Cosmology: Einstein general theory time is relative (Introduction)

by David Turell , Tuesday, April 12, 2022, 18:39 (746 days ago) @ David Turell

Depends on motion and gravity:

https://bigthink.com/starts-with-a-bang/time-dilation/?utm_source=mailchimp&utm_med...

"No matter where you are in the Universe, time always passes at precisely the same rate for any observer: one second per second. But when it comes to how time passes at one location relative to another, both your speed and how deep inside a gravitational potential well you are affect the rates at which clocks run. As a result, there not only is no absolute time, but time passes faster at higher elevations on Earth than lower ones. From space to mountaintops to tabletops, we've measured the difference, and Einstein had it exactly right.

***

"...if you have two different clocks, you can compare how time flows under different conditions. If one clock remains stationary while the other travels quickly, the fast-moving clock will experience a smaller amount of time passing than the stationary clock: that’s the rule of time dilation in special relativity.

"What’s even more counterintuitive, however, is that the relative flow of time also depends on the difference between how severely space is curved between two locations. In General Relativity, this corresponds to the strength of gravity at your particular location, which means that your feet actually age at a different rate than your head when you’re standing up. Here’s the physics of how we know.

***

"...the laws of physics remain the same at all times and all places, and so these transitions that emit or absorb photons always occur at the same energy. However, if the emitter of a photon and the (potential) absorber of a photon aren’t located at the same time and place as one another, there’s a good chance that they won’t agree on the energies they observe.

When it’s because the objects are in relative motion with respect to one another, we know this effect as a Doppler shift.

***

"...here’s where things get weird: this same type of shift should also occur — even if everyone is stationary — when your gravitational field strength changes from one location to another.

***

"Just as you can have Doppler redshifts and blueshifts for light, you can also have gravitational redshifts and blueshifts. For example, if you send a photon from the Sun to the Earth, because the Sun’s gravitational field dominates the Solar System and is stronger near the Sun than farther away, that photon will lose energy (and become “redder”) as it travels from the Sun to the Earth. If it were to go in the opposite direction, from the Earth to the Sun, the photon would gain energy and become “bluer” in color.

***

"The overall lesson is this: for every meter of height that you gain, you need a Doppler shift of ~33 nanometers-per-second to compensate for it. It’s like being lower on the surface of the Earth requires you to be in motion at a certain rate just to have time pass at the same rate as it would if you were higher. In other words, without an extra little speed boost at your feet — without an extra amount of time dilation added in — time passes more quickly at higher elevations in Earth’s gravitational field.

"Your head, to be blunt, ages more quickly than your feet do."

Comment: God made our world counterintuitive in relativity and quantum mechanics. And folks like dhw wish to analyze God and outthink Him, complaining about what He has created and the way He did it, ignoring the factual history God created along the way. We have only a smidgeon of His mental capacity. We cannot fathom those depths.