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What were the first technologie to be based on SR and GR?

  1. Feb 8, 2012 #1
    I'm not sure if this is the correct place for this as it is not about relativity as a topic in physics but the history of Einstien's theories.

    Both SR and GR were verified (or, more properly, not falsified) by experiment relatively (pun intended, I guess) soon after the theories were published. However, I am not aware of any technologies that were based on SR and GR before the GPS system or nuclear weapons.

    Does anyone know of any earlier technologies?
    Last edited: Feb 8, 2012
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  3. Feb 8, 2012 #2


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    No. But the reverse has happened. The invention of radar in the 1940's led Herman Bondi to invent the k-calculus which expresses relativity in terms of radar measurements.
  4. Feb 8, 2012 #3


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    Precision distance and time measurement were probably the first technologies where SR and GR effects were important experimentally. Though obviously you don't need SR and GR to measure time or distance, and both of these have a long, long, history.

    Distance measuring, and SR, was probably first impacted. According to wiki, Michelson and Morely did the first interferometric measurment of the prototype meter bar in 1892 or 1893, with more measurments by Fabry and Perot in 1906. Now, you don't need special relativity to have the idea to use interferometric techniques to measure distance, but based on the theories of the time, it was thought that if you did use such techniques, measurements would be distorted by an "Ether wind". But when the magnitude of the expected distortion effect was measured, it came up to be zero.

    The Michelson-Morley null resut for the Ether wind this was probably the first indication of the need for relativity, which was proposed later in 1905 by Einstein.

    You don't need SR or GR to create a single atomic clock - but you do need to account for gravitational time dilation to set up an accurate, global time coordinate system (TAI time).

    According to wiki, atomic clocks were invented in 1949. In the late 70's two important decisions were made. In 1977, corrections to the networked atomic time based on altitude were incorporated into the TAI time standard. So, General Relativity became officially recognized as important in defining the coordinate time TAI time on this date by the need to adjust the rates of atomic clock by the altitude above sea level.

    Some other important events:

    in the 1960's, interferometric techniques replaced the old meter prototypes. THis was the first step in re-defining the speed of light as a constant. Basically the most precise distance measurements were based on interferometry at the time, it was known that thee was no "Ether wind". However, the speed of light was not precisely defined due to the fact that the frequency of the light wasn't known yet.

    In the 1970's, advances in frequency measurements resulted in the redefinition of the metre as being the distance light travels in a certan number of seconds. This resolved some ambiguties found to arise in the old system and clearly set up the basis for using light and interferometric measurements as a tool to do distance measurments, it being the best and most accurate way of carrying out this process.

    The speed of light at this point became something that went from being measured, to something that was so accurate and reliable that it became the basis of measurement.

    Wiki sources:
  5. Feb 8, 2012 #4


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    If you consider nuclear weapons to be based on relativity (presumably because it turns some mass m into an energy mc^2), then by the same logic a campfire is also based on relativity. The mass m which is converted to energy is smaller, but the principle is the same.
  6. Feb 8, 2012 #5
    That's more quantum mechanics since combustion is (almost?) exclusively the breaking and reforming of covalent bonds and the release of heat due to the difference in electron bond energies, while nuclear reactions are exclusive the disruption of the strong force and the release of heat due to the difference in nucleon binding energy
  7. Feb 8, 2012 #6


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    Of course what you say is true, but how is the connection to relativity any different? This was the original question.
  8. Feb 8, 2012 #7
    I answered it above. There is no mass difference between the reactants and products in combustion because the energy is all stored in covalent bonds which are completely a electromagnetic phenomenon, whereas there is mass loss in a nuclear reaction because the the binding energy of the mother nucleus is greater than the sum of the daughter nuclei due to the mass energy equivalence described in general relativity.
  9. Feb 9, 2012 #8


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    Of course there is a mass difference. E = mc^2. Always! So in any exothermic reaction, the mass of the reactants is greater than the mass of the products by the amount
    ΔE/c^2. It is true that in chemical reactions this mass difference is very small and therefore nearly impossible to measure, but it is there. The reason I brought it up in the first place is that yours is a very common misconception, namely that nuclear reactions are qualitatively different than chemical reactions because in nuclear reaction there is a loss of mass while in chemical reaction there is not. However, this is simply not true.
  10. Feb 13, 2012 #9

    Could you show me sample calculations of the mass difference from the free energy of formation and of the free energy of formation from the mass difference?

    I can't seem to get answers that are consistent.
  11. Feb 13, 2012 #10


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    I don't have any way to calculate it other than what I said. Since I believe in relativity, I believe that E=mc^2. So if energy is given off, the reactants must have lost an amount of mass equal to E/c^2. Admittedly this effect is very small in chemical reactions. For example, take hydrogen, which has an energy content of about 120 MJ/kg, or 120 kJ/g. If I burn 1g of hydrogen together with 32g of oxygen, this will liberate 120 kJ Joules of energy. The resulting product (H2O) will weigh slightly less than 33g, by an amount 120kJ/c^2 = 1.3*10^-16 g. Obviously this is immeasurably small, but the situation is qualitatively the same as nuclear reactions. It's just the effect is large enough to measure in nuclear reactions.
  12. Feb 14, 2012 #11
    Wouldn't a massive amount of astronomical techniques and observing technologies be based on Relativity? It seems like that was really what the theories were about. I see no way how we could measure distance among other astronomical properties without relativity.
  13. Feb 14, 2012 #12
    That is true. I was just wondering about what the first technology to apply the concepts of relativity was. :smile:
  14. Feb 15, 2012 #13

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    Fire? No way. We had the technology of fire down pat thousands of years prior to the development of special relativity.

    The atomic bomb? Not really. That's quantum mechanics, not relativity. The bomb was developed before quantum mechanics and special relativity were rectified.

    I would say that it is accelerators that accelerate particles to a significant fraction of the speed of light. The first particle accelerators didn't do that. Accelerators from the 1940s/1950s and later do. The developers of those high energy accelerators must account for relativistic effects or the accelerators won't work as advertised.
  15. Feb 17, 2012 #14
    Others have said the same thing, but there is a much greater mass difference between the products and reactants in a chemical reaction than can be accounted for by the free energy of reaction.
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