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Space-time can mean without mater or energy ?

  1. Nov 27, 2012 #1
    Hello all .
    My questions are :
    Space/time are any meaning without matter or energy ?
    Space/time are exist without matter or energy ?
    We can image space/time without any matter or energy ?
    These terms are any meaning in physics ?
  2. jcsd
  3. Nov 27, 2012 #2

    Simon Bridge

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    You seem to be thinking of matter and energy as different things, so I think you need to describe what you mean by "energy" in this case before we can answer your question.
    All the terms you have used have meaning in physics.

    I'm guessing that the question you want to ask is difficult for you to put into English.
    Have another go - we can thrash it out together.
  4. Nov 28, 2012 #3


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    According to Einstein's Special Relativity, it takes a rigid ruler made out of matter to define space and it takes a clock made out of matter to define time and it takes light energy to define a spacetime coordinate system so without those, you would have to come up with some other definition of spacetime in order to give it any meaning, but that kind of speculation is not allowed on this forum.
  5. Nov 28, 2012 #4

    Simon Bridge

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    Technically - any reference points can constitute a "ruler" - need not be rigid or made of matter - and anything that makes time can be a clock - does not need to be matter. It's just nice to use objects that are handily available in the laboratory and don't change much over the lifetime of the experiment.
  6. Nov 28, 2012 #5
    I am not sure maybe different .
    A matter like electron it's not energy it has rest energy and Equivalent with energy .
    We can not consider a electron pure energy it's a elementary particle so they are different things .
    But my question is if all matter and energy destroyed or going to nothing ! space/time still exist or not ?
    English is not my first and even my second language :cry:
    I'm good in reading but trouble in writing

    Thank you .
    Last edited: Nov 28, 2012
  7. Nov 28, 2012 #6

    Simon Bridge

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    In fundamental physics we consider matter and energy to be the same thing - so an electron has rest-energy given in relation to it's rest mass by ##E=mc^2## ... the total energy of an electron would be ##E=\gamma mc^2## ... which would include rest-energy and kinetic energy. It also has various forms of potential energy in relation to different fields.

    Well - by the law of conservation of energy, this is not possible so it is difficult to imagine how one would do such an experiment to find out.

    In physics - space is the distance between things so the concept of "space" has no meaning without things to mark out it's extent. Similarly, "time" has no meaning without clocks.

    We can conceive of an infinite volume with only an ideal point observer in it ... but how does the observer know? There is nothing to see - no experiment that could be performed to discover the extent of space and time if it were to exist. Functionally ... there is no space or time. (Though someone may want to talk about vacuum fluctuations here.)

    I have heard of a bunch of models where the Universe comes from nothing and the energy in it comes, sort-of, as a side-effect of the expansion of space.
    Naturally the other way around as well ... clearly the ideas are tied up with each other somehow and may turn out to be different ways of looking at the same thing.

    I think, at a fundamental level, these questions are, at best, unresolved and at worst: meaningless... and we are in serious danger of philosophy.

    I know how you feel - I have bits of other languages and reading is easier than working out how to say things.
  8. Nov 28, 2012 #7
    I have still problem with that ,
    A apple is not only red or yellow it has other properties . so we can not say electron is only energy
    In physics energy has define and it's capacity to do work
    Energy hasn't spin or charge and can not travel through spacetime .
    A wave can travel through spacetime .
    Photon carry energy and after absorption phenomena electron carry energy of photon after destroyed photon .

    We know energy can not create or destroyed but photon can destroyed and create
    Before destroyed photon , photon transfer all energy and momentum to electron in absorption phenomena .
    So it's not easy say they are same things .
    electron and photon are wave-particle and have wave function in quantum field theory .
    can we consider energy a wave and have wave function ?

    Thank you for your good explanation .
  9. Nov 28, 2012 #8

    Simon Bridge

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    Nobody does - we say that "mass" and "energy" are the same thing.
    The mass-energy equivalence is something Einstein did demonstrate and it is fundamental to modern physics.
    (Though: in Grand Unified Theories, the apple and the electron and energy are all thought to be aspects of the same super-object.)
    ... rest-energy is available to do work too.
    energy can and does travel through space in a number of forms - the concept of "travel" is tricky to apply to "space-time".
    A photon can pair-produce to make an electron and a positron ... the total kinetic energy of the e-/e+ pair is less than the photon's energy: where did it go?

    When a neutron joins a hydrogen atom to make deuterium, the mass of the duterium is less than the sum of the hydrogen and the neutron masses. Where did it go?

    We have been converting energy to mass and back again for decades (deliberately since 1939 - re. Cockroft & Walton). So it is pretty easy actually. It is harder to accept though, since it flies in the face of daily experience.

    If you are referring to wave-particle duality - they are all particles. This is why the field is called "particle physics". There is a wave-formulation of the theory though. What we detect, though, is particles.
    It is possible to have a wave of energy - just like you can have a wave of position or pressure or probability.
    A wave-function is a wave of probability (amplitude). You will never find a probability amplitude in nature though they are very useful for predicting the distributions of particles - which you can detect - as well as many properties such as position, momentum, and kinetic energy. The wave-function for an electron is, however, not the same as an "electron wave".

    The energy-eigenvalue of a particle in a box (say) is it's kinetic energy. It also has energy stored as spin, and in it's EM field, and as mass which may be released in, for example, nuclear reactions.

    ... mass-energy equivalence: experimental verification

    ... Feynman on wave-particle duality (in QED) ... to give you an idea how I can say that they are all particles even though there are wave formulations of the theory.
    Last edited: Nov 28, 2012
  10. Dec 3, 2012 #9
    what's that number of forms ?
    anything expect ( photon , quark , electron , positron , leptons , and other particles ) that we know in standard model ?

    But these forms are not energy
    They are wave and have some properties that energy hasn't them ( properties ) .

    The energy exchange to rest energy !
    But what happening in pair production ?
    photon is 1 wave and after decays we have 2 waves
    A photon decays to 2 waves ( an electron and a positron ) because a wave can carry energy and momentum .

    wave is not energy
    it create in pair production to carry momentum and energy of photon after decays .

    in Compton scattering a photon can transfer some of energy to 1 electron and after that we can consider that electron get more kinetic energy and jump to higher energy level and then electron return to lower level energy and emit a photon .
    So what happen in this phenomena ?
    Another wave ( photon ) create .
    In beginning of this process we have a wave ( photon ) but in the end we have 2 waves .

    Can we say photon and energy are same thing ?
    If yes we have two term in physics .

    1 - energy can not create or destroyed .
    2 - photon can create and destroyed .

    if we replace energy to photon in secondary sentence , we have :
    1 - energy can not create or destroyed .
    2 - energy can create and destroyed .

    How you can explain this paradox ?

    Sorry for delay i'm too busy .
  11. Dec 3, 2012 #10

    Simon Bridge

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    Energy has different forms - like kinetic and potential energy.
    You will notice that kinetic energy is not always conserved: it is possible to create and destroy kinetic energy.

    A Photon is also a form of energy - there is no problem with forms of energy being created and destroyed.
    The form may change - but the energy remains.

    Please understand, when two quantities are related only by a constant multiple, we say they are different ways of looking at the same thing.
    So kilograms and pounds are different ways to look at mass... you can tell because they are related by a constant multiple (1kg=2.20462lbs).
    Energy and frequency of a photon are the same thing (related by plank's constant).
    Mass and energy are the same thing thing too, for the same reason (related by the invariant speed of light).

    The wikipedia entry you linked to points out that, in the standard model, energy and mass are understood in terms of interactions between fundamental particles.
    The standard model is a particle model. So, you description of pair production (above) really needed to be in terms of particles, not waves. It is not even clear what you mean by "waves" in your description.

    Please see the links I provided last post so you will be able to understand what is being said to you better.
    Last edited: Dec 3, 2012
  12. Dec 6, 2012 #11
    Last edited: Dec 6, 2012
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