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Does time exist without mass?

  1. Mar 25, 2009 #1
    If time is a measurement of an event/period, does the event/period require the change in shape/distance of a mass? What else could you measure in order to determine a time?
    Anyone have any answers for me? When I googled these thoughts I couldn't really find anythign so that lands me here...
     
  2. jcsd
  3. Mar 25, 2009 #2
    You don't require mass because you could, for instance, measure the distance covered by a photon in a certain period of time/time it takes for photon to traverse said distance. Basically you just need some quantity that changes with time and be able to measure it.
     
  4. Mar 25, 2009 #3
    Well, I didn't want to bring the debate of whether a photon has mass or not. Because it hasn't been proven proven either way... or has it and i'm just ignorant. The basis of my question was more on the idea that (besides measuring a photons path) time is a measurement on a masses effect of space. i.e. pendulum swinging back in forth, growth of a plant, etc... So I am looking for more understanding on that...
     
  5. Mar 25, 2009 #4

    DaveC426913

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    Whether or not a photon has mass, it does have a frequency and a wavelength, both of which require time to measure, even in the absence of any mass.
     
  6. Mar 25, 2009 #5
    SO,
    Are you saying that time does not exist in a vaccume?

    and

    Are you willing to say that at absolute zero when all matter stops, will time stop? or does light not depend on temperature and if a photon enters space of absolute 0 it will act no differently so time does not stop...?
     
  7. Mar 26, 2009 #6

    DaveC426913

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    I'm not saying any of these things. You seem to think that I'm saying "time does not eixst without photons". No, I'm simply saying time doesn't stop simply with the absence of matter, as witnessed by the fact that photons make their way through empty space quite nicely.

    I have no reason to think time stops under any circumstance. The onus is on you to demonstrate why it might.


    BTW, all matter does not stop at absolute zero. Look up Bose-Einstein condensate.
     
  8. Mar 26, 2009 #7
    No one knows the answer to your question for sure....at Planck scale (very,very tiny, perhaps the limit in discreteness) it appears that quanum jitters disrupt everything as we know it...there is no space,time,mass,etc as we perceive it....just energy fluctuations.....so when a universe is born, are there any universes without mass?? Possibly, but noboldy really knows....maybe one emerges and instantaneously self destructs....maybe there are billions upon billions of them.....

    what emerges from a quantum fluctuation and a subsequent big bang appears to be mass,energy,time,etc but whether all MUST emerge together is not at all certain since general relativity and quantum mechanics don't work well at such singularities.

    If you subscribe to the theory of multiple universes, then if there are an infinite number of universes it becomes more likely just about every type imaginable might originate...but which survive to generate additional universes is yet another unknown question.

    It would seem to me, a layman, time without mass is more likely than mass without time, but we have been constantly surprised by what we find....
     
  9. Mar 26, 2009 #8
    Well I still don't understand why a photon doesn't have mass... The fact that it is effected by gravity convinces me that it does. When people say that a photon just follows the path of space time, doesn't it need mass to do that. If a photon didn't have mass why wouldn't it just go c in a straight line forever. BUt since mass has the ability to stop, deflect, etc a photon why wouldn't the photon have mass? I know this is getting a little off topic and unless there is another thread answering my exact questions here I would like someone to answer this here. (I did start this thread so it's ok with me)
     
  10. Mar 26, 2009 #9
    Space-time is warped by lots of things so space really isn't flat. The reason light can't go in a straight line is the same that you can't draw a straight line on the surface of a sphere. It necessarily has to be curved
     
  11. Mar 26, 2009 #10

    DaveC426913

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    Why would a photon need mass merely to go in a straight line?
    It does.

    It does go in a straight line. A straight line in curved space-time is curved!


    Take two dinky toys and place them parallel to each other on a beachball. Drive each dinky toy straight. They will eventually meet. It is not because the dinky toys are being curved by the beach ball; it is because the straight line that the dinky toys are following is curved. This is non-Euclidean geometry.
     
  12. Mar 26, 2009 #11
    Your analogy makes sense, but I don't think it satisfies me. The reason the toys have a curved path is because there is a force making them follow a curved path. Right? If there was no gravity or force attraction between the toys and the ball the toys would go off in a tangent forever. AND, didn't Einstein prove that with his idea of gravity and shooting a cannon-ball from the earth. If it wasn't for gravity (or any other forces) the ball would go straight forever. Right?
    So lets say:
    c = no mass
    c = constant velocity, i.e. goes in straight line forever, therefore not being effected by gravity.
    But it is effected by gravity.

    Maybe that analogy you gave me was not relevant to what I am asking... or maybe I'm unaware of something that answers my questions... but I still haven't been convinced that photons are massless.
     
  13. Mar 26, 2009 #12
    I just thought of something as I was eagerly awaiting your reply Dave.

    Back to the cannon ball theory, or anyone like it. If I through a ball at a wall 2 meters away from me, the ball will bounce back because the force of the wall pushed the ball away. A photon, which has no mass according to Dave and many other people, should go straight through the wall. Because the wall will not create an equal and opposite force against the massless photon. And that is my analogy of a photon going straight forever in space-time. I haven't been convinced that if a photon has no mass, then space would not effect it. But space does effect it in our universe.
     
  14. Mar 26, 2009 #13
    Timmaaay...mass is not the only entity affected by gravity.....so is energy, pressure and of all odd things, time!!!!!
     
  15. Mar 26, 2009 #14
    Well first of all that doesn't convince me that a photon is massless....

    But pressure and energy are directly related to mass.
    Pressure being a force and e=mc^2
    So how does that lead to a photon not having mass?
     
  16. Mar 26, 2009 #15

    DaveC426913

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    No no. The "curved path" I'm speaking of is not "around the ball", the curved path is "towards each other". Parallel lines on a curved surface will converge.

    At Earth's equator, the meridians of longitude are parallel, yet they converge at the poles. If you parked two cars on the equator, making sure they were both perfectly parallel, and then you drove each of these two cars in a straight line from the equator to the poles, the cars would crash into each other at the pole - even though they started off parallel and have have both driven along perfectly straight lines.

    In the same way, two photons travelling parallel and passing near Earth, will follow "straight" paths, yet they will no longer be parallel; they will converge. Not because of any force, but because the very geometry of what it means to be a straight line is now not the same as it was out in flat space. This was Einstein's gift to us.
     
  17. Mar 26, 2009 #16
    This makes no sense to me.
     
  18. Mar 26, 2009 #17

    DaveC426913

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    That is because you have only ever studied Euclidean Geometry, where, for example, parallel lines never converge. http://en.wikipedia.org/wiki/Non-Euclidean_geometry" [Broken] is common. I used it in the Earth and beachball example. And space-time is most definitely non-Euclidian.
     
    Last edited by a moderator: May 4, 2017
  19. Mar 27, 2009 #18
    You have to imagine yourself on the surface of the sphere where (to you) it is only 2 space like a plane. Don't let yourself get confused by involving anything other than the surface. Things necessarily get harder to see when you get to 3 space but the same conclusions still apply.
     
  20. Mar 27, 2009 #19
    I kind of have a question of my own lets say at the start of the big bang if there was a start , wouldn't time have to be the first thing to exist to allow things to have an existence in the physical sense to allow things to be timed.
     
  21. Mar 27, 2009 #20

    DaveC426913

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    Pretty much, yeah.
     
  22. Mar 27, 2009 #21
    I understand what you are saying, and I can understand non-Euclidian. But, I what I am trying to understand is that doesn't some force cause space-time to be non-Euclidian. I assume the reason space-time is curved is because mass causes it to be. Right? So than if mass didn't exist space-time would not be curved. Right?
     
  23. Mar 27, 2009 #22

    DaveC426913

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    Right.
    Not quite. Energy causes curvature as well.

    All that aside though, how space-time gets curved doesn't really factor in to why photons follow the curve.
     
  24. Mar 27, 2009 #23
    Alright. At school today I was in a computer lab studying and noticed a class (physics 3, I am currently in 2) was ironically watching a video on SR. So, I took a break and started watching from the hallway. Eventually the professor came out and he and I sparked a conversation about exactly this, because I asked him these same questions.

    One thing that helped me understand and not understand at the same time was that a photon has a rest mass of 0 (already knew that) but also has an effective mass. Of course I knew that e = mc^2 was, but I never thought of relating a photon to an effective mass. At this point I thought I was sure that a photon does have mass. But, as our argument continued, and eventually ended with the fact that as mass and energy curve space-time, a photon does not. Implying that a photon does not have mass. So, at the end of the conversation (10 minutes ago) I am more confused than before. I would have asked more questions, but he was in the middle of a class, so did not.

    Lets analyse the properties of a photon:

    Has 0 rest mass. This explains why only a photon can reach c.
    Has effective mass. This explains it is energy?, but has no mass...?
    Has momentum. This explains that it has mass....?
    Follows the path of space time. This explains nothing about mass.

    I haven't had any time to really think about this, but will be haunted by it later. During the conversation he stated that an object does not have to have mass to follow the path of space time. This still confuses me. Mainly on the idea that I can;t think of any object with no mass. Can anyone give me an example or a good analogy of another cirumstance for this statement.
    (Don't say a photon! And don't say energy because that is the same as saying mass)
     
  25. Mar 29, 2009 #24
    Dave please enlighten me with your knowledge...
     
  26. Mar 29, 2009 #25
    this might be a dumb question but does time exist without space. or are space and time one thing.
     
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