Dark Matter

Dark matter occupies about 23% of the known Universe. It does not emit or reflect radiation, making it somewhat undetectable, since it cannot be ‘seen’ with any equipment. However, it is affected by gravity, but not in the same way as normal matter. It is believed that dark matter is made up of a new subatomic particle, but nobody knows what that is either. In fact, nobody even knows whether dark matter even exists or not, it is simply one of the many ways to account for the ‘missing mass’ that hasn’t been accounted for in the Universe.

Evidence of this anomalous dark matter is not unnoticed though, as it has a visible gravitational lensing effect on galaxy clusters, such as the Bullet Cluster in the image above. Gravitational lensing happens when a large mass passes between an object and the Earth. The light from the object is bent by the gravitational effects of the mass, causing an ‘image’ of the object to be seen elsewhere. It looks a bit like this .

Since all my followers are fantastic at doing what I’m doing… How do I do this with trig identities?

Something interestingly irrelevant: The Rapunzel Number

Physicists from the University of Cambridge has recently quantified the curliness of hair and developed a theory used to predict the shape of a ponytail.

“To derive the Ponytail Shape Equation, the scientists took account of the stiffness of the hairs, the effects of gravity and the presence of the random curliness or waviness that is ubiquitous in human hair. Together with a new quantity described in the article – the Rapunzel Number –  the equation can, they say, be used to predict the shape of any ponytail.”

Superconductors.

The basic concept of a superconductor is that it is capable of sustaining an electrical current without resistance. Resistance in a circuit is what causes a loss of energy, so superconductors are the closest thing we have to perpetual motion. However, they only work at near absolute zero, or more specifically, anything colder than 91 Kelvin. 

When a superconductor is cooled to these temperatures, any interaction with a magnet causes a repulsion, this effect is called the Meissner Effect. The induced field in the superconductor opposes the applied field of the magnet, therefore repelling each other. So if the two repel, how is it possible to achieve any levitation? When the magnet is moved closer the flux trapping effect is engaged and the superconductor not only repels the magnet, but attracts it as well. The magnetic flux lines from the magnet are trapped inside the superconductor causing the magnet to be held at a fixed position. This is only possible if there are imperfections in the crystalline structure of the superconductor.

Of course, the opposite effect of levitation also occurs. When the magnet is picked up, the superconductor remains in magnetic suspension, and hovers below the magnet. Another phenomena is that the levitated magnet will freely move at a fixed distance over the superconductor without friction, so the applications would benefit transport, which means we can all have hover cars now.

Glowsticks; how do they work?

The emission of light is the only physics principle involved here, but the chemistry isn’t that hard to understand the basis of. Glowsticks work by mixing two compounds, typically hydrogen peroxide and a phenyl oxalate ester. The hydrogen peroxide is kept in a separate glass tube, which is broken when the glowstick is bent. The ester is then oxidized by the hydrogen peroxide, which creates a chemical called phenol and an unstable peroxyacid ester. That peroxyacid ester decomposed and additional phenol is released amongst a cyclic peroxy compound, which decomposes into carbon dioxide. This decompostion releases a substantial amount of energy, which is not observed without the presence of a fluorescent dye. Moving on.

The dye is the component capable of chemiluminescence, which is why light is not emitted without it. When the energy from the decomposing cyclic peroxy compound is transferred to the dye, the electrons are temporarily excited into a higher energy level and when they eventually fall back to the ground state, the loss of energy of the electron is released as a photon. The colour, or frequency of this photon depends on how much energy it is released with. The higher the energy, the further toward the violet end of the spectrum the light emitted will be. Different dyes rely on different amounts of energy to excite electrons, which is why other frequencies are emitted. 

The speed and intensity of the reaction is dependent on the chemicals used, but also the temperature. Putting a glowstick in the freezer slows the atoms’ collisions down, therefore releasing less energy over the same amount of time which causes less photons to be emitted. However, the reaction lasts a lot longer. The opposite is true for higher temperatures, where the light is brighter, but the glowstick won’t last as long. In conclusion, glowsticks are really cool.

Polarised Light

Light is an electromagnetic wave that travels through space. If you were to consider a transverse wave, from side on, most look like a sine curve, which travel along and vibrate up and down, quite like waves in the ocean. However, the electromagnetic radiation produced by the sun vibrates along many planes, more simply with a vertical and horizontal component. The vertical are the up and down waves, where as the horizontal are left and right waves. This is unpolarised light.

To polarise light is to remove either the horizontal or vertical component of the wave, this is most easily done by filtering. If unpolarised light was shone through a vertical slit, this would eliminate any horizontal component. If that polarised light produced was directed at a horizontal slit, it wouldn’t produce any light due to having blocked the vertical component. The way polarised sunglasses work is the same, they have very thin, vertical slits which block out the horizontal vibration that causes glare. 

As for this neat picture I found, it was done similarly. Ice was placed between two polarisation filters, and when the polarised light reflected from the ice, two rays were produced at right angles, one slower from the other. These rays interfered with each other, making all the pretty colours. 

Mass Energy Equivalence 

The idea of mass-energy is due to Einstein’s famous equation E=mc², which indicates that if the mass of a nucleus decreases, the energy must increase, since the speed of light is constant. If the energy were to decrease, we would expect a heavier mass.

Mass-energy somewhat explains the release of energy during a nuclear fission or fusion reaction. Nuclei are made up of protons and neutrons, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons. The difference is a measure of the nuclear binding energy which holds the nucleus together. As an example, in Uranium-235 fission, a slow neutron is captured by the nucleus, making it unstable. The products of the reaction include Krypton-89 and Barium-144 + 3 neutrons. The combined mass of the products will be less than the original mass of the Uranium. This loss of mass is called a mass deficit (∆m) and the mass deficit is what releases the energy in a reaction, since mass and energy are equivalent. This energy is calculated by E=∆mc².