Is Time Influenced by Mass and Matter?

[Timmaay322]

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...

 

[FunkyDwarf]

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.

 

[Timmaay322]

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...

 

[DaveC426913]

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...

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.

 

[Timmaay322]

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...?

 

[DaveC426913]

SO,
Are you saying that time does not exist in a vaccume? 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...?

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.

 

[Naty1]

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...

 

[Timmaay322]

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)

 

[jefswat]

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)

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

 

[DaveC426913]

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.

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

If a photon didn't have mass why wouldn't it just go c in a straight line forever.

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.

 

[Timmaay322]

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 let's 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.

 

[Timmaay322]

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.

 

[Naty1]

Timmaaay...mass is not the only entity affected by gravity...so is energy, pressure and of all odd things, time!

 

[Timmaay322]

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?

 

[DaveC426913]

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?

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 traveling 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.

 

[Timmaay322]

two photons traveling parallel and passing near Earth, will follow "straight" paths, yet they will no longer be parallel; they will converge.

This makes no sense to me.

 

[DaveC426913]

This makes no sense to me.

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" is common. I used it in the Earth and beachball example. And space-time is most definitely non-Euclidian.

 

[jefswat]

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.

 

[cragar]

I kind of have a question of my own let's 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.

 

[DaveC426913]

I kind of have a question of my own let's 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.

Pretty much, yeah.

 

[Timmaay322]

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?

 

[DaveC426913]

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?

Right.

So than if mass didn't exist space-time would not be curved. Right?

Not quite. Energy causes curvature as well.

All that aside though, how space-time gets curved doesn't really factor into why photons follow the curve.

 

[Timmaay322]

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)

 

[Timmaay322]

Dave please enlighten me with your knowledge...

 

[cragar]

this might be a dumb question but does time exist without space. or are space and time one thing.

 

[DaveC426913]

this might be a dumb question but does time exist without space. or are space and time one thing.

Space-time. One thing, four dimensions.

 

[Naty1]

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.

I don't necessarily buy the answer above...all might emerge at the same simultaneous instant...but time is necessary for change.. for the development of some type of energy singularity (if that's what started everything)...

But, as our argument continued, and eventually ended with the fact that as mass and energy curve space-time, a photon does not

NOT SO!

A photon has energy...energy curves spacetime...therefore a photon DOES curve spacetime...although infinitesimally of course...another way to think about is that mass and energy are equiavlent via E = mc²...so if mass curves spac etime...so does it's other form...energy...

Even the sound of your voice will curve (alter) spacetime...why?? because it carries energy different from ambient and that energy will curve spacetime...of course it can be ignored in most cases because its so tiny...

"I haven't had any time to really think about this, but will be haunted by it later." Good for you...anybody who starts out and thinks they REALLY understand this hasn't thought about it much!...Einstein started at age 16 wondering what light would look like when he caught up to it...

 

[Timmaay322]

Ok so I still haven't been convinced a photon doesn't have mass. If it has energy it would have to have mass right? I haven't looked into the deep understanding of energy, I just know that kinetic, potential, and e = mc^2. This also brings me to not understanding how objects that don't have mass follow the path of space-time. Matter takes up space... So if an "object" had no mass, it wouldn't take up space. So itwouldn't follow the path of space. Right? Thoughts...

 

[millitiz]

hi Timmaay,
actually, E = mc^2 was a bit misleading, and might cause your confusion.
In fact, the whole equation is
E^2 = (pc)^2 + (mc^2)^2.
As you can see, it also included an extra term of momentum. Now, do not think Momentum in the classical sense, that is, p no longer equals to mv.
So indeed, it is possible for photon to not have "rest mass", it just simply means that all of its energy is contributed to momentum (or in another way, kinetic energy).
From this perspective, one could kinda see that nothing could move faster than the speed of light because some of the energy contributes to rest mass energy
Of course, this is such an interesting topic that one could go on and on and on, and deeper and deeper (wouldn't take too long for me to be out of my depth though :P). But I would like to stop at here, and turn into another way of explaining it (well, it is more of my hypothesis at this state).

Another way of thinking of it (although this I really needed to verify with my professors: that is to say, I am not 100% sure about this) was this: So for Gravitational field, Electro, magnetic field, instead of thinking of field line, one could think of mediators. i.e., for electro force/ field, the mediator is photon (and that lead to some theories of "graviton"). These photons carry some info between electrons, and photons were exchanged between electrons (to get a more comprehensive understanding, this is called QED, quantum electrodynamic. And "Particle Physics" by David Griffens had some good intro analogy of it in the, I believe the first 2 chapters).
Now, here is the place I kinda need to have verification. So if the mediators are massless, then the force/field would be inverse proportional to r^2. However, if the mediator carry even just a bit mass, then by the the law of motion, it would no longer follow the inverse square law (There are some researches conducted on this and trying to test the Gravitational field, and the possibility of the existence of graviton).
Electro field, if you recall, is proportional to the coulomb force, which was inverse proportional to r^2. (Here is the part I am not fully convinced, because there was no way that it must be.) And by QED, the mediator is photon. So to let the field be inverse proportional to r^2, photon MUST have no mass.
I hope this explains a bit if not confuses you even more. If it didn't, then simply just throw it out of the window.

 

[millitiz]

btw/
effective mass is also a bit misleading. For simplification and your health, my own suggestion is to throw it out of the window, too. :)
Because the effective mass, by its own definition, somehow includes momentum and rest mass.
So really, the orthodox way of thinking it is still: E^2 = p^2 + m^2, c = 1.
Oh, end it normally take awhile to actually accept some of the new concepts (at least that is how it worked for me. For instance, at first, c is constant was very frustrating for me. And even now, which I considered that I am more sophisticated in physics, there are still something that frustrates me when I take the first glance. So I believe your frustration was pretty normal, and I believe that you can overcome it by repeatedly thinking about it.
Good luck!

 

[DaveC426913]

Matter takes up space... So if an "object" had no mass, it wouldn't take up space. So itwouldn't follow the path of space. Right? Thoughts...

On what basis do you build your logic? Common sense? Analogy to classical mechanics?
None of these apply.

A photon behaves how a photon behaves.

A Bornean bushman would try to understand how a Blackberry works based on his understanding of yodeling and smoke signals. And we would tell him "there's no counterpart in the world you're familiar with. It is what it is. We'll happily show you the math, but don't bother trying to relate it to anything you're used to."


I'll try to explian it once again: You seem to be thinking that, somehow, even though space is curved, the photon should ignore this curve and ... what? go straight? As if the curve of space is somehow mapped onto a "higher", more "real" space where things are "actually" straight? There is no "higher space" where the photons would somehow know what "true straightness" is.

No, the photon follows a straight path. Because that's what photons do. They go straight. They always go straight.

The issue here is that "straight" is defined by the force of gravity.

 

[Mzachman]

Here is my thought. And it's just a thought from someone who probably knows nothing. So tell me if I'm wrong if I am. haha

Ok, your "effective mass" comes from E=mc^2, correct? We know that the photon has no rest mass. So by having no rest mass, but having "effective mass", that means it has some sort of energy through E=mc^2.

In this case it is the energy that we know the photon carries. So if you could somehow "stop" the photon without releasing that energy, it would have mass... rest mass. Only problem is that the photon IS energy itself, and travels at one speed ONLY. Meaning, if you stop it, all energy is removed (put into something as heat, etc.). By all energy being removed, it means it literally doesn't exist anymore. This proves that it has no true mass. It may have an "effective mass" and momentum through E-mc^2 and p=h/lambda, but if you try to "stop" the photon, all of the energy it contains leaves, and leaves no energy or mass whatsoever...

That didn't come out nearly as clearly as it was in my head. I'm kinda new at getting those things out... but maybe it will start an idea and someone more experienced in this can speak up. I hope it helps a little bit.

 

[stone1]

When a nuclear (uranium, for example) bomb explodes, lot's of light (photons) comes out. Where were these photons before the explosion? Binding the atom. Was the mass of the atom affected by the binding energy? You bet. So where is the issue?

 

[protonchain]

hi Timmaay,
actually, E = mc^2 was a bit misleading, and might cause your confusion.
In fact, the whole equation is
E^2 = (pc)^2 + (mc^2)^2.
As you can see, it also included an extra term of momentum. Now, do not think Momentum in the classical sense, that is, p no longer equals to mv.
So indeed, it is possible for photon to not have "rest mass", it just simply means that all of its energy is contributed to momentum (or in another way, kinetic energy).

QFT

The energy of a photon is basically E = \frac{hc}{\lambda}

h is a constant, c is a constant, \lambda is the wavelength. No mass needed.

Now let's wait for timmay to go "I still am not convinced that photons don't have mass."

 

[cragar]

E=hf

 

[benk99nenm312]

Well first of all that doesn't convince me that a photon is massless...

Photons have relativistic mass. Does that satisfy you?

A photon is massless. Sorry.

 

[Naty1]

Timmaay:
I don't think it's particularly important for you to believe that photons have no mass, maybe it's better you don't believe it, but it is important to accept that current science says that's the case. The current explanation is that photons do have energy and since mass and energy have some deep connection, both energy and mass happen to curve spacetime. Nobody knows why yet.

Einstein did not believe that space and time were fixed and immutable when everybody else did;instead he thought the speed of light was fixed and immutable. He understood the conventional explanation at that time produced anomolies which he did not believe. So he created a new theory, one that was logical and could be verified experimentally. He turned out to be right!

Since nobody even knows what mass and energy really are at a fundamental level, maybe its useless to argue about these two different forms of what is likely a unified (single) entity. All we know today is that they appear different to us and E = mc² explains the observed relationship.

 

[Dale]

By the way, there is no way to experimentally confirm that a particle has 0 mass. All you can do is put an upper bound on the mass. Specifically, if an experiment determines the mass to be zero to within experimental error then the experimental error itself becomes an upper bound on the mass. Currently, the best upper bound on the http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html" is 7E-17 eV/c² (1.2E-52 kg). So the assumption of 0 mass is pretty reasonable IMO.

 

[protonchain]

By the way, there is no way to experimentally confirm that a particle has 0 mass. All you can do is put an upper bound on the mass. Specifically, if an experiment determines the mass to be zero to within experimental error then the experimental error itself becomes an upper bound on the mass. Currently, the best upper bound on the http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html" is 7E-17 eV/c² (1.2E-52 kg). So the assumption of 0 mass is pretty reasonable IMO.

I guess apart from measuring the mass/estimating it, we can usually assume that something has to have 0 mass in order for it to reach c right?

 

[Dale]

Right, but the same statement applies. We cannot experimentally confirm that a particle travels at exactly c, all we can do is determine the speed to be c to within experimental error.