# A vine's age

1. Nov 25, 2015

### butchie

It has been given as proof that time speeds up at higher altitudes because of the decrease in gravitation demonstrated using atomic clocks. If this is true how tall would a vine have to grow to have the tip be older than the stump? I suggest the whole concept must be wrong that suggests an impossibility such as this. Perhaps something is being overlooked in the functioning of the clocks operating under differing environments (gravitational field strength). I've read such authors as Hawking suggesting distortion of time but I am silly enough to believe that now is now everywhere.

2. Nov 25, 2015

### Staff: Mentor

Strictly speaking, the tip is older as long as it's higher by any amount. A better question would be, how much older is the tip than the stump for a given height of vine in a given gravitational field? For a 10-foot high vine on Earth, the answer is, about one part in $10^{-15}$ older.

Why do you think it's a impossibility? Any extended object, like a vine, does not have to have a single "age".

Then you believe something that contradicts relativity. That is not a good strategy.

3. Nov 25, 2015

### Staff: Mentor

Hi butchie, welcome to PF!

Please explain what makes you think this is impossible. To me it is clearly not impossible, so I am not sure what leads you to believe it.

4. Nov 26, 2015

### Mister T

It'll never happen. The effect cannot precede the cause. This is a principle known as causality and there's no law of physics that violates it. I'm not fluent in general relativity so I cannot explain the details. In special relativity the explanation lies in the invariant speed of light. If you signal faster than light there would be frames of reference where the effect would precede the cause. Such a thing is silly.

I have never known a person to accept the relativity of simultaneity immediately upon hearing of it. (Anyone appearing to do so is not engaged.) Evidence from lots of things besides just atomic clocks tells us that "now everywhere" is just not a valid notion. Moreover, detailed examination of the theories that explain it make it a perfectly plausible notion. There is overwhelming experimental evidence to support it.

No one has come even close to putting forth a theory that preserves absolute simultaneity and accounts for the vast array of experimental evidence in a wide variety of areas from cosmology to electromagnetism to electronics to optics to particle physics, to name just a few.

5. Nov 26, 2015

### Staff: Mentor

I don't think the OP is talking about violating causality; he's just talking about the fact that different parts of an object that are at different altitudes in a gravitational field will age at different rates. There's no causality violation in that.

I don't think the OP is talking about relativity of simultaneity either. The different rates of aging of objects at different altitudes in a gravitational field are all evaluated relative to a common standard of simultaneity, since the objects are all at rest relative to each other. I think what the OP is struggling with is the counterintuitive fact that objects (or parts of objects) at rest relative to each other, all sharing the same standard of simultaneity, can still age at different rates if they are at different altitudes in a gravitational field. In other words, sharing a standard of simultaneity does not necessarily imply aging at the same rate.