Category Archives: Physics

Physics, Space

A Propulsion Method for Space Probes?

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Going somewhere?
Going somewhere?

Space is vast; our current fastest spacecraft will take tens of thousands of years to get to other stars.


So fundamental breakthroughs in physics will likely be needed before it is practical to send out our first interstellar probes.


Such breakthroughs are inherently unpredictable, but here’s a hint at how one might happen: a physicist has proposed using the Large Hadron Collider to experiment on a possible propulsion method that could accelerate objects to significant fractions of the speed of light, Tech Review reports.


Physicist Franklin Felber specifically notes that high speeds “can be achieved without generating the severe stresses that could damage a space vehicle or its occupants.”


Effects on humans might be irrelevant: such a method might first be applied to very small vehicles that would send data back from other stars.  Some have even proposed that tiny spacecraft could use nanotechnology to build themselves out at their destinations.


(Image courtesy Andres Rueda, Flickr — Creative Commons license)

Physics

Review: The Time Traveler’s Wife

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Movie released: 2009
Set: 1960s to present

Summary of future technologies / events

  • Technology: time travel
  • Likelihood: extremely low?
  • Time frame if it is to occur: 2030+

Approach to the future – exploration of single possibility

Ratings

  • Futurism rating — 2: limits itself to a rigorously logical but unscientific use of time travel
  • Entertainment rating — 8: not as good or as tense as the book, but captures (or at least borrows) some of its spirit
  • Plausibility — 2: verges on impossibility

Time travel
Some reviews of this movie have been been off-base. The Washington Post reviewer wrote:

The mind may boggle at the inconsistencies and logistical impossibilities posed by all of Henry’s disappearances, and tampering with the past, and his crisscrossing travels with his alternate selves. Einstein and H.G. Wells would have a few problems with this movie. Nora Ephron, probably not.

In fact, the movie — following the lead of the book — takes an unusually rigorous approach to time travel. Inconsistencies and “logistical impossibilities” are absent. See this approving examination by physicist Dave Goldberg in Slate.

That said, it cannot be called “realistic,” for two reasons:

  • Biology — The minor reason is that, while we don’t know yet how to manipulate space-time in a way that would yield time travel, it is quite unlikely that a genetic mutation would lead to this ability. Genes interact with bodily processes, and haven’t shown signs of doing anything more. The super-mutation that Henry shows puts him in X-Men territory.
  • Philosophy — The larger reason that this story is unrealistic is that it takes an essentially pre-Copernican view of the universe, with people, and the Earth, as privileged and central. The time travelers in the story materialize in places (on the ground, not inside other objects, etc.) convenient to humans, suggesting that our matter is somehow distinct from other matter. Human emotions and memories guide their travels, again suggesting a kind of centrality. And the Earth itself acts as if it is a single place in the universe, despite all its diverse motions through space.
Physics

A cloaking device?

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Scientists have proposed plans for a kind of Star Trek-style cloaking device: materials that would bend light or other radiation around an area of space, effectively creating an invisibility shield.

The man-made materials are embedded with networks of exceptionally tiny metal wires and loops. The structures refract, or bend, different types of electromagnetic radiation—such as radar, microwaves, or visible light—in ways natural substances can’t.

The theory of metamaterials says that it would be difficult to detect that the light was ever bent around an object; there would not be disturbances revealing that something was being concealed.
Many obstacles stand in the way of practical application. For instance:

So far researchers have only developed metamaterials that divert radar and microwaves—rather than light waves, which are the key to invisibility. While that’s good news for Air Force generals who want to conceal warplanes, it’s bad news for wannabe wizards hoping for a magic cloak. Metamaterials that control visible light are particularly elusive in large part because the required matrix of metal loops and wires must be “nanosize,” or exceptionally small.

The Economist raises an objection on general principle:

Even if it ultimately proved possible to make an aeroplane completely invisible at all wavelengths, there would be a further problem. According to the laws of physics, an invisible person would necessarily be blind. In order to see light, the eye must absorb it, but in order for a person to be invisible, the body must not absorb any light. Thus, a spy plane could not be completely invisible if it were to be used for espionage or, indeed, flown at all, since its pilots would need to know its position relative to the ground.

More here in Book of Joe, especially the comment.