[geordief (OP)]

Or is it experimentally verified (based on a correct hunch)?

Plus the same question with respect to  the unification of  space and time.

[Halc]

Or is it experimentally verified (based on a correct hunch)?

It seems to be both.  You did not make it clear what said 'first principles' are, but time dilation follows directly from the constant speed of light, which was something observed, not just a principle.
So it is rigorously predicted from that observation.

Plus the same question with respect to  the unification of  space and time.

Time dilation works in models both with and without unification of time and space, so it doesn't depend on it.  To my knowledge, no falsification test has been devised for one model or the other.

[PmbPhy]

Or is it experimentally verified (based on a correct hunch)?

Plus the same question with respect to  the unification of  space and time.

Its predicted by the two principles of special relativity. See the derivation at
http://www.newenglandphysics.org/physics_world/sr/time_dilation.htm

[geordief (OP)]

It seems to be both.  You did not make it clear what said 'first principles' are,

Because  I don't have a firm grasp or grounding myself.I might instead  have asked "Is time dilation rigorously predicted from any first principles?"

I wonder if it is possible to acquire an intuitive feel for time dilation (since it is in accordance with experimental evidence I imagine it must  simply come with closer acquaintance with the phenomenon- I have already heard something like that. )

[geordief (OP)]

Or is it experimentally verified (based on a correct hunch)?

Plus the same question with respect to  the unification of  space and time.

Its predicted by the two principles of special relativity. See the derivation at
http://www.newenglandphysics.org/physics_world/sr/time_dilation.htm

Thanks.I'll take a look.

[chrisdsn]

It was predicted first, but since has been experimentally verified. In fact, we rely on it every day: gps calculations rely on time dilation calculations to be correct. The satellites that send the GPS signals are moving so fast -- and are so high up -- that time dilation from both special and general relativity needs to be taken into account so your phone can tell you where you are.

[PmbPhy]

It was predicted first, but since has been experimentally verified. In fact, we rely on it every day: gps calculations rely on time dilation calculations to be correct. The satellites that send the GPS signals are moving so fast -- and are so high up -- that time dilation from both special and general relativity needs to be taken into account so your phone can tell you where you are.

Its verified every day in particle accelerators. It was first verified by muon lifetime dilations.

[AndroidNeox]

The time dilation of general relativity can be predicted correctly from first principles (universality of c, conservation of energy, Einstein-Planck relation, and causality).

A light beam generated at a source in space stationary with respect to a gravitational mass and shone down toward the mass will be blueshifted. This is because it is traveling from a point of higher gravitational potential energy, GPE, to one of lower GPE. This means an observer lower in the gravity well will see the light as having a higher frequency. But, the number of light waves reaching the lower observer is identical to the number of light waves generated at the source. So, the same number of light waves pass the lower observer in less time than the time required for them to be produced.

The only way to get this to work is for time to pass more slowly for the lower observer than for the higher observer.

This is how I discovered the Shapiro Delay (I'd never heard of it) and this method yields the correct values for both time dilation and Shapiro delay. It's not surprising such simple models can reveal what's going on since these are the sort of thought experiments Einstein used to produce Relativity in the first place.

[guest4091]

geordief;

I wonder if it is possible to acquire an intuitive feel for time dilation (since it is in accordance with experimental evidence I imagine it must  simply come with closer acquaintance with the phenomenon- I have already heard something like that

The phenomenon of time dilation is most easly introduced via the light clock.
In fig.1, light is emitted from a source ED in a direction p, perpendicular to x, the direction of motion, and reflects from a mirror M a distance d=1, to a detector/counter ED. In fig.2, for the same clock to function, the photon path must have an x and p component. The x component compensates for the motion of the clock at speed v. The p component becomes the active part of the clock. Since the photon speed is constant, its path in any direction generates a circular arc for the 90º between the p axis and x axis. This means the relative photon speed u, along p, equals c*sqrt[1-(v/c)^2] = c/γ, i.e. the clock ticks slower, the faster it moves past an observer. This phenomenon applies to all processes involving light interactions, which includes biological (chemical). Therefore in fig.3 the observer moving with the clock at v, does not detect his local clock as running slow.

lite clock.gif (10.14 kB . 761x464 - viewed 3139 times)