drive theorizing. I think it may be related to the "no way to turn it on or off" problem though.

[maximara]

Originally Posted by whswhs

The classic definition of "hard science fiction" seems to be SF that follows the Wellsian method: Make one assumption that is contrary to known fact and then work out the consequences logically in a way consistent with the rest of known fact. (Not that Wells always followed that rule; I've read a ltter of his where he called out the Invisible Man's ability to see as something he had handwaved for the sake of the story.) You do get that one assumption, though. Science fiction is more like mathematics than physics.

"In discussions of science fiction, “hard SF” refers to stories in which the science is as accurate as possible, and usually the focus of the story as well." - GURPS Space

..."science fantasy can have its own varying degrees of realism. If the magic is tightly defined and the interactions between magic and science are carefully thought out, then it can be just as realistic as any moderately hard SF with one or two bits of imaginary science. The magic just fills the niche of “rubber science.” A great example of highly realistic science fantasy is the GURPS Technomancer setting, which blends “technothriller” technology with rigorously explored magic, and addresses all the social and political implications of industrial- scale magic in a scientific and rational society." - GURPS Space

Countdown (1968) is hard science fiction while Robinson Crusoe on Mars (1964) is "soft" science fiction.

[AlexanderHowl]

What is considered 'hard' science fiction is dependent on the current technology and society. In 1880, having steam powered spacecraft was hard science fiction. In 1940, having atomic rockets was hard science fiction. In 2000, having the Internet be useful for anything but wasting time on social media, breeding bigots, and feeding trolls was hard science fiction. The definition of hard science fiction in 2040 may be using geoengineering to return to a stable Earth climate.

[Fred Brackin]

Originally Posted by AlexanderHowl

In 1940, having atomic rockets was hard science fiction.

Almost certainly too early. 1940 is just barely after the Hahn-Meisner chain reaction but before the (highly classified at the time) University of Chcago pile. Maybe 1947 for Heinlein's Rocket Ship Galileo. That had a recognizable "atomic rocket". Before that there was effectively no hard science SF in terms of propulsion.

[David Johnston2]

Originally Posted by AlexanderHowl

What is considered 'hard' science fiction is dependent on the current technology and society. In 1880, having steam powered spacecraft was hard science fiction. In 1940, having atomic rockets was hard science fiction. In 2000, having the Internet be useful for anything but wasting time on social media, breeding bigots, and feeding trolls was hard science fiction. The definition of hard science fiction in 2040 may be using geoengineering to return to a stable Earth climate.

Steam powered and atomic spacecraft are still hard science fiction. Using a nuclear reactor to heat water to steam for reaction mass remains a very credible approach.

[whswhs]

Originally Posted by maximara

"In discussions of science fiction, “hard SF” refers to stories in which the science is as accurate as possible, and usually the focus of the story as well." - GURPS Space

Yes, but "as accurate as possible" does not mean "completely accurate." If GURPS Space said otherwise, it would be contradicting the history of science fiction as a literary genre. For example, the work that is often considered to be the prototype of hard SF, Hal Clement's Mission of Gravity, has a rigorously worked out description of a superjovian planet with extremely high gravity and fast rotation . . . but there are humans there, who seem to have arrived from another solar system in less than a single human lifetime and expect to report back, so it gives every evidence of having FTL. This fits what GURPS Space actually says, which is that SF commonly has "one miraclle." Postulating such a miracle and working out its implications seems to be what hard SF mostly does, and I think GURPS Space is consistent with that.