# Time and space

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I think time and space are intertwined and cannot be separated. To confirm/verify, let me pose the following questions:

1. Is there some experimental data that proves that time is actually another dimension? Or maybe theoretical explanation?

2. Had anyone explained in detail what time is and why it is what it is? Or we just rely on some intuitive understanding of "time"?

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They are intertwined which is typically the nature of spacetime and what relativity represents. The observed rate at which time passes depends on an object's velocity in relation to an observer as well as the intensity of strength of the gravitational field causing time to pass slower. Because of this, time cannot be separated by the three dimensions of space.

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The observed rate at which time passes depends on [...] the intensity of strength of the gravitational field[...]. Because of this, time cannot be separated by the three dimensions of space.

Nitpick questions like "what is the 'intensity of strength'? " aside: your point is that time and space cannot be separated (whatever that may mean) because the passing of time depends on the location?

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1. Is there some experimental data that proves that time is actually another dimension? Or maybe theoretical explanation?

Any experiment that is consistent with special or general relativity provides evidence that thinking of space and time together is correct. We have many indirect tests of this also, for example the success of the standard model.

Mathematically, space-time is a manifold and in general there is no canonical way of deciding coordinate should be time and what ones should be space.

Importantly this is true on Minkowski space-time. There is a preferred class of coordinates, the inertial ones but even these will "mix space and time" between them.

It is this that is at the root of all the "paradoxes" of special relativity.

2. Had anyone explained in detail what time is and why it is what it is? Or we just rely on some intuitive understanding of "time"?

We know how to model time, we know how to use it in classical and quantum mechanics. We know how to describe time in special and general relativity. However, I don't think you will find a real convincing explanation of what time is. To a large extent I think we should not spend too much time on this question as understanding how to model and use time is more important.

Our understanding of time may well be modified when a proper understanding of quantum gravity is achieved.

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Nitpick questions like "what is the 'intensity of strength'? " aside: your point is that time and space cannot be separated (whatever that may mean) because the passing of time depends on the location?

Time dilation is a result of an area's particular gravitational strength and dependent on an object's velocity and the rate of which time passes in accordance to general relativity, which is why you would age quicker when stationed on the ground and age much slower when higher in the atmosphere or flying at high speeds. It is the constancy of the speed of light that would keep them intertwined.

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Time dilation is a result of an area's particular gravitational strength...

You also have time dilation in special relativity where the gravitational field strength ("curvature", but lets not be too technical for now ) is zero.

This is tied into the fact that there is no canonical choice of time + space for space-time.

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Time dilation is a result of an area's particular gravitational strength and dependent on an object's velocity and the rate of which time passes in accordance to general relativity, which is why you would age quicker when stationed on the ground and age much slower when higher in the atmosphere or flying at high speeds. It is the constancy of the speed of light that would keep them intertwined.

I don't really see how that answers my question - is it a "no"? Note that I was not asking what time dilatation is.

Btw.: I think the time dilatation effect is stronger when deeper inside a gravitational field, not weaker.

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We can measure distance (space) with a ruler, which is a static device. But to measure time, we need a dynamic device like a clock, which uses energy. Although space-time may be integrated, a difference between these two variables, is energy is needed to measure time.

This suggested to me that time has a connection to energy. This is easy to see with velocity and special relativity, since we need to add energy to create velocity before we can manipulate time. Or kinetic energy can create time dilation. With gravity, the time dilation is a function of mass density, which according to Einstein relates to energy via E=MC2. Since time has this energy association this would make time the lead variable with space sort of its side-kick. In other words if we manipulate time distance will follow, but if we manipulate distance time does not always follow; quantum jump maintains time.

Edited by pioneer
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We know how to model time, we know how to use it in classical and quantum mechanics. We know how to describe time in special and general relativity. However, I don't think you will find a real convincing explanation of what time is. To a large extent I think we should not spend too much time on this question as understanding how to model and use time is more important.

I agree. What time is (or what energy is or what momentum is) are metaphysical questions. At some level, it's bookkeeping which allows us to quantify what's going on around us. These are the useful parameters since they can be measured and have some use to us.

We can measure distance (space) with a ruler, which is a static device. But to measure time, we need a dynamic device like a clock, which uses energy. Although space-time may be integrated, a difference between these two variables, is energy is needed to measure time.

The rotation of the earth doesn't "use" energy, per se, and is used to measure time. It has energy, but then, so does a meter stick.

This suggested to me that time has a connection to energy. This is easy to see with velocity and special relativity, since we need to add energy to create velocity before we can manipulate time. Or kinetic energy can create time dilation. With gravity, the time dilation is a function of mass density, which according to Einstein relates to energy via E=MC2. Since time has this energy association this would make time the lead variable with space sort of its side-kick. In other words if we manipulate time distance will follow, but if we manipulate distance time does not always follow; quantum jump maintains time.

For that to be true one must expect that a charged particle held in a strong electric field would feel time dilation. I don't know of any theoretical framework which would lead to this, nor any experimental evidence to indicate that it's true.

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To a large extent I think we should not spend too much time on this question as understanding how to model and use time is more important.

I disagree. We should spend more time on understanding Time. It is a missing key.

And the real understanding of Time is not metaphysical. It is Physics 100%.

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I don't really see how that answers my question - is it a "no"? Note that I was not asking what time dilatation is.

Btw.: I think the time dilatation effect is stronger when deeper inside a gravitational field, not weaker.

The location of which time passes is affected by the strength of a gravitational field, when weaker it is more dilated because of the relative speed or rate of two moving objects to two observers as well as their location near a gravitational mass. Space and time become inseparable due an object's velocity or strength of a gravitational field relative to an observer. I am not sure how to make it anymore clearer....

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The location of which time passes is affected by the strength of a gravitational field, when weaker it is more dilated because of the relative speed or rate of two moving objects to two observers as well as their location near a gravitational mass. Space and time become inseparable due an object's velocity or strength of a gravitational field relative to an observer. I am not sure how to make it anymore clearer....

An object deeper in a gravitational well will feel more dilation. It's not the strength of the field.

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An object deeper in a gravitational well will feel more dilation. It's not the strength of the field.

The only thing that has been proven is that as gravity increases frequency reddens given a source.

Now, we use clocks based on frequency. So, naturally as gravity increases these "clocks" beat slower.

Your logic works iff time will only be measured by light frequency and all other measurements are false.

I doubt all will agree in this.

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An object deeper in a gravitational well will feel more dilation. It's not the strength of the field.

Yes it is, the deeper an object is to a larger gravitational mass, by the greater gravitational potential and acceleration. In accordance to general relativity in particular, any kind of g-load contributes to gravitational time dilation.

Edited by Serena2003
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Yes it is, the deeper an object is to a larger gravitational mass, by the greater gravitational potential and acceleration. In accordance to general relativity in particular, any kind of g-load contributes to gravitational time dilation.

Strength of field is the local value for g, which is GM/r^2. The gravitational potential, which tells you the extent of the dilation, is GM/r. With the proper choices of M and r you can have earth's acceleration, but a larger or smaller amount of time dilation. (e.g. by doubling or halving r and changing M by a factor of 4, you can double or halve the potential with g still at 9.8 m/s^2)

The only thing that has been proven is that as gravity increases frequency reddens given a source.

Now, we use clocks based on frequency. So, naturally as gravity increases these "clocks" beat slower.

Your logic works iff time will only be measured by light frequency and all other measurements are false.

I doubt all will agree in this.

Myriad demonstrations of time dilation have been quantitative, so it's much more than saying increasing gravity reddening the source.

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