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The physics of organisms........

Discussion in 'Redox Rx' started by Jack Kruse, Jun 27, 2021.

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  1. Jack Kruse

    Jack Kruse Administrator

    Although Newtonian mechanics gives an excellent description of Nature, it is not universally valid. It was good enough to get man to the moon but could not explain the perihelion of Mercury. When we reach extreme conditions — the very small, the very heavy, or the very fast — the Newtonian Universe that we’re used to needing replacing. You could say that Newtonian mechanics encapsulates our common-sense view of the world. One of the major themes of twentieth-century physics is that when you look away from our everyday world, common sense is not much use.

    The first thing to say is that the speed of light is fast. Really fast. The speed of sound is around 300 ms^-1; escape velocity from the Earth is around 10^4 ms^-1; the orbital speed of our solar system in the Milky Way galaxy is around 10^5 ms^-1. Nothing travels faster than light.

    1. The principle of relativity: the laws of physics are the same in all inertial frames

    2. The speed of light in vacuum is the same in all inertial frames

    On the face of it, the second postulate looks nonsensical. How can the speed of light look the same in all inertial frames? If light travels towards me at speed c and I run away from the light at speed v, surely I measure the speed of light as c-v. Right? Well, no. Why?

    Time ticks at different rates for observers sitting in different inertial frames = relativity
     
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  2. Jack Kruse

    Jack Kruse Administrator

    The first evidence that light does not travel instantaneously was presented by the Danish astronomer Ole Rømer in 1676. He noticed that the periods of the orbits of Io, the innermost moon of Jupiter, are not constant. When the Earth is moving towards Jupiter, the orbits are a few minutes shorter; when the Earth moves away, the orbits are longer by the same amount. Rømer correctly deduced that this was due to the finite speed of light and gave a rough estimate for the value of c. This was the first time in history the speed of light was deduced

    By the mid-1800s, the speed of light had been determined fairly accurately using experiments involving rotating mirrors. Then came a theoretical bombshell. Maxwell showed that light could be understood as oscillations of the electric and magnetic fields. He related the speed of light to two constants, e0 and μ0, the permittivity and permeability of free space, that arise in the theory of electromagnetism
    But, as we have seen, Newtonian physics tells us that speeds are relative.

    If Maxwell’s equations predict a value for the speed of light, it was thought that these equations must be valid only in a preferred reference frame. Moreover, this does not seem unreasonable; if light is a wave then surely there is something waving. Just as water waves need water, and sound waves need air, so it was thought that light waves need a material to propagate in. This material was dubbed the luminiferous ether and it was thought that Maxwell’s equations must only be valid in the frame at rest with respect to this ether.

    In 1881, Michelson and Morley performed an experiment to detect the relative motion of the Earth through the ether. Since the Earth is orbiting the Sun at a speed of 3 x 10^4 ms-1, even if it happens to be stationary with respect to the ether at some point, six months later this can no longer be the case.

    Towards the end of the 1800s, the null result of the Michelson-Morley experiment had become one of the major problems in theoretical physics. Several explanations were proposed, including the idea that the ether was somehow dragged along with the Earth. The Dutch physicist, Hendrik Lorentz, went some way to finding the correct solution. He had noticed that Maxwell’s equations had the peculiar symmetry that we now call the Lorentz transformations in mathematics.

    Although Lorentz had put in place much of the mathematics, the real insight came from Einstein in 1905. He understood that there is no mechanical mechanism underlying the Lorentz transformations. Nor is there an ether. Instead, the Lorentz transformations are a property of space and time themselves.

    With Einstein’s new take on the principle of relativity, all problems with Maxwell’s equation evaporate. There is no preferred inertial frame. Instead, Maxwell’s equations work equally well in all inertial frames. However, they are not invariant under the older transformations of Galilean relativity; instead they are the first law of physics to be invariant under the correct transformations of Einstein/Lorentz relativity.
     
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  3. Jack Kruse

    Jack Kruse Administrator

    The crazy part of Einstein's relativity is that if cause and effect are true it means traveling faster than the speed of light also must be true

    The converse to this is that if we do ever see particles that travel faster than the speed of light, we’re in trouble. We could use them to transmit information faster than light. But another observer would view this as transmitting information backwards in time. All our ideas of cause and effect will be turned on their head.
     
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