Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Characteristics of light when traveling long distances in space ("fabric" of spacetime?)

  1. May 9, 2017 #1
    how do we know light stays consistent when traveling through the "not nothingness of space"? how do we know the rate at which light degrades as it travels through the medium that has to be there?
     
  2. jcsd
  3. May 9, 2017 #2
    I want to help but I didnt understand your question
     
  4. May 9, 2017 #3
    Ok, isn't there a substance within "empty space" that was at least once called aether?
     
  5. May 9, 2017 #4
    Theres no substance in empty space.Theres no aether.

    In old days people thought that "waves" need medium to travel.Like sound need a medium etc.So people in those days thought light is a wave so it should need a medium to travel which they called it aether.But Michelson–Morley experiment showed us that, theres no aether.
     
  6. May 9, 2017 #5
    ah, but there was two conclusions derived from that experiment, or so I've read. I also read that Einstein said there has to be something or gravity its self didn't work. my understanding of that experiment was more or less deemed "inconclusive". if there is no medium, how does gravity work? I veiw gravity as pushing, not pulling. is that false?
     
  7. May 9, 2017 #6
    :welcome:
    Is your question about light or gravity? It seems like you are mixing concepts together where you don't have to...
    Indeed, scientists once believed there was a medium (which they called the aether) in which light needed in order to travel. This was disproved, as electromagnetic waves do not need a medium to travel through.
    If you have questions about gravity, could you elaborate on them a little bit further?
     
  8. May 9, 2017 #7
    Where ? Any source ?
    Its not inconclusive..Its a fact of nature..Light doesnt need a medium to travel.
    "Spacetime tells matter how to move; matter tells spacetime how to curve"(John Archibald Wheeler)
    .Gravity is a fact of space-time curvature.
    Pushing pulling is strange words to describe the situation I guess.I would say matters attract each other
     
  9. May 9, 2017 #8
    my question is how do they know how far light can travel? I think the term "space-time" needs further evaluation because I don't understand how gravity works if there's just nothing in space to bend. and if there is something, how do we know it's true effect on light?
     
  10. May 9, 2017 #9

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    The fact that you don't understand something doesn't make it wrong.
     
  11. May 9, 2017 #10
    do you understand what makes gravity? think of a surffer, does the wave push or does it pull him? so, what is it that mass bends to make gravity happen? I'm under the impression that science still doesn't understand gravity or what really causes this effect. how can something bend nothing?
     
  12. May 9, 2017 #11

    russ_watters

    User Avatar

    Staff: Mentor

    What is "known" so far is what has been observed: light has no problem traversing the entire width of the visible universe. So there is good reason to believe it travels forever.
    By observing how light behaves.
     
  13. May 9, 2017 #12

    russ_watters

    User Avatar

    Staff: Mentor

    The idea that space can be empty and yet have a geometry (and other properties) may be difficult to wrap your mind around, but it is well supported by observations.
     
  14. May 9, 2017 #13
    Because GR predicted that predicted very massive objects would act as a gravitational lens,
    Then some time later, as telescopes improved, that is exactly what was observed.
    https://en.wikipedia.org/wiki/Gravitational_lens
     
  15. May 9, 2017 #14
    Per Wikipedia (Outer Space) referencing Davies, P. C. W. (1977), p. 93, The physics of time asymmetry

    "...the mean free path of a photon in intergalactic space is about 10E23 km, or 10 billion light years."

    It should be noted that at the Earth's surface a photon's mean free path (MFP) through air at standard temp and pressure is only about 2 meters, and the MFP is so short due to the vitreous humor in the eye that the photons that are absorbed by the retina are actually emitted within the eye itself (so even when star gazing these are brand new fresh photons, not "old ones" from outer space).
     
  16. May 9, 2017 #15
    ok, I guess what I should ask is what causes the force of gravity? mass has to interact with something to cause gravity. Einstein coined the phrase space-time, what is space-time? what makes up the fabric of space? and how on earth can we say this "fabric" doesn't have more of an effect on light then we think? I don't care what the Michelson-Morley experiment says because to me it just says light is really fast.
     
  17. May 9, 2017 #16

    russ_watters

    User Avatar

    Staff: Mentor

    The general answer to the question of "what is....?" anything, is that the thing you want to know about "is" the sum of its known and theorized properties. This is likely to be unsatisfying to you because the known/theorized properties of space are probably less than you want to believe it has.
    By observing how light behaves in it.
    That isn't a very good approach to learning.
     
  18. May 9, 2017 #17
    you're right, it might not be the right approach. I'm saying the scale of that experiment is nowhere near big enough is why I say that. I just never put much thought into what is space-time until I asked myself who to say there isn't something reacting on the photons to slow them down or absorb or destroy them. I'm questioning how do we really know what the effect that this "fabric" has on light? the only way we could tell is to send a probe deep into space, shoot a laser at it and see what happens. then go further and see what happens. just because we made these tests and experiments on earth and not truly in space. or am I missing something? i just had a thought that if this fabric does effect light more than we think it does, then the math is wrong.
     
  19. May 9, 2017 #18
    guess the real answer is I should have went to a school that I could never afford. thanks for trying to help me understand.
     
  20. May 9, 2017 #19

    russ_watters

    User Avatar

    Staff: Mentor

    I'm not sure what you mean, but ok...
    Yes; astronomy. We learn a lot about space by observing light that has traveled across the universe.
    Clearly. But the math describes very well what is observed.
    You're welcome, but don't give up on learning just because you didn't go to school for it. It's true that you won't be able to learn it to the same depth as a college degree, but there is some good learning you can do.
     
  21. May 9, 2017 #20
    what if the math was forced just to fit a model? no I'm not a flat earther, but they have math that works too, or so it seems. what if our math is wrong too? I asked this question and all of a sudden everything moved in closer and got smaller. we are told what numbers we have to use, and it seems to me that there's a chance it could be wrong. would the math still work if everything is closer, I think it would. 2+2=4...unless one of the 2s is actually a 3. again, thanks.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Characteristics of light when traveling long distances in space ("fabric" of spacetime?)
Loading...