Watch zebrafish cells chase each other into patterns!

An amazing article from Ed Yong describes a new mechanism for pattern formation:

Coloured Cells Chase Each Other To Make A Fish’s Stripes

Zebrafish patterns aren’t just controlled by a chemical reaction-diffusion mechanism — the pigment cells actually chase each other! The different color cells sort themselves into stripes, spots, or other patterns depending on their relative speeds.

fuckyeahfluiddynamics:

In the ocean, many forces compete in driving convection, including the temperature and salinity of the water. In the laboratory, it’s possible to mimic these characteristics of oceanic circulation using two different fluids driven by temperature and concentration differences. Recently, researchers were exploring this problem—with the added twist of tilting the fluids ~1 degree—when they discovered a surprising result. After an extended time, the convection self-organized into alternating parallel columns of ascending (dark) and descending (light) fluid. The researchers nicknamed this behavior super-highway convection. Read more about it here or in their paper. (Video credit: F. Croccolo et al; submitted by A. Vailati)

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An electromagnetic wave bootstraps itself through the void

Image 1: Source: Wikipedia article on “Electromagnetic radiation” (image source; cc-by-sa)

Caption: “Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D diagram shows a plane linearly polarized wave propagating from left to right.”

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Image 2: Source: Wikipedia article on “Electromagnetic radiation” (image source; cc-by-sa)

Caption: “This 3D diagram shows a plane linearly polarized wave propagating from left to right. Note that the electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together.”

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Image 3: Source: Wikipedia article on “Electromagnetic radiation” (image source; cc-by-sa)

Caption: “The electromagnetic waves that compose electromagnetic radiation can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This diagram shows a plane linearly polarized EMR wave propagating from left to right. The electric field is in a vertical plane and the magnetic field in a horizontal plane. The two types of fields in EMR waves are always in phase with each other with a fixed ratio of electric to magnetic field intensity.”

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If compression waves, like sound, need to travel through a carrier medium, then how can electromagnetic waves propagate themselves through empty space?


A photon acts a little like the Glider in Conway’s Game of Life: at each step, it creates the conditions for the next step. Now, this is just one way of viewing an electromagnetic wave, and far from complete. But it’s interesting to think about!

More quotes from Wikipedia:

“Similar to the way that a changing magnetic field generates an electric field, a changing electric field generates a magnetic field. This fact is known as Maxwell’s correction to Ampère’s law. Maxwell’s correction to Ampère’s Law bootstrap together with Faraday’s law of induction to form electromagnetic waves, such as light. Thus, a changing electric field generates a changing magnetic field, which generates a changing electric field again.”

(Source: Wikipedia article on “Magnetic field”)

“A common misconception is that the E and B fields in electromagnetic radiation are out of phase because a change in one produces the other, and this would produce a phase difference between them as sinusoidal functions (as indeed happens in electromagnetic induction, and in the near-field close to antennas). However, in the far-field EM radiation which is described by the two source-free Maxwell curl operator equations, a more correct description is that a time-change in one type of field is proportional to a space-change in the other. These derivatives require that the E and B fields in EMR are in-phase (see math section below).”

(Source: Wikipedia article on “Electromagnetic radiation”)

And it gets weirder: 

According to the special theory of relativity, the partition of the electromagnetic force into separate electric and magnetic components is not fundamental, but varies with the observational frame of reference: An electric force perceived by one observer may be perceived by another (in a different frame of reference) as a magnetic force, or a mixture of electric and magnetic forces.

Formally, special relativity combines the electric and magnetic fields into a rank-2 tensor, called the electromagnetic tensor. Changing reference frames mixes these components. This is analogous to the way that special relativity mixes space and time into spacetime, and mass, momentum and energy into four-momentum.”

(Source: Wikipedia article on “Magnetic field”)

In the end, we are self-perceiving, self-inventing, locked-in mirages that are little miracles of self-reference.

I offer the modest proposal that our Universe is simply one of those things which happen from time to time.

Quote in context: “If it is true that our Universe has a zero net value for all conserved quantities, then it may simply be a fluctuation of the vacuum, the vacuum of some larger space in which our Universe is imbedded. In answer to the question of why it happened, I offer the modest proposal that our Universe is simply one of those things which happen from time to time.”  

– Tryon, E.P., 1973. Is the Universe a Vacuum Fluctuation? Nature, 246(5433), 396-397. doi:10.1038/246396a0

http://www.nature.com/nature/journal/v246/n5433/abs/246396a0.html

http://en.wikipedia.org/wiki/Vacuum_genesis