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Science Sidebar 2: Dark Matter

2014/07/31 1 comment

Another item that didn’t make the paper.

So, dark matter.  It’s stuff.

The comment is prompted by the announcement a little while ago that the US Department of Energy has chosen which three next-generation direct detection experiments it’s going to fund.

So, what is dark matter, and what are these experiments doing, anyway?

This is a doodle I made once of a sparticle, or supersymmetric particle.  Dark matter WIMPs may be sparticles.  (No, it's not an insult, stop waving that spear around.)

This is a doodle I made once of a sparticle, or supersymmetric particle. Dark matter WIMPs may be sparticles. (No, it’s not an insult, stop waving that spear around.)

Cold Dark Matter Search

Dark matter is like the force: it surrounds us and penetrates us, and binds the universe together.  (Thank you, Obi-wan.)

We know dark matter exists because we can see its effects on ordinary matter, which has a convenient tendency to glow in the dark.  We see stars orbiting around their galaxies too fast to be held in place unless there were dark matter we can’t see; we see galaxies orbiting each other, or in clusters, at such a great velocity that they would fly apart… unless there were dark matter.  And on and on.  There’s also evidence for the existence of additional, weakly-interacting matter imprinted on the Cosmic Microwave Background (CMB), the afterglow of the Big Bang.

There’s more evidence than I want to go into right now, but if you’re still skeptical, check out the Bullet Cluster.

The predominant current theory is that dark matter is a weakly interacting massive particle — or WIMP, because physicists can’t resist a good acronym.  Something like a supersized neutrino — bulky instead of super-light, and only interacting very infrequently with normal matter.  We’re inside a galaxy, so there’s conveniently a lot of dark matter around and in us all the time, but it generally doesn’t do much.

This is where CDMS comes in, with SuperCDMS as the successor.  Both versions work with large chunks of germanium or silicon metal, waiting to get lucky and have a dark matter particle slam into one of the nuclei.  Those particular elements are chosen both because they’re a convenient mass (close to the DM particle), and because they have nice properties for detecting collisions.

To avoid confusion with other particles (like neutrons from radioactive decays or cosmic rays or other things like that), the whole experiment has to be way underground.  The same is true for…

LUX-ZEPPELIN

Nope, it’s not a band.  And the acronym gets shorted to LZ.  They’re combining two previous experiments into one collaboration.  This one is similar in principle to SuperCDMS, except that it uses liquid Xenon instead of silicon or germanium.  (Cool, right?)

Anyway, the main difference in results is that LZ will be more sensitive to higher mass WIMP-type particles than SuperCDMS is.  But, there is a region of overlap: low-mass LZ may overlap with high-mass SuperCDMS, allowing the two different experiments to cross-check each other.

It’d be cool if dark matter existed there.

ADMX-Gen2

This is where stuff gets weird.  Weirder.

This experiment doesn’t try to detect dark matter with atoms.  Instead, it’s using microwaves.  It’s looking for a particle called an axion, which is much less massive, and hypothesized to have some strange properties when it interacts with light.

That particle was postulated to solve a fundamental problem in particle physics related to what’s called “CP violation”, but maybe it can handle the dark matter problem as well.  It’s not as popular as some of the more massive WIMP theories, but it should still be tested.  Since we don’t know what the right answer is yet.

 All The Other Things

Yes, there are lots of other experiments.  I have serious doubts about their claimed detections, though.

Also, it’s quite possible that dark matter is more than one thing.  Hey, maybe it’s two different kinds of WIMP, plus axions and something else we haven’t thought of yet.

And that’s that.  … no, let’s leave dark energy for another day.

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Science Fiction Round 32: Paycheck

2014/07/23 Leave a comment

The film is Paycheck.  The basic premise is that the lead character, Michael Jennings, works for companies to reverse-engineer their competitors’ technology, and then have his memory wiped when he’s done.

The general theme is [GIGANTONORMOUS SPOILERIFICNESS].

Now that that’s out of the way, let’s do some analysis.

 

This is Jennings.  And yes, the train tunnel actually shows up in the movie.

This is Jennings. And yes, the train tunnel actually shows up in the movie.

The Author Is A Spoiler

The movie is based on a short story written by some guy named Phillip Dick.

Given that he’s the author behind the original print versions of Minority Report and Blade Runner, as the poster above says, among other things, you can infer that mind-bending is imminent.

I am reminded of Achron in many ways.  The last job Jennings takes is to [SPOILER] help build a machine that can see into the future.  No time travel, mind you, just see the future.

Turns out, seeing the future makes the world go bonkers in the future, more or less, so Jennings has to set things up so that, after his memory is wiped after the job, he can destroy the machine that lets people see the future.  And uses his past future knowledge to make it work.

Reverse-Engineering The Future

That’s how Jennings approaches the whole situation.  Before his memory is wiped, he uses his foreknowledge to send himself a package of useful goodies.  Once he’s back out in the world, he’s confused about why he gave up his payment… and why he sent himself a back of junk.  A few “coincidental” convenient things push him to realize that he sent himself a bag of tools that he would need to change the future.

Admittedly, this is pretty cool.  Solving the puzzles along with him and watching how small things can change the course of events is great fun.

There’s just one part that has me concerned.

A huge world-war in the wake of future-viewing tech (predicted by said tech) is what causes Jennings to send himself a package in the future to make sure he destroys what he created.

Now, this is all well and good.  Except, he and a friend go back to the machine to destroy it… after looking into the future one more time.

That “one last look” showed Jennings getting shot on a catwalk.  Jennings sees this, and plans to change the future to work around this issue.

But… in between his successful escape and his reading of the future, one of the bad guys has access to the machine.  And looks at what Jennings was looking at, to see him getting shot.

But, if Jennings had changed the future to avoid getting shot, why wasn’t the evil executive able to change the future such that Jennings did get shot?  The only way this makes sense would be if the bad guy was looking at a record of what Jennings saw, rather than the actual future… which isn’t made explicit.

Bad Guy Computer Security

I think the villains had the idiot ball in this one.

I mean, seriously.  You didn’t make backups of the plans for the future-watching device?  You aren’t most of the way done building a second one at a separate facility?  You just let Jennings back into your facility to get at the machine?  You assume he could only be going in there for the power of seeing the future, despite the fact that you know about all the looming disasters if the machine continues to exist?

… yeah.  That, and, to some degree, I think the premise of the device itself is an issue.  Seeing the future inevitably means war, plague and devastation?  I think the problem is that people seem to assume the future is immutable… or their attempts to mitigate that future, cause it to happen… in the future.  Very confusing, of course.

But, for once, could the future we see be a good one?  And our efforts to bring it about cause it to happen only once we see that it can happen?  Or, alternatively, seeing that the future can be good causes everyone to be complacent, leading to a worse future, necessitating the destruction of the device

That might be a more interesting twist.

Categories: Clement's Game Tags: ,

Your Turn, Round 2-6: A Little Rapid World-Building – Tāwhiri

During a discussion I participated in elsewhere , science-fiction world building spontaneously appeared in a discussion of another subject when a couple of people brought up the example of floating forests / floating islands.  These have shown up in fiction before, and also in real life.  I was inspired to add them to the Fermi Problems setting.  When I had a notepad and a little time, I designed a planet to put them on and named it Tāwhiri.

What Is A Floating Forest?

When I say “floating forest” here, I mean a large mass of vegetation floating in a body of liquid.  Perhaps there is too much similarity here to the micro-gravity asteroid-surrounding forests and floating aerogel-clumps that already feature in the setting, but I will include it anyway.  It is relatively straightforward to produce a planet where such islands occur to a much greater extent than they do on Earth:

Consider an ocean gyre like the Sargasso Sea.  Have masses of floating seaweed-equivalent that grow densely enough and stack thick enough to give a portion of the mass that is persistently well above the water line – avoids the photosynthesizing bits getting shadowed by or eaten by other stuff growing in the water.  Then the clumps that are strong enough to avoid being disrupted by frequent waves/wind have a survival advantage, because they keep their energy supply more reliably.  To get something that looks like a terrestrial forest, rather than a lumpy-mat-berg-plant-thing, invoke selection for traits that keep the clump in the gyre and so at a good latitude for growing.  Growth dependence based on sunlight illumination patterns can do that, and progressively give “trees” with trunks and sail-leaves that adjust themselves unintelligently to take advantage of prevailing winds and stay in the gyre.

Some clumps will still escape, and either freeze in cold water or die in too-warm water or end up in another gyre.  Clumps that get too big will fragment during storms, some will have die-offs due to competition between the various species that accumulate to form the colonies, some may capsize and persist as dead-or-dying rafts that can be colonized by new growth, and so on.

Tāwhiri – A Waterworld

But how to make a planet where these floating forest-mats are the tallest-standing lifeforms?  We need to avoid having much land-based life to compete with.  We need a waterworld.

There is a problem with making a world that is entirely covered in water: Carbon dioxide emitted from the mantle during volcanism enters the atmosphere/ocean, and acts as a powerful greenhouse gas.  Unless it goes into making limestone or something similar, biosynthesis of carbon compounds only keeps so much of the carbon out of the atmosphere and only for so long.  On the Earth, weathering processes on rocks exposed to the air create carbonate rocks, which eventually get subducted and return the CO2 to the mantle.  If there is no exposed land at all, this process doesn’t work and the climate tends to run away into a steamhouse atmosphere, which is not conducive to abundant life.  So I will do a little fine-tuning on the volatile content.  The planet we are considering will have just enough water to cover all but 1% of the surface – we have various small exposed, largely volcanic, pieces of land; and larger relatively shallow areas of ocean that we would call submerged continental fragments if they were on Earth.  This is enough to give a stable climate, albeit one with more CO2 in the atmosphere than we humans can breathe:

  • Mass: 0.95 Earth masses
  • Insolation: 340 W/m^2 average.
  • Mean surface temperature: 300 K
  • Atmospheric pressure: ~1.1 atm, 0.01 atm CO2

That surface temperature is a few degrees hotter than Earth was during the Permian, and is such that there are no ice caps at the poles.  Some additional properties follow in part from the above and in part by arbitrary decision:

  • Host Star: Kiwi – 0.85 solar masses, 0.43 solar luminosity
  • a = 0.7 AU, year = 0.635 yr (291.4 local days)
  • Mean solar day: 19h6m.
  • Two satellites, each between 30% and 50% the mass of the Moon.

The relatively-shallow regions of the ocean also serve a useful setting function: they give a pattern of gyres and overall surface currents that is more-or-less fixed relative to the seafloor, rather than drifting around the planet.  Keeping the maps straight will still be annoying, but at least a given gyre will stay over the same geology.

Technology

I am also pleased to assume people living in/on these floating forest-mats.  Their cultures, history, anatomy, and evolution are not yet specified – this is a rapid once-through, after all.

But consider this technical problem: where do you get metal if you live on this world?  There are several possible sources: those few areas of dry land that do exist, sulfide or hydroxide deposits on the sea floor, and some manner of catalytic process that separates out the metals dissolved in the sea water.  The last has a terrestrial precedent: a ~3-cm snail called the scaly-foot gastropod that hangs out near some deep-sea vents:

Scaly-Foot Gastropod.  That shell is coated in iron sulfide.  via https://www.jamstec.go.jp/e/about/press_release/20091130/

Scaly-Foot Gastropod. That shell is coated in iron sulfide. via https://www.jamstec.go.jp/e/about/press_release/20091130/

So there are ways to start developing the hardware necessary to get off-planet and start expanding through space, although it would be somewhat more difficult than doing so on Earth.  I will have the inhabitants of  Tāwhiri in the Fermi Problems setting not have done this yet, in keeping with the large gaps in the setting between the number of places where life has appeared, the number of places where cultures have appeared, and the number of places where cultures have spread across large volumes.

Fantasy Round 28: How To Train Your Dragon (2)

2014/07/07 1 comment

It’s a bird, it’s a plane… nope, it’s a dragon. It’s How To Train Your Dragon 2, and I’ve got to admit, I’m a bit disappointed in the sequel.  I really liked the first one, so a degree of disillusionment was perhaps to be expected, but… I’d really like to rewrite the plot.

I’m going to comment on a couple of points that are common to both movies, and then move on to specific annoyances in the sequel.  As ever, spoilers!

Aha, the characters are now older, young adults.  But still mostly smaller than their parents.  Weird.

Aha, the characters are now older, young adults. But still mostly smaller than their parents. Weird.

Read more…

Science Sidebar 1: Things That Go Boom In The Night

2014/07/01 2 comments

Since I’m currently working as a science reporting, I’m writing a whole bunch of actual non-fictional things about science.

The catch?  Since the newspaper is not my personal blog, there’s finite space.  So I don’t have room to include all the cool details.  Which made me kind of sad, until I realized that, hey… I could put some of those details on my personal blog.

Life is good.

And thus, this, the first installment, just in time for the Fourth of July.

sn1006c

Courtesy of Astronomy Picture of the Day (who got it with credits to NASA, ESA, and Zolt Levay), here’s SN 1006 — the remnant of a Type 1A supernova. Nice celestial fireworks. (Suffice it to say, don’t set off one of these in your back yard.)

The article I’m referring to is available online here.

So, what didn’t make it into the article?

Read more…