Altering the Past, part 1 September 11, 2011
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Discussions of time travel among physicists never fail to revolve around a rather jargon-y term: “closed timelike curves”. The exact definition of this term is not important right now. What is important is that it fixes the discussion to the question of whether or not it is possible for a chunk of ordinary matter to revisit a previous point in its own personal timeline. This is a very interesting, very speculative, and oftentimes very mathematical question. Of course, it’s not the only discussion of time travel – consider your average time-travel science fiction story. With a few notable exceptions, the same thing always happens: our heroes are flung back into the past and they must find a way to return to their own time without changing history. Sometimes they succeed, sometimes they find they were meant all along to have done something in the past, sometimes they have to undo an accidental change they already made. Save history or else!, is always the message. Frankly, I think we could all do with a little less history these days, but that’s a digression for another time.
There is a question lying at the intersection of these two realms of time travel that I found myself recently pondering. What does it mean, in the context of a physical understanding of time and space, to have altered the past? How much of a disruption is small enough to go unnoticed, and how much is enough to make sure that the planet has been conquered by giant ants when you get back to your present day?
They campaigned on a platform of free sugar cubes. What were we going to do, vote for the spiders?
To get started on this, I will have to drop some physics on you. What you’re about to see is called a Minkowski diagram, and it is the best method ever devised by man for representing the fundamental, ethereal concept of causality in a drawing simple enough to be a doodle on someone’s coffee napkin.
Pictured: Cosmic wisdom.
There’s a lot going on here. Let’s unpack it. First, we have the horizontal axis, in light years. This represents all of space. On the vertical axis is time, in years. That means that a light ray, traveling one light year per year, is a 45° line. The tricky part is that these light rays represent the limits of temporal influence. Let’s say I, sitting at Here & Now, at coordinates (0,0), want to influence something three light years away, at x = 3. Let’s call this place Deep Space Three. The fastest way to do it is to send a signal of light. That light ray will travel for three years and then arrive at Deep Space Three, at coordinates (3,3). I absolutely cannot send any information to Deep Space Three, three light years away, any sooner than that. Any events that happen at Deep Space Three before that are utterly beyond my power to alter to even the smallest extent. I cannot so much as budge a single electron. Why? Because the light ray hasn’t gotten there yet. And the light ray carries the electromagnetic force. From currently known physical laws, all influence, all information transmission, happens through interactions of one or more of the four fundamental forces. Gravity, strong, weak, and electromagnetic. That’s it. For an object to be influenced in any way is for it to interact with another object via one of those forces.
Love is not a force, no matter what Randall Munroe tells you.
But now let us turn to the past. The diagram also shows all the points, events, and information that can possibly influence me, at Here & Now. Anything that can send me a light ray exists on one of the diagonal yellow borders of the triangle labeled Past. What about the rest of the triangle? It’s largely irrelevant. With one large exception, every single interaction you have ever had and will ever have with anything else in your entire life happens by the exchange of photons, carriers of the electromagnetic force. What you think of as physical touch is the exchange of photons between the EM fields of your skin and another object. Sound waves, pressure waves in air, are transmitted when one group of air molecules pushes another. That push happens by the same EM field photon exchange. Think about everything that’s ever happened to you. Every event, every point on your version of that graph, is an electromagnetic interaction. You have lived a life built out of light rays.
Oh man, remember this day? That was hilarious.
I’m afraid we’re out of time, dear readers. Next time I will, with this background fresh in your minds, discuss the meat of the question. And, I’m going to give you some homework. Just two questions, to roll around in your minds.
1) I mentioned a large exception in the final paragraph. What is it?
2) Try to think of minimal ways to change events. What’s the smallest amount of energy required to get someone to change their mind on any kind of decision, or alter their actions in some culturally recognizable way?
Happy sciencing!
The Impending Robot Upheaval April 7, 2011
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Futurism is a dangerous business. Historically, human beings have shown an ability to predict future events more than, say, a few days in advance that is, on average, much less effective than chance. And the greater the scale of these predictions, the more people involved in making the prediction a reality, the more abysmal our power of precognition becomes. Nowhere is this more evident than in claims about new or (allegedly) forthcoming technology, for the simple reason that technology is the single most rapidly changing field of human endeavor that has ever existed. How many times have we heard that this or that device will be The Next Big Thing, only to have it exert only minimal effect on the lives of those who use it, or only be used in very rare applications, or manifest only as a passing fad, or even never make it to a working prototype, much less the public market? The segway, blu ray, flying cars, laserdisc, video phones, blimps, jetpacks. The simple fact is that no matter how much it may seem to the engineer or the scientist that a given piece of technology will provide definite alterations to society as it presently exists, the economic and social responses are far too complex to anticipate.
So why is it, then, that the title of this essay predicts with such apparent confidence a staggering change to the way our world works as a result of a certain type of technology? Because in this case, the case I am about to present, the mere possibilities are stark enough that we should all be sitting up and taking notice. Risk analysis must be based on both the likelihood and severity of a potentiality; even if the likelihood is very low, the consequences may be severe enough that preparation is called for.
Advances in robotics have been accelerating. In the last ten years, amazing innovations have been made in robotic movement and information processing. As a theoretical physicist, I am trained very thoroughly in learning the basic elements of a system, then anticipating and evaluating the logical consequences. I find that at this point in my career I do this automatically, with almost every situation I come across. And so it was with what I learned today. As soon as I learned of the latest development, a connection was forged in my brain with other robotic inventions of which I already knew, and from the top of my head consequences sprang forth unbidden. Terrifying consequences. Consequences which might never, which hopefully never, come to pass. Let me show you the pieces of which I am aware – and recognize that there are almost certainly pieces of which I am not aware.
This one seems helpful, or at worst innocuous. It is the Brain Computer Interface, and researchers were stunned to find that making one is as easy as directly connecting an input chip to the nervous system. With adaptive software, the plasticity of the brain does the rest, and within a day the brain can, by thought, control whatever device is attached to the system. This video was posted in 2009, and newer BCI systems make this one look slow. Companies like Braingate and IntendiX are already putting these devices on the market and into medical applications. So what do you want to control with your interface?
How about a nice powered exoskeleton? One of these babies enhances strength, speed, and endurance by factors of anything from five to ten. The reaction time gets even faster if the input is from a well-trained neural interface.
Or how about one of these? A company called Boston Dynamics has developed robotic locomotion possessing balance and terrain capability on par with organic systems (you know, animals with legs). Available in regular size (seen there) and fun size.
But maybe legs are too, well, pedestrian. Enter the quadrotor. Developed by UPenn’s GRASP lab, these are autonomous hovering drones capable of astonishing feats of agility and cooperation. That one video does not do justice to their potential. They can do surveillance, dynamic flight adjustment, and cooperative transport of heavy objects. Did I mention they’re autonomous? That doesn’t mean true artificial intelligence, but it does mean that once you give them a goal (like “fly through the opening”, or “keep the ball in the air”) they get the job done without further instruction and by communicating with each other. Oh, and they’re already commercially available.
Now, this is the final piece, the one I found today. It’s not a physical invention, it’s software. Very, very smart software. Given a reference image on any object, this software will be able to track it in a visual field. Not only that, it learns as it watches and improves its tracking. It can pick out faces and objects in rapid, erratic motion. Oh, and it’s called “Predator”.
Some of you readers are already seeing what I see. Combine any of these inventions with any other, or with conventional weaponry, and you have something that the world has never seen, has never had to deal with. Combine a quadrotor, a predator-controlled camera, and a simple explosive. You now have a device that can search for, track, and destroy a specific human target or group of targets. Combine a BCI, a remote datalink, and a locomotive robot with some mounted machine guns, and you have a human mind that can power across a battlefield without suffering any pain. Combine enough quadrotors with any kind of mounted weapon and you have something that can only be described as a swarm.
I don’t know where all this is going. I don’t know which of the possibilities I see, if any, will come to pass. If they are used, I know not who will use them, nor in what way, nor to what purpose. I do know that there are powerful agencies on this planet. I do know that the first-world militaries already have access to all of these pieces, and may have had access for some time. I do know that there are large national and multinational corporations with billions of dollars and unchecked profit motives. I do know that across the world are millions of smart, young, bored people who all have access to some of these pieces, and who might as easily create something horrific as they might create something that will save the world.
Certainly there are many, many positive uses for all of these inventions. I fervently hope those are implemented. But positive or negative, the possibilities from these leaps in robotics are staggering. I am not the only one who sees that. So a change is coming. Bigger than a revolution, bigger than a mere cycling round of human powers. It will be a robot upheaval. When the full force of this entirely new phenomenon comes, it will introduce entirely new elements, and maybe even new members, to society. How can we be ready for this? I haven’t even the slightest idea. Comments, speculation, and additional questions are very welcome.
Physics Playlist April 6, 2011
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I trust this will speak – or sing – for itself.
1) “The Power” – Snap!
2) “Free Fallin’” – Tom Petty
3) “Sound Check (Gravity)” – Gorillaz
4) “She Blinded Me With Science” – Thomas Dolby
5) “Time” – Hootie & the Blowfish
6) “Bang Bang Bang” – Mark Ronson
7) “Under Pressure” – Queen & David Bowie
8) “Danger! High Voltage!” – Electric Six
9) “Absolutely Zero” – Jason Mraz
10) “Intergalactic” – Beastie Boys
11) “The Universal” – Blur
I’ve also composed it into a youtube playlist, for convenient listening, here. Meanwhile, share your favorite physics songs! What should I have included, or not included?
Physics Problem Error Code March 17, 2011
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Usually I try to aim my posts at, well, everyone. That is, after all, the point of this endeavor. But this time I’ve had an idea that might only make sense to those of you who have had to complete some sufficient amount of physics homework, or if you’ve ever had to grade any. For those of you who have been there, this will make sense. It may even make a staggering amount of sense. For those of you who are currently looking for something else to read, I promise that, if nothing else, what follows will grant you some insight into the way physics problems are solved.
It was while I was wandering through the barren and hostile wasteland that is a grading session that I began to wonder about streamlining the correction of common errors in the solutions. There are four main aspects to every physics homework problem solution, and so it is in these four categories that standard errors can be recognized:
Concept: of or relating to a student’s conceptual understanding of the system to be analyzed or the problem to be solved.
This category would seem at first to be the most complex: how do you navigate the murky qualitative waters of conceptual understanding? You don’t. You let the problem do it for you. Each correct solution, we will say, requires some set of correct conceptual statements, and each of these will either be implicitly stated or explicitly stated as required. Then the conceptual errors break down straightforwardly into the following categories:
C1) Omitted implicit conceptual statement
C2) Omitted explicit conceptual statement
C3) Incorrect implicit conceptual statement
C4) Incorrect explicit conceptual statement
C5) Logical fallacy
Now, the third one does have a bit of a wrinkle in it: In my experience, almost all of the implicit incorrect conceptual statements have been a result of incorrect mathematics, which would be taken care of by an error code in the Mathematics section. In other words, the logical consequence of an incorrect formula or equation give rise to a physical contradiction. However, in the interest of completeness I have included it, because I can readily imagine a student’s written words implying some incorrect concept.
Execution: of or relating to the choice of problem solving techniques used in a solution.
It’s a bit difficult at first, when considering solutions to physics problems, to draw a line between Execution and Mathematics. The key is choice: A student chooses to use F = ma and F = kx, she does not subsequently choose to obtain a = (k/m)x. Often there is overlap between the Concept section and the Execution section – choice of an equation to describe the system under consideration amounts to a statement of the properties of that system. Instructors will have to take care to discern whether it is incorrect physical understanding or incorrect problem solving method, or both, that has yielded an error.
E1) Insufficient clarity of procedure (read: “What ARE you doing here?”)
E2) Omission of required technique
E3) Omission of required formula or equation
E4) Use of incorrect or irrelevant formula or equation
E5) Inapplicable approximation
E6) Inappropriate quantitativeness in approach (Note: this can either be too much or too little)
Mathematics: of or relating to the use of quantitative or analytic methods to obtain an answer.
This one also seems complex, but similar to Concept we can use a few catch-all categories to simplify things. This section is also simplified by realizing that much of what seems like incorrect Mathematics is actually incorrect Execution.
M1) Insufficient clarity of procedure (see above)
M2) Omission of required technique
M3) Algebra error
M4) Calculus error
M5) Other math subtype error. Specify.
Numerical: of or relating to obtaining a specific number or set of numbers for an answer. Duh.
N1) Digit transposition.
N2) Incorrect choice of numerical input.
N3) Insufficient precision.
N4) Computer error.
And there you have it, ladies and gentlemen. These error codes should, by judicious combination, be able to address every possible mistake in solutions to any possible physics problem. The basic architecture here is based on my own experience in solving and grading physics problems, so I am biased, and it is possible I have missed something. I therefore encourage you to try to throw an exception to these rules! Give me your best shot.
Debunkation March 7, 2011
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Just because I want to spread the word on this as much as possible: You may have seen in recent days that Fox News posted an “exclusive” about the discovery of “extraterrestrial life”. You may have seen in the previous sentence the use of quotation marks. This is because the science that has been reported is extremely dubious at best. First and foremost, it was not published in a peer-reviewed journal. Second, it’s a pile of equine feces. I give you the introduction to PZ Myers’ take on this development:
No.
No, no, no. No no no no no no no no.
No, no.
No.
You can read the rest here: Did scientists discover bacteria in meteorites?
Quiet Re-Opening March 4, 2011
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After a long hiatus, Science In Real Life is quietly puttering along again, in this corner of the intertubes. No schedule of posts, no set format. Just me, my mission, and my audience (such as it is). I would appreciate any word-spreading you feel is appropriate. If you enjoy this blog, if you think you might someday enjoy this blog (tell me what you want to see more of!), if you like science … then this, for you, is a cause worth promoting. Now, to business. There are two more items to deal with in this post.
1) A snazzy new URL! Here at the Science In Real Life main office, we have secured for everyone’s convenience the URL reallifescience.org, or http://www.reallifescience.org, if you’re not into the whole brevity thing.
2) I have to take time to give a science shout-out to another author who has done perhaps the best job I have ever seen of illuminating what it means to think scientifically, to think empirically. His pen name is Less Wrong, and he has done this through, of all things, a Harry Potter fanfiction called Harry Potter and the Methods of Rationality. In particular, I want to quote something from the author’s profile page:
The Rule of Rationalist Fiction states that rationality is not magic; being rational does not require magical potential or royal bloodlines or even amazing gadgets, and the principles of rationality work for understandable reasons. A rationalist!hero should excel by thinking – moreover, thinking in understandable patterns that readers can, in principle, adopt for themselves. As opposed to the hero just being a born “genius” who comes up with amazing gadgets through an opaque discovery process, or who pulls off incredibly complicated gambits that would fail miserably if the reader tried something similar in real life.
This is something that, as someone who is every centimeter a rationalist, I wish were in more works of fiction. As much as I enjoy watching some of the popular Smart People in today’s media, such as House, they are at best incomplete representations of the process of analyzing a system or situation and deducing or inducing intelligent observations. What they don’t show, and what this fanfic does, is the grunt work of being smart. That sounds like a contradiction, but absolutely crucial to the process is a laborious laying of mental foundations that shore the mind against a set of errors in thinking to which human beings are particularly prone. One must continuously re-construct and re-interpret everything against a list of checks and balances to make the best possible attempt to both avoid overlooking some potentially significant piece of information, and to avoid assigning too much or an inappropriate significance to some piece of evidence.
Here I am unpacking all of this for you. The real clincher is that almost all of this happens subconsciously, once a person has enough practice/experience/training in thinking along rationalist lines. That makes it very difficult to explain, because most of us rely on some kind of subconscious upgrade, an Intuition 2.0, if you will, to get this done. Which brings me back to Less Wrong: he is elucidating these processes with fantastic clarity. If you want to know how to think in accordance with reality, read what he writes.
The Physics of Cracking Skulls March 2, 2011
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Gruesome, no? But these are the important questions of our times. And thankfully a team of intrepid forensic pathologists (and one physicist!) have stepped forward to bring us this study: Are full or empty beer bottles sturdier and does their fracture-threshold suffice to break the human skull?
Goodness, even the title is a little hard to wrap one’s head around. Throw in the first sentence of the introduction: “The examination of living or deceased victims of bar fights is not uncommon in routine forensic practice.” – and we can see we’re off to a rollicking good start. You’ll need institutional access or some other subscription to see the article, but fear not, I intend to explain the basics of the research here.
First, the results are described in terms of “impact energy”, at 30 Joules and 40 Joules for full and empty beer bottles respectively. A Joule is a unit of energy. For comparison, 35 Joules is about enough energy to lift a newborn baby up to a height of one meter. Let’s say we have an exactly 8 lb baby. If you have 30 Joules, you can lift that baby 0.84 meters. If you have 40 Joules, you can lift that baby 1.12 meters. So we’re dealing with a small, but not insignificant energy difference here, at least as far as our arms and lifting things are concerned. Now let’s put little Julianna down and pick up some beer bottles instead.
In the experiment, the researchers measured the energy difference needed to break a bottle by dropping a 1 kg steel ball on the bottles from various heights. They then already knew how much energy would be imparted to each bottle during the impact. How? What arcane powers of divination provided them with this knowledge? The answer is gravitational potential energy. Just by lifting the steel ball to a position further away from the center of the earth, the ball acquires potential energy – energy that manifests as the ball’s potential to fall down. The higher up the ball is when it falls, the harder it hits.
Now, to the results – you might think it would be easier to break an empty bottle over someone’s head compared to a full one, but you’d be wrong. In one of the most memorable phrases I’ve ever seen in a paper, the authors explain: “beer is an almost incompressible fluid.” That means that the shock of the impact in a full bottle gets transferred straight through to the opposite glass wall with almost no dispersion or degradation. Boom! Cracked bottle. By contrast, in an empty bottle, the stress and strain of the collision is transmitted throughout the bottle’s structure. This makes a full bottle more dangerous in a fight – when it cracks, it can cause severe cuts and lacerations. Of course, as the authors note, either one is sufficient to cause cranial trauma and is just generally a bad idea.
That about does it for beer bottles. I suggest you all go drink one instead of swinging one.
Neutrinos and the Human Body June 28, 2010
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So, some of the other grad students and I were discussing something or other about neutrinos. I don’t remember exactly what prompted it, but I proposed the question: How likely is it for a human body to register the presence of a neutrino during an average 70 year lifespan? Before I get into telling you guys about the answer, I should explain why the question is of any interest whatsoever.
Ever since the idea of neutrinos, tiny weakly-interacting electrically neutral particles, was proposed by a guy named Wolfgang Pauli on Dec 4, 1930, neutrino detection has been a matter of volume. The largest detector in the biz, Super-Kamiokande, contains 50000 tons of pure water, and registers about 5000 neutrino detections per year. That should stagger you. Consider that uncounted millions of neutrinos pass through every gallon of empty space every single second of every single day. And yet it takes the biggest structures mankind can muster to record just a few of the interactions. This is because interactions, on the level of fundamental particles, between neutrinos and ordinary atoms are exceedingly rare. Thus the question of human bodies as neutrino detectors acquires at least the status of a curiosity worth spending a few hundred words analyzing.
Now, down to business. According to Wolfram Alpha, 50000 tons of pure water has a volume of about 750,000 human bodies. Human bodies are, let’s be honest here, mostly water. So it’s not a stretch to say that it takes 750,000 of us to interact with 5000 neutrinos per year. A quick division gets us 150 humans interacting with one neutrino per year. Each and every one of us has a 1/150 chance of physically interacting with one of the 2×10^20 neutrinos that pass through our bodies every year. Postulating a 70 year lifespan, we all of us have slightly less than even odds on becoming a living neutrino detector for just one neutrino sometime within our lives.
So what happens if you’re one of the lucky ones? Not a whole lot. At this point, things start to depend on how much energy the neutrino has. But we can still draw some general conclusions. Without getting into the details of the various possible reactions, one thing you would absolutely get is an energetic electron or five. Depending on what the neutrino hits, you might also get a sudden episode of alchemy – a carbon atom changing to a nitrogen isotope, for example. More electrons would result when it decays back to carbon. And all of these things would be throwing out light rays. What does this mean for you, the consumer? Very little. Depending on where this happens, you might end up with a single broken molecule. Such detritus is routinely cleaned out by cellular processes. But, if you’re really unlucky, that broken molecule could cause a mutation in the DNA of one of your cells. If you’re really really unlucky, the mutation could be in an activated gene, which might cause that cell to die. Maybe you should look into some cellular insurance. I’m sure they have a neutrino clause in the policy.
Science and Death June 23, 2010
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Written June 21, 2010.
Today is Monday, and today I have to go to a funeral. To a scientist, in some ways, death is both more and less permanent. There is no empirical justification as yet for any kind of afterlife, and so we lose the comforting notion that the mind, soul, or other consciousness of a loved one continues to be a part of our world or of any other. Ashes to ashes, dust to dust, in the truest and most literal sense of the expression. A human being, according to my own amalgamation of the ideas of several scientific disciplines, is a highly energetic mass of complex molecules undergoing a continual and continually changing set of intricate regulatory processes enabling it to absorb oxygen, nutrients, and information and interact with other human beings to survive, reproduce, and thrive. To those of who object “Is that all?” I suggest that they underestimate the complexity of those molecules and their regulatory processes.
So what happens when a human being dies? These days death is defined by Western medicine as irreversible loss of electrical activity in the brain. Aside from a few difficulties with taking the relevant measurements, this is a perfectly serviceable definition. But it’s only the beginning of the process. What really gets us happens on the cellular level. Without the larger-scale processes like breathing, individual cells (those marvelous factories for proteins and energy) simply shut down. The bakery cannot make any cakes if it does not get any flour. The bakers lose their jobs, the building falls into disrepair and eventually falls apart. Thus it is with the cell. Of course, there the analogy fails, because bakeries are not continually fending off an invading army of decomposer bacteria. Without the active defense of the immune system (in all its multifarious glory), everything can eat us. This is why corpses stink. It’s not all your pent-up farts finally escaping, it’s the farts of the bacteria as they chow down on your femurs. Death is a disgusting business. Dying with dignity, or glory, is just not possible. You break down, you decay, you rot. You are eaten, digested, and absorbed. Nothing of what you were remains.
Or does it?
Those brutally hungry bacteria may efficiently disassemble your large scale structures, but your molecules mostly remain intact. Your atoms almost certainly so. Are you destroyed, or are you merely disseminated? There is some weight, and some lingering comfort, in this viewpoint. In a deep sense of the word, what you were remains. Now no longer part of a single human body, what you were disperses, joining other molecules from other lost loved ones to feed a bird, or roll along in an ocean wave. This is the conservation of matter and energy at its most personal, at its most touching. Nothing ever really dies, nothing is ever truly lost. Everything is reduced, recycled, reused, and reincarnated. Even those of us who are still alive are made of the remains of those past. The same molecules that made Caesar, Cleopatra, Aristotle, and Joan of Arc are us today. And it goes further than that – before that, the atoms that make those molecules were part of incomprehensibly massive stars that exploded with astronomical force to produce the substances that formed Earth and the rest of our solar system. When our system ends, out of the remaining gas clouds may form new stars, and the cycle will begin once more.
Ashes to ashes, dust to dust.
Pardon Our Construction April 2, 2010
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So, some of you loyal readers may have been wondering where Science In Real Life has been lately. To you I offer my apologies – the formats in which I have attempted to write this blog, while fun and educational, have ultimately proven unsustainable for reasons peculiar to my own foibles. However, all hope is not lost. I have a new idea for a more natural way to communicate the scientific thinking that goes on in my head, one that is in some ways truer to the original stated mission of this blog. Over the next few weeks I will be testing this idea, and if all goes well you will start seeing new entries, in a looser and more fluid format. Until then, happy sciencing.
