Time Theories: Outta Universe, Relativity, Multiverse

[khotsofalang]

how does one define time? iv we viewed time from outta our universe...would einsteins theories of relativity still hold...i mean would any of the laws of physics in our universe hold if we assumed the multiverse model of the universe(s)?

 

[Chalnoth]

how does one define time? iv we viewed time from outta our universe...would einsteins theories of relativity still hold...i mean would any of the laws of physics in our universe hold if we assumed the multiverse model of the universe(s)?

The physical laws of our universe are internal to our universe, and they'll hold (at least to within current experimental accuracy) for any observer.

As for what time is, well, that depends somewhat upon what physical theory of the universe you're using. In relativity, for instance, time is just another direction things move, like the three directions of space. In quantum mechanics, time is a parameter over which things change.

 

[khotsofalang]

can't we define time as another form of energy? well i mean it obeys the laws of conservation quite well. in fact if time was created during the big bang then it must have been made from some form of energy... the problem is whether we can convert energy into time... or vice versa, if its not possible then what are the constraints?

 

[Chalnoth]

can't we define time as another form of energy? well i mean it obeys the laws of conservation quite well. in fact if time was created during the big bang then it must have been made from some form of energy... the problem is whether we can convert energy into time... or vice versa, if its not possible then what are the constraints?

No. Time and energy are quite distinct. Time is absolutely not a conserved quantity. It doesn't even make sense as a conserved quantity, any more than position could be considered a conserved quantity.

Think about it this way: energy is a property of a specific object. It will have some amount of energy related to its internal degrees of freedom (we call this mass) and some amount of energy related to its motion (we call this kinetic energy). But in any event, energy is a property of that object itself.

Time, on the other hand, is a coordinate. It is not a property of the object, but it is instead a statement of where the object is. We say that an object is at a certain place at a certain time, for example. But this isn't a property inherent to the object or its behavior. It is just a statement of its location.

 

[narrator]

If the progress of time is just one of four vectors, does it follow Newton's third law of motion?

 

[Chalnoth]

If the progress of time is just one of four vectors, does it follow Newton's third law of motion?

Huh? Newton's third law is about opposing forces: when one object applies a force on another, there is necessarily an equal force (pointing in the opposite direction) of the other object back on the first. So if I push on a wall, the wall pushes back on me with equal force.

I don't see how this concept makes any sense whatsoever in relation to time.

Also, a small nitpick: time isn't "one of four vectors". Rather, it is a component of a four-dimensional vector. The four numbers (three space, one time) together make up a single vector. You can compose similar four-vectors for other quantities. There is an energy-momentum four-vector, for instance (three components for momentum, one for energy). You can similarly compose a four-force with three components that are proportional to acceleration (good old F=ma), and one that is proportional to the change in energy over time.

 

[Tanelorn]

This "what is time" thread seems like a parallel universe to my "what is space" thread :)

So what are the properties of time?

 

[narrator]

Huh? Newton's third law is about opposing forces: when one object applies a force on another, there is necessarily an equal force (pointing in the opposite direction) of the other object back on the first. So if I push on a wall, the wall pushes back on me with equal force.

I don't see how this concept makes any sense whatsoever in relation to time.

Yes, or per the cliche quote, for every action there's an equal and opposite reaction.

I guess the question is, was/is time an action? Did/does it propel forward, and thus something else propels backwards? When time was first set in motion, did something go (crudely put) in the opposite direction? And when something distorts spacetime, does it also cause an equal and opposite spacetime reaction?

Also, a small nitpick: time isn't "one of four vectors". Rather, it is a component of a four-dimensional vector. The four numbers (three space, one time) together make up a single vector.

Oops, you're right, my bad. Feel free to nitpick.. ;)

 

[Chalnoth]

Yes, or per the cliche quote, for every action there's an equal and opposite reaction.

I guess the question is, was/is time an action? Did/does it propel forward, and thus something else propels backwards? When time was first set in motion, did something go (crudely put) in the opposite direction? And when something distorts spacetime, does it also cause an equal and opposite spacetime reaction?

I think you're confusing terms here. Newton's third law applies to forces and only to forces. It only applies to the sorts of things you would place on the left hand side of the equation F=ma. The use of another word for the same thing (action) doesn't change this at all. It's still a statement about the relationship between forces.

A perhaps related question that expresses yours (hopefully) more accurately would be to ask whether or not there exists some higher-order law that would result in similar behavior with respect to time (e.g. when you create a universe that has a future forward in time, you also create a reflection with its future going backwards in time). Well, as far as I know, that is just not known at this time, and there isn't any good reason to believe it might be the case either.

 

[narrator]

I think you're confusing terms here. Newton's third law applies to forces and only to forces. It only applies to the sorts of things you would place on the left hand side of the equation F=ma. The use of another word for the same thing (action) doesn't change this at all. It's still a statement about the relationship between forces.

A perhaps related question that expresses yours (hopefully) more accurately would be to ask whether or not there exists some higher-order law that would result in similar behavior with respect to time (e.g. when you create a universe that has a future forward in time, you also create a reflection with its future going backwards in time). Well, as far as I know, that is just not known at this time, and there isn't any good reason to believe it might be the case either.

Thanks Chalnoth.. your second para is just what I was getting at..

And re the first para, I guess in terms of F=ma I considered time to be notionally connected to the 'acceleration' part.

 

[Chalnoth]

Thanks Chalnoth.. your second para is just what I was getting at..

And re the first para, I guess in terms of F=ma I considered time to be notionally connected to the 'acceleration' part.

Well, sort of, I guess? Acceleration is the rate of change of velocity over time. So time is involved, but there is no way to simply equate them.

 

[Ashwin_Kumar]

i'm not too sure about einstein's theories holding, because i don't believe in the curvature of spacetime being solely the cause of gravitation, but time definitely exists. A multiverse must exist, and time has to run in that. Our universe expands into this time and space in this multiverse.

 

[Chalnoth]

i'm not too sure about einstein's theories holding, because i don't believe in the curvature of spacetime being solely the cause of gravitation, but time definitely exists. A multiverse must exist, and time has to run in that. Our universe expands into this time and space in this multiverse.

Well, there really is no doubt that General Relativity breaks down at some point. It has to, because it makes some nonsensical predictions (singularities).

However, there isn't really any question that space-time curvature is the sole cause of gravitation. The real questions are what that curvature actually means (especially on very small scales), and whether the relationship between curvature and the behavior of matter is as we currently believe it is (this could lead to a modification of gravity on any scale, in principle). For example, gravity has a number of thermal behaviors, where even perfectly empty space-times can have temperature. But usually, something having a temperature is a result of the collective behavior of very small particles. This is, in fact, where our current understanding of thermodynamics comes from: the laws of thermodynamics can be derived by simply assuming that matter is made of atoms and molecules which individually obey Newton's laws. So the question is: what are the little bits of curvature that make up what we see as gravity?

But to propose a deviation of gravity entirely from curvature, well, you're fighting against quite a large body of experimental evidence.

 

[petm1]

I guess in terms of F=ma I considered time to be notionally connected to the 'acceleration' part.

Each part and the whole of F=ma are temporal notions of motion relative to past measurements.

 

[dimension10]

how does one define time? iv we viewed time from outta our universe...would einsteins theories of relativity still hold...i mean would any of the laws of physics in our universe hold if we assumed the multiverse model of the universe(s)?

No, but a theory of everything would.