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Thread: space race

  1. #1 space race 
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    which moves fastest: gamma rays, visible light, or radio waves or do they all move at the same speed? they say speed of light but is it just the speed of the EMS?


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  3. #2  
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    yeh all at the same speed. which is the same as the speed of light.
    notice that visible light is part of the ems


    everything is mathematical.
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  4. #3  
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    In vacuum they all have the same speed. In a transparent medium, such as air or glass, most of the time they have different speeds. The same medium is not transparent for the entire spectrum though, a large part of wavelengths is absorbed or reflected.
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  5. #4 Re: space race 
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    Quote Originally Posted by Darth Lord Sidious
    which moves fastest: gamma rays, visible light, or radio waves or do they all move at the same speed? they say speed of light but is it just the speed of the EMS?
    It is the speed of light in a vacuum that is constant. All photons move at the same speed, denoted c, in a vacuum, independent of the inertial reference frame.

    In a medium the situation is more complicated. Photons still move at c, but the process of transmission involves many absorptions and re-emissions. Photons move between atoms being alternately absorbed, raising electron energies which then fall re-emitting photons. That process takes a little bit of time. The result is an effective speed that is somwhat slower, the ratio with the speed in a vacuum being the index of refraction. The speed of the process varies with the energy of the photon, which is inversely proportional to wavelength.

    There is an alternate classical description of the process of transmission of electromagnetic waves in a material, but the result is the same, a slightly slower speed for light. It is reflected in the variation of electric permeability and magnetic susceptibility in a material from the vacuum values. the result is the same -- a slight slower speed of propagation in a material.

    By EMS is think you mean electromagnetic spectrum. It is not clear to me what you mean by the speed of the EMS. Photons move at c. The EMS is nothing but a categorization of photons in terms of wavelength, a menu or a mathematical construct depending on your point of view. In reality it is a dictionary pairing names with ranges of wavelength. It is not a physical thing, and so does not move.
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  6. #5  
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    So a transparent material is a substance that continually re-emits light while for the most part (dependent on the index of refraction) preserving its original trajectory? Does any of the light make it through without ever being absorbed? Is this just a model or has it been proven to any extent?
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

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  7. #6 Re: space race 
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    Quote Originally Posted by DrRocket
    It is the speed of light in a vacuum that is constant. All photons move at the same speed, denoted c, in a vacuum, independent of the inertial reference frame.
    Wrong! The term is 'Free Space vacuum' ie free of all other influences, including gravity and magnetic fields. Yeah I know it's pedantic, but science is a precise subject.
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  8. #7  
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    Does gravity effect various wavelengths differently?

    Of course there is the interstellar medium...which not only has an effect on the light as you would expect, but also causes Faraday rotation due to the induced ionization caused by passing particles, and by the magnetic fields surrounding various entities. Astrophysicists actually seem to use this property to measure the magnetic fields of anything they want.

    "In the case of radio pulsars, the dispersion caused by these electrons results in a time delay between pulses received at different wavelengths, which can be measured in terms of the electron column density, or dispersion measure. A measurement of both the dispersion measure and the rotation measure therefore yields the weighted mean of the magnetic field along the line of sight."
    http://en.wikipedia.org/wiki/Faraday_effect
    Of all the wonders in the universe, none is likely more fascinating and complicated than human nature.

    "Two things are infinite: the universe and human stupidity; and I'm not sure about the universe."

    "Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence"

    -Einstein

    http://boinc.berkeley.edu/download.php

    Use your computing strength for science!
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