The double slit experiment

There’s a nice little physicsworld article dating back to 2002. It was written by then-editor Peter Rodgers, and it started by asking “What is the most beautiful experiment in physics?” The answer was, of course, the double slit experiment, which was first performed by Thomas Young in 1801: Double slit experiment image from the curiosity makes you smarter article by Ashley Hamer People refer to the double slit experiment as an example of the weirdness of quantum physics. Or to promote weird ideas such as the…

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Quantum computing and the quantum quacks

I have a computer science degree. I work in IT, and have done so for many years. In that period "classical" computers have advanced by leaps and bounds. I remember teletypes and paper tape, and punched cards too. I also remember when a top-notch disk drive was the size of a washing machine and the cost of a car. It provided a miserly 10 megabytes of storage. My disk drive today is the size of my wallet and cost £46.99. It provides a terabyte of storage.…

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Quantum gravity is a castle in the air

When you spend some time digging into the history of physics, you find yourself uncovering the foundations of physics, and then you come to appreciate a few things. You come to appreciate how gravity works, and why an electron falls down. It isn’t because gravitons are flying back and forth: Graviton image by Julie Peasley, see http://www.particlezoo.net/ You also come to appreciate that light interacts with light to form electrons and positrons in gamma-gamma pair production. You come to appreciate that the electron is not a…

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What energy is

If you ask what is energy? some people will tell you that energy is an abstract thing. This was how Richard Feynman described it in the Feynman lectures, volume I chapter 4. He used the analogy of children’s blocks. He said these blocks were absolutely indestructible and could not be divided. But then he said there are no blocks. Only then he contradicted himself by saying energy has a number of different forms, such as gravitational energy, kinetic energy, and heat energy: Image from Assignment point…

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The fate of the universe

One of the things cosmologists like to talk about is the fate of the universe. Some say it all depends on the density parameter omega: Ω. This started life as the average matter density of the universe divided by a “critical” matter density for the Friedmann universe: Based on the Friedmann universes public domain image by BenRG, see Wikipedia Commons and Wikipedia Nowadays when we talk about omega we don’t restrict ourselves to matter alone. That’s because energy doesn’t necessarily take the form of matter, and…

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The edge of the universe

When you dig into the history of cosmology, some things catch your eye. Things like the “boundary conditions” in Einstein’s 1917 cosmological considerations in the general theory of relativity. Or something Willem de Sitter said in his 1917 paper On the relativity of inertia. Remarks concerning Einstein's latest hypothesis. He said this: “if the gμν at infinity are zero of a sufficiently high order, then the universe is finite in natural measure”. There’s also something Paul Steinhardt said in his 1982 Natural Inflation paper. He said this:…

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Dark energy

Dark energy is said to be a mystery. Google on dark energy mystery and you can find plenty of material saying as much. Such as dark energy: the biggest mystery in the universe by Richard Panek in the Smithsonian magazine. Or dark energy: mystery of the millennium by Thanu Padmanabhan on the arXiv. Dark energy comes above dark matter in 10 greatest unsolved mysteries in physics on IFL science, and since it’s circa 68% of the mass-energy of the universe as opposed to 27% for dark…

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Inflation

The theory of cosmic or cosmological inflation is related to Big Bang theory. It’s been around now for the thick end of forty years. Or more. By 1980 a lot of cosmologists were happy that the universe was expanding, and that it wasn’t a steady-state universe. A lot of cosmologists also thought of the initial expansion of the universe as something fairly steady. However inflation introduced the idea that the initial expansion was very rapid: Image from Rod Nave’s hyperphysics As for how it all began,…

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The Big Bang

Big Bang cosmology arguably started in 1917. Vesto Slipher had measured 21 galactic redshifts by 1917. That’s when Albert Einstein wrote his cosmological considerations paper and Willem de Sitter came up with the de Sitter universe. The next year in 1918 Erwin Schrödinger came up with his cosmic pressure. In 1922 Alexander Friedmann came up with a non-static universe. In 1924 he came up with negative and positive curvature, and Knut Lundmark came up with an expansion rate within 1% of measurements today. In 1927 Georges…

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A compressed prehistory of dark energy

In the Wikipedia dark energy article you can read how the term "dark energy" was coined by Michael Turner in 1998. This was in a paper co-authored with Dragan Huterer called prospects for probing the dark energy via supernova distance measurements. It referred to the type 1a supernovae observations made by the Supernova Cosmology Project and by the High-Z Supernova Search Team. Their observations indicated that the expansion of the universe is accelerating, which was contrary to expectations and led to Nobel prizes in 2011: Expanding…

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