Monday, January 28, 2013

Gas Giant Planets--open for settlement?

When looking for new homes for the human race, people generally think of worlds like Earth, that is, planets with a solid crust and liquid water oceans, places where plants might grow and animals might be available to eat. Sometimes people expand this to include lifeless moons or perhaps moons or worlds with trapped water, like Ganymede or Mars. But why shouldn’t we consider living on worlds not like Earth at all? Why not gas giants, like Saturn, Uranus, and Neptune?

Clearly a planet just like Earth would be a better place to live if your level of technology were in, say, the Stone Age. But with a higher level of technology—hey, even with twentieth century technology—the challenges of a world radically different from Earth, like a gas giant, don’t really pose a problem. Can’t breathe the air? Solve that by living in controlled atmosphere habitats. No solid surface to set down on? Float your giant living habitat on balloons. No plants or animals to eat? Grow or raise your own in your hydroponic gardens/animal pens.

If you ask the question, “What does a planet really need to offer for a human being to survive?” technology makes the number of specific things required less than they otherwise would be. Perhaps the main thing a planet needs to offer is resources—energy sources and building materials. It might seem at first glance a gas giant would not offer enough of what humans really need, since we build in metals and glass and the atmosphere of a gas giant is mostly light gasses like hydrogen, helium, methane, and carbon dioxide.

But if you build your habitats out of carbon-composite materials, you have all the carbon you could ever need in the atmospheric methane and CO2. You just need to extract it. A byproduct would be oxygen and hydrogen, or water if you choose—though the atmospheres of most gas giants have plenty of water vapor anyway.

Orbital astronaut experience has shown that gravity is essential for humans to live normally—and guess what? In the atmosphere of the three smaller gas giants in our Solar System, the amount of gravity you’d experience is roughly equal to that of Earth (Jupiter, though, would be far too much gravity for humans).

You could adjust the height and latitude of the craft to match a zone where the pressure and temperature is similar to that of Earth’s atmosphere. The magnetic fields and atmospheres of these worlds would do you the favor of protecting your settlers from dangerous solar and cosmic radiation. And you could add to your habitat from available carbon on an unlimited basis, provided you had the energy to process it—and plenty of energy would be available by harnessing wind power (and plenty of deuterium would be available for hydrogen fusion).

An advantage to settling a gas giant would be that it would take a very, very long time to run out of available room, since these atmospheres are massively huge by Earth standards. Plus, there seems to be a great many gas giants orbiting not just our own star, but others. Note a similar technique could be used to settle the atmosphere of a hot world with a dense atmosphere like Venus. Perhaps the floating habitations there could fly above the clouds, not unlike the Cloud City of Star Wars fame…

A disadvantage to a gas giant settlement would be entering and exiting its atmosphere. Yes, the density is of these worlds is lower, reducing the sensation of gravity if you were in their atmosphere—but they’re still very massive. There’s a lot of gravity to fight in coming and going, not to mention wind resistance. It would be much harder for a spacecraft to exit Saturn for a trip back to Earth than, say, Mars.

Another problem comes from the massive storms whipped up by the atmospheres of these worlds. The storm problem might be insurmountable, in fact. Very fast winds aren’t so much a problem—it’s when the winds change speed and direction so rapidly they would break a human habitat in half—or at least splatter the humans inside against the walls like jelly...

Still, certain gas giants could have layers of great stability, where the atmosphere maintains consistent conditions over essentially indefinite time…that’s something you’d want to discover before establishing the settlement, of course. In general, though, it seems the further away from the sun (or for extrasolar worlds, its star) a world is, the more stable and consistent its atmosphere. So, it seems that Neptune is more stable than Saturn, perhaps stable enough to settle without problem…which is interesting and ironic in that like Earth, Neptune is a blue world…

What if aliens had already settled gas giants and had discovered means to create areas in which the storms are less dangerous? Saturn has a permanent storm pattern around its south pole shaped like a giant hexagon. What if this area were a place of massive alien settlement? Or what if Jupiter’s Great Red Spot, which human scientists see as a giant storm, is a deliberate attempt to create a predicable storm—where the winds change in a regular way, supporting hundreds of millions of alien habitations floating on giant balloons in the midst of the Jovian atmosphere...they'd actually be a lot harder to detect than you might think...


Monday, January 14, 2013

Antigravity (really!)

The term "antigravity" is really the stuff of science fiction rather than a term in common use in the scientific community. As such, it's rather ambiguous and could refer to multiple things. One idea pioneered in a story by H. G. Wells was a substance called "Cavorite," which would effectively block gravity's pull, allowing an object to lift away from Planet Earth (the tale was The First Men in the Moon). Other proposals have featured gyroscopes or electrodes or magnetic fields canceling out or altering gravity in a way similar way to Cavorite. Please note there has never been any realistic theory of any means by which a substance could block gravity (though under the right circumstances, magnetism really can counteract it). Under Einstein's General Relativity, gravity is not really a force at all--its sort of a side effect of the existence of matter/energy, which causes the structure of space to bend...well, more correctly, to compress. Any physical thing made of any form of known matter would merely add to that effect...

It so happens I did a previous post on the Higgs Boson in which I suggested that if it were possible to block the Higgs Field, you could wind up with an effect somewhat like the type of antigravity Wells imagined (because objects would loose mass), depending on details. Of course, as I understand the situation, there does not exist even a wildly hypothetical proposal for blocking the Higgs if conformity to what's possible in physics is a writer's goal, no story would be able to feature a "Higgs Field suppressor." If physics doesn't matter to you, hey, have fun...:)

Alternatively, antigravity has been imagined as a force that would work exactly the opposite the way gravity does--that is, it would repel all objects instead of attracting them. This idea in fact almost has a basis in theoretical physics. In the post previous to this one (on Realistic Warp Drive), I mentioned that something called "Negative Energy Density" would be required to create a warp drive field. So--if under General Relativity as mentioned above, gravity is the compression of space in response to the presence of mass/energy (really the energy is the important part--remember matter can be converted to energy via E=mc2), what would happen if you had an object that contained negative energy? Ignore for a second that "negative energy" seems to make no sense at all--IF you could produce such a state, negative energy would cause space to expand rather than contract, right? Yes, in fact it would.

Negative energy "antigravity" would thus allow you to expand space to make a tunnel to another region of space, a.k.a. a "wormhole." This kind of antigravity would also be required for warp drive, which would use regular gravity to contract space in front of the craft and "negative energy density" to expand space behind it.

An interesting side effect of an object with negative energy density is that it would be gravitationally drawn toward  "normal" matter, because even though its gravitational force would be repulsive, its negative mass would respond by accelerating in the opposite of the direction of the force (which is a bit like if you filmed a car driving backwards and then replayed the film in reverse order--the car would appear to move forward). But normal matter would still be repulsed by matter with negative energy--so the negative energy density object would in effect "chase" the normal matter, never catching it if they were of equal mass, both continually accelerating faster (even though both accelerating, the total energy of the masses would cancel out, since the regular matter would gain regular energy and the negative matter would gain negative energy). 

Yes, you could make a kind of engine out of matter with negative energy density, if you had any. The problem is, how in the world could anyone have such a thing as "negative energy density" or "negative energy"? That's all hokum, right? 

Well, most likely. But there may be something more realistic that has a similar effect.

Antimatter, a very real substance with electrical charges opposite to normal matter, which has been manufactured in tiny quantities in high energy physics labs, most definitely has a positive energy density. When matter and antimatter collide they both instantly become energy--the total energy being equal to the mass (ran through E=mc2) of both the matter and antimatter.

However, certain attempts to harmonize quantum mechanics with relativity have considered that there must be a particle of some kind that actually does produce a force to bend space, in contrast to Einstein's understanding of gravity. Attempts to work out the mathematics for this particle, called a "graviton," also propose another presently unobserved particle, something called a "graviphoton." The graviphoton would produce another force, currently unconfirmed, that would be similar to gravity, only weaker and with a finite range. This force would add to gravity's pull on normal matter, but would repel antimatter.

So could such a force, one that repels antimatter, be employed in future technology? Future warp drives and the like?

The ability to repel antimatter certainly would come in handy if you're trying to keep the stuff from blowing up...the problem is of course that regular gravity would still apply so this repulsion force would be fighting against the ordinary gravitational attraction of matter (and antimatter). In my reading I couldn't find any reference to the idea that a graviphoton would cause space to expand--though since we're talking stories here and not physics, it could be imagined to do so. 

It could be possible in theory to build a spacecraft or aircraft that produced all the effects we normally associate with antigravity...the problem is, you might have to make your craft out of know, just the most highly explosive substance in the known universe...perhaps a little trifle of a problem...

It certainly would be--though now I feel an urge to entitle a story, "Captain Elijah's Antimatter Chariot"...


Sunday, January 6, 2013

Realistic Warp Drive (well, sort of...)

 (image by author)

NASA's Dr. Harold White in a paper last year argued that warp drive is realistically possible in terms of the energy requirements to bend space. How a warp drive would work  would be to expand space behind the craft while contracting it in front of the craft (just as imagined in Star Trek). Expansion behind and contraction before would in effect "push" the craft forward.

Well, it would create a bubble of space (and time) that would surround the craft and push that forward...the craft within the bubble would never exceed the speed of light and according to the best theoretical knowledge of physics, there is no limit to the speed at which space can be bent--er, "warped"--so this changing of the shape of space could create an effect that would make a vessel travel as if it were going faster than the speed of light. Note that this "warp speed" acceleration would not produce actual inertia, so Jean-Luc Piccard saying "engage" would not cause the crew to splatter against the far wall without some kind of inertial compensation (unlike how I previously discussed this topic in my post on Gravity and Starships)...

The equations based on the best understanding of the nature of space are well understood and a number of them are referenced in Dr. White's paper. The energy requirements are huge, but far less than what were thought necessary when this concept was first discussed by physicist Miguel Alcubierre in 1994 (this thesis ideas are covered in this link). The energy is in fact comparable to the energy requirements for a realistic trip in normal space (see my discussion of Project Valkerie in my Nanite Space Weapons post).

One major drawback would be that this bubble of normal space would tend to pick up particles of normal matter as it travelled along. Then once you shut down the warp drive, those regular pieces of matter--most of them would be small particles--suddenly continue on moving with the inertia they had when you picked them up...and space is full of very fast moving particles.  It would create in effect an enormous blast of high moving particles, most likely going every direction. Very dangerous for your ship...and whatever planet you happened to be visiting.

Though that's not necessarily so bad...if there were a way to direct these particles, the system could serve as a weapon. Drop out of warp drive and BOOM--no photon torpedos required. But if there were no way to direct them, that would mean you'd simply have to shut down the warp field on a regular basis to let them dissipate (hey, it would still be a lot faster than hitchhiking :).

So the Warp Drive I used to make fun of as silly mumbo jumbo turns out to be not so unrealistic after all...except for one minor detail...well, not so minor. It turns out to create the warp field in the first place you have to generate something called "Negative Energy Density." Which, while some physicists believe perhaps could exist, negative energy density has never really been observed to exist in a way that anyone even in the greatest leap of imagination could reliably generate...sort of a problem, right?

Anyway, this should by no means impair a science fiction writer's work. Just craft the tale with this itty bitty little problem (well, immensely huge problem really) already solved and you're good to go...

Oh, by the way, "negative energy density" is related to something you could call "antigravity," which, if it existed, would be some really weird and certainly story-worthy stuff. But I'll cover that next time...