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Posts Tagged ‘quantum mechanics’

Interplanetary Communications

There have been numerous means of sending a message from point a to point b over the span of human existence, within the past couple centuries it has become possible to ask someone at point b what the weather is like without actually sending someone to physically deliver your missive. Naturally people have started to take the ability to receive an instantaneous response for granted and most science-fiction (and a few fantasy) authors have naturally incorporated it into their works, even including some form of “interplanetary internet” in some cases. Though sometimes they don’t think things through too much, making mistakes such as interstellar wi-fi, to prevent such errors why don’t we take a quick look at how communications may work across interplanetary and interstellar distances.

Electromagnetic Radiation

First off there’s the single most common medium of transmission since the mid-20th century, radio waves. Transmitters translate text, verbalization, or other forms of data into discrete or continuous pulses of electromagnetic radiation (aka light) with wavelengths ranging from 1 millimeter to 100 kilometers and frequencies of 300 GHz to 3 kHz and a receiver detects and re-translates the information sent. Their low frequency and long wavelengths mean that radio waves have very little energy compared to other forms of EM radiation (and most definitely cannot cause cancer) but can potentially carry information for light-years before losing coherence. However radio waves are limited to the speed of light, so any attempt at calling someone further out than a light-minute or two (for reference, the sun is about eight light-min from earth) is going to experience a considerable amount of lag as the time it takes the waves to travel to their destinations becomes noticeable. In addition signals sent using radio will become incoherent with distance, depending on the frequency, the absolute limit being one or two light-years.

Another common means of communication is concentrated pulses of visible light, usually along glass fiber-optic cables which shield the signals from interference by the atmosphere. This method allows for far superior data quality than radio but atmospheric gases or particles can block them easily, as can physical objects that radio waves can pass through. In the vacuum of outer space there is considerably less matter in any form that can block an optical signal, however, especially if the signal is transmitted in the form of a laser capable of maintaining integrity over great distances. Lasers are also less susceptible to jamming or disruption by solar flares. But there has to be a clear line-of-sight between the transmitter and receiver and even lasers spread out and become incoherent over interstellar distances.

The Internet

As for how the internet might cope with space travel, e-mail and social networks would still be possible, and probably the primary form of communication between planets, but instant messaging would no longer be “instant” and if you think AOL back in the 1990s took a long time to load webpages, you probably wouldn’t have the patience to try surfing the internet from Mars. In all likelihood deep space colonies would form their own separate internets, with unique web sites inaccessible on earth or any other fairly distant regions. Certain websites that may be determined to be “important” enough might set up localized servers that would receive updates from one another at specified intervals, but you’d have to wait several hours and most likely need a massive transmitter to look up any other sites based outside your local region of space.

Neutrinos

Neutrinos, those supposedly massless particles that don’t interact with most normal matter and instead pass right through it, gained some publicity a few months ago when readings by CERN supposedly indicated that they travel slightly faster than the speed of light. Those readings were determined to be an equipment failure (a disconnected wire) but another group of researchers managed to do something not quite as amazing with neutrinos, but still significant. They managed to use neutrinos to send a one-word message through 240 meters of solid rock. Granted, the transmission speed was very slow, only 1 bit/second, and it took a particle accelerator to send the message, but still the neutrinos experienced negligible interference from materials that would block radio or optical signals completely. They could be very useful for communicating for people deep underground or underwater, or on the other side of a planet or star even. Neutrino transmission would need to be very tight beams like lasers to compensate for the low transmission rate, but the advantages of a transmission medium that is near impossible to block are considerable. Of course, if someone managed to place a neutrino detector between the sender and the receiver they could read the message without anyone knowing.

Quantum Entanglement

One of the science “buzzwords” of the century is “quantum mechanics”, relating to the behaviors of subatomic particles. One thing that science-fiction authors have extrapolated from the various “weird” properties covered under quantum mechanics is the use of “entanglement” to send messages instantaneously over any distance. The idea is that when two particles are “entangled” at the quantum level they can be separated and whatever happens to one particle happens to the other one instantaneously. Somewhere along the line someone decided that that could allow communication faster than the speed of light. In addition to sending messages instantaneously a quantum entanglement communique would be impossible to intercept as it would be teleported to the receiver. The harsh reality is that the act of observing an entangled particle breaks the connection with the paired particle, attempting to send data with entangled particles would by necessity require observing them.

However, quantum entanglement can be used to encrypt messages sent by conventional (currently only dedicated fiber optic cables) means such that only those who possess one of two “keys” can interpret the data. By encoding a transmission in the form of quantum states of a particle one ensures that the very act of intercepting it would corrupt the data and alert the holders of the keys as to how much of the message was intercepted. And it actually has been done, some governments and companies who consider security worth the expense use quantum cryptography for their most secure data transmissions, the Swiss canton of Geneva used it to send national election ballot results to the capital in 2007 for example. There have also been experiments with sending quantum encrypted messages over radio as well, it seems likely that the technology will become more prevalent over the next few decades. Though of course it only works between two specialized devices that have to be physically transported to their working locations.

The Utterly Fantastic

Of course, even quantum-encrypted FTL neutrinos would take years to travel from one solar system to another, so many authors have turned to the farther fringes of science in order to maintain “instantaneous communication”. For example, tachyons which are highly hypothetical particles that travel faster than light and which most scientists don’t believe exist. Or if their universe allows physical travel through some sort of “hyperspace” they might send radio transmissions through that same dimension where the normal laws of physics don’t apply. Heck, you might even use mentally “bonded” telepaths, worked for Heinlein.

Slicing Through the Gordian Knot of Quantum Gravity: Alternatives to String Theory (Part 3 of 3)

Quantum mechanics is the physics of the smallest of things, while general relativity is the physics of the largest. Not surprisingly, many physicists have been obsessessed with finding a Theory of Everything (TOE) that encompasses both limits.

This has not been easy.

In previous posts I’ve written of the difficulties that arise in creating a coherent theory of quantum gravity, and how one popular approach, string theory, attempts to solve the problem. String theory is not a failure, but neither has it been the overwhelming success quantum mechanics and general relativity have been. In particular, string theory has in general failed to make verified predictions in fundamental particle physics. (NB: some of the mathematical techniques of string theory have been applied to other areas of physics, but this is not the same thing.)

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Quantum Gravity, Part 2: A Thread ( or String) Leading Out of the Maze?

A good public relations campaign can do wonders.

Science is empirical. If there is no experiment, no observation, then an idea is truly relegated to “it’s just a theory.” [1]

Yet, consider string theory, a mathematical exercise so intricate Einstein’s general relativity is easy in comparison, and with no experimental evidence backing it whatsoever.

In the popular imagination, however, string theory dominates modern physics. Popularizations of string theory have topped bestseller charts. Friends and neighbors ask me about string theory. Students tell me they want to be string theorists, even though they, along with most of the public, are unsure what string theory even is.

In this essay I’ll attempt to untangle string theory for you, explain what it’s good for, why there are such devoted proponents, and what the skeptics say. Read the rest of this entry »

The Knotty Problem of Quantum Gravity: Part 1

You may have been in this situation:

You have two friends, your two best friends, both witty, fun, and thoughtful. An hour or so spent with either one leaves your brain buzzing with new ideas and insights. “I gotta get these two together,” you think.

You arrange a dinner, but the evening is a disaster. Your friends are incompatible in ways so deep, so fundamental, they can barely stand to be in the same room.

Now imagine your friends are physics theories; and not just any theories, but the two most revolutionary theories of the twentieth century, explaining entire libraries of data, predicting new, mind-blowing phenomena. They are quantum mechanics and general relativity.

And they do not play nice with each other.

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The Limits of Knowledge, Part II: Precise Uncertainty

(Second in a series on the limits of knowledge; see the first post here.)

Of all branches of modern science, quantum mechanics is most seen as magic–either a nihilistic, quasi-Voldemortesque dark magic that needs to be overthrown, or else a wonderful wand that can be waved to justify anything, and I mean anything.

To be sure, Einstein’s relativity disquiets many people.  Without trustworthy, absolute clocks, who can boast about trains running on time?

But quantum mechanics is an order of magnitude stranger. The quantum world is fundamentally uncertain and fuzzy, with slippery wavefunctions leaping from one state to another. Even Einstein himself, who helped to father the field, hated it.

As I’ve written in an earlier post, many SF authors choose either to rebel and literally write quantum mechanics out of the equation, or to use quantum mechanics as a convenient justification for neato pseudo-scientific wish-fulfillment.

All of this is because of fundamental misunderstandings about quantum mechanics. Read the rest of this entry »

Science, Symbolism, and Quantum Mechanics in SF

“Science fiction” is a sprawling, untidy genre, wearing so many masks it resists easy definition.  Even the “science” in science fiction spans a vast range, from incoherent technobabble to barely disguised excuses for magic to tightly constructed hard SF to Nebula and Hugo award-winning stories in which science makes no appearance at all. (Indeed, some have suggested the unifying thread is not science but history: James Gunn’s “the literature of change,” Kim Stanley Robinson’s “the histories we cannot know,” and David Brin’s “speculative history.”)  Some of the roles science plays in SF include:

* Scientific and technological advances signal that the world can and has changed, that history is in motion. This is especially relevant to the “speculative history” lens on SF.

* Advanced science and technology provide and justify exotic settings and characters, for example in many SFnal movies such as Avatar and Star Wars.

* Science can provide key plot points. This is particularly true in “hard” SF, where characters use science to reason their way out of a problem. Larry Niven at the height of his powers was a key exemplar, launching stories such as “The Coldest Place” and “Neutron Star.”

* Even the hardest SF is not really about science and technology but about our response to science and technological change. An example is the movie Gattaca, which critiques the danger of seeing people only through the lens of genetics.

What I want to write about today, however, is how science provides powerful symbols for SF, and how the imagery of science can echo the theme of a story.  And as befits SF, I’ll focus on stories that draw from a branch of science which is highly mathematical but which, deep down, appears as irrational and unreasoning as the Monster from the Id: quantum mechanics.
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