Okay, I know several people who have been waiting for me to get off my duff and talk about the speed of light.  This is Frank’s post, since he solved the riddle first Saturday.

To just blurt it out, the-speed-of-light-is-exactly-299,792,458-meters-per-second-in-a-vacuum.  That means that light will travel 299 million, 792 thousand, 458 meters in a second.  That’s about 300,000 kilometers per second, and about 186,000 miles per second.  The speed of light has been fixed with the increased accuracy of the definition and measurement of the meter.  The meter is defined as the distance light will travel in a vacuum in 1/299,792,458ths of a second.

Doesn’t that just give you goose bumps?  Take a look at this:

This is to scale. As you watch it, about 1.25 sec will pass as the little beam of light goes from the Earth to the Moon. That's how long it really takes.

To understand the speed of light, it might help to understand what exactly light is.  And what it is not.  I’m not going into the history of light, because I think everybody deserves to sit in college philosophy classes and suffer (I had to).  You go read Aristotle, I’ll read Einstein.  Believe it or not, there have been theories on the subject of light since the 6th century BCE.  As early as this the ancient Hindus were kicking around atomic theory.  By the 5th century BCE the Greeks were jumping in with some pretty interesting theories.  By 55 BCE, Lucretius (a Roman) wrote:

“The light & heat of the sun; these are composed of minute atoms which, when they are shoved off, lose no time in shooting right across the interspace of air in the direction imparted by the shove.” – On the nature of the Universe

Remember, this was 55 BCE.  There wasn’t anything even close to a telescope hanging around at the time.  This is also an interesting attempt to nail the concept of light down to the physical world, and get it out of the realm of religion.  Unfortunately, 55 BCE is believed to have been the year of Lucretius’s death (at the age of 43), so perhaps it didn’t work out so well for him.

Light exists as a wave-particle duality.  This isn’t really that special, because all matter is believed to exist in the same state of duality.  This whole concept is the foundation of quantum mechanics, and you’re just going to have to trust me here.  Just imagine a tiny little packet called a photon traveling through space as a wave, and you’re there.  That’s light.  What you “see” is only how your brain interprets the nerve impulses which have been fired by the photons.  You know that light exists much wider, deeper, and larger than we can see without some seriously expensive equipment.  Here is what you don’t see:

Light spectrum by Philip Ronan, all rights reserved.

There have been several good attempts to measure the speed of light through history.  In 1676 Danish Physicist Ole Romer used a telescope to watch the motions of Jupiter and Io, and calculated that it took 22 minutes for light to traverse the diameter of the orbit of the Earth.  Of course, nobody knew the size of the diameter of the orbit of the Earth.  If they had, Ole’s calculations would have set the speed of light at 227,000,000 m/s.  I have to say, that’s a pretty decent working hypothesis.

Several things are believed to be apart from the speed of light “speed limit”; most interestingly tachyons and quantum entanglements.  In the case of quantum entanglements, since you can’t pin down the exact position of a subatomic particle at any given moment, no information or mass is actually transmitted, therefore it doesn’t violate the speed limit (gotcha!).  Tachyons are tiny little critters, hypothetical really, that are limited to the space portion of the energy-momentum graph.  They can’t go slower than too fast, in other words.  They lose energy and cease to exist.

What you do see, by Ibrahim Lujaz, all rights reserved.

I’m sure as our knowledge of the universe around us increases, we’ll get a better understanding of light, it’s speed limit, and what is or is not bound to it.  I’ve been told that for every “law”, there is something which exists outside of it.  Thanks, Frank.

What pairs well with chocolate? A pricey tablet computer, of course.

Stefan Magdalinski debated what to get for his sweetheart for her June birthday. Eventually, he decided on a candy Apple: He ordered his wife a chocolate-covered iPad.

As told on Magdalinski’s blog and reported by Mashable, what makes this feat more impressive is that he orchestrated the gift’s shipment from the U.K. to South Africa, calling two friends at a British chocolatier with an unusual question:

“Could you freeze an iPad in chocolate carbonite, and have it survive?”

The proof is in the chocolate. A gift that involved both an interesting customs discussion and a very confused wife ended in sweet success. Magdalinski: “no iPads were harmed in this production.”

Counting your calories? Other iPad combinations might better fit your tastes. As described on the blog CrunchGear, nostalgic Apple-users have gutted older computers to give them a new, touchable face.

And for those that want to hearken back a bit further, the blog Gizmodo recently described another iPad vision almost as romantic as chocolates, an iPad typewriter.

Luckily, none of these combinations required blending.

Related content:
Discoblog: Will The iPad Blend? Watch and Find Out.
Discoblog:  iPad Arrives—Some Worship It, Some Critique It, HP Tries to Kill It
Discoblog: Hey Baby, Wanna Come Over and Try My New iPad?

Images: Ahead Robot / Stefan Magdalinski

OMFSM.

First, there’s going to be a remake of "Fright Night", an actually pretty good vampire flick from the 1980s. I’m generally opposed to most remakes, but I think that this isn’t such an awful idea, since the premise itself is a good one. However, the remake’s director is the same guy who did "Lars and the Real Girl", which was… well, I’ll just say I didn’t like it and leave it at that.

But…

Guess Who they tapped for the part of Vincent, the fey late-night movie host who winds up becoming a real vampire hunter? David Tennant!

Oh yeah. I’ll watch that. The original role was played by Roddy McDowall, who was great. Tennant is a pretty good fit to that role, too.

Given who played the original role, I wonder what’s next for Tennant after this? I’m thinking Cornelius in a "Planet of the Apes" sequel. Ook ook.

Knowing something like the back of your hand supposedly means that you’re very familiar with it. But it could just as well mean that you think it’s wider and shorter than it actually is. As it turns out, our hands aren’t as well known to us as we might imagine. According to Matthew Longo and Patrick Haggard from University College London, we store a mental model of our hands that helps us to know exactly where our limbs are in space. The trouble is that this model is massively distorted.

To keep track of where your various body parts are, your brain maps your posture by processing information from your muscles, joints and skin. Close your eyes and move around a bit, and you’ll still have a good idea of what position you’re in even if you can’t see or touch yourself. But there’s no such direct signal that tells your brain about the size and shape of your body parts. Instead, your brain stores a mental model with those dimensions mapped out.

To visualise this model, Longo and Haggard asked volunteers to hide their hand under a board and use a baton to indicate the position of ten landmarks – the tip and base knuckle of each finger. Their answers were surprisingly inaccurate.

They underestimated the lengths of their fingers by anywhere from around 5% for their thumb and over 35% for their ring and little fingers. In contrast, they overestimated the width of their hand by around 67%, and particularly the distance between their middle and ring knuckles. Our mental hand is a shorter, wider version of our real one. Longo and Haggard found the same thing if they asked the recruits to angle their hands at 90 degrees under the board, and if they tested the right hand as well as the left.

These distortions actually reflect how sensitive each part of the hand is. The skewed mental map is remarkably similar to another map called Penfield’s homunculus, which charts the areas of the brain’s somatosensory cortex (the bit that processes touch information) that is devoted to each body part. Regions that have a more acute sense of touch correspond to larger parts of the homunculus, but they also loom bigger in our mental map. Regions that are less sensitive are smaller on both charts.

As we move from the thumb to the little finger, our digits become less sensitive and the mental map increasingly underestimates their true size. The back of the hand is more sensitive to movement across it than movement along it; accordingly, our mental map depicts a wider, shorter hand.

And we have no idea about this. Consciously, the volunteers had a pretty good appreciation of the size and shape of their hands. When Longo and Haggard showed them a selection of hand images and asked them to select the one that best matched their own, they did so very accurately. But even though they passed this test, they still failed to place the baton in the right place when their hands were hidden.

If we hold such a distorted depiction of our own hands, how is it that we ever grasp things successfully? It’s possible that our motor system uses a different model but Longo and Haggard put forward two more plausible ideas: that cues from vision are strong enough to override the warped map; and that we learn to correct for the misshapen model. Only by removing both of these factors did they finally reveal how skewed our perceptions actually are.

Reference: PNAS http://dx.doi.org/10.1073/pnas.1003483107

Image: Hands by Toni Blay

More on perception:

• How our skin helps us to listen
• How wearing a cast affects sense of touch and brain activity
• Blind man navigates obstacle course perfectly with no visual awareness
• Pain in the eye of the beholder
• Brain treats tools as temporary body parts