If anyone here doesn't yet get the twin "paradox". .

In summary, Jim al Khalili did a (basic level) TV programme in the UK last night where he featured a smartphone app which works as a space-time "odometer". The app's page doesn't say how it works, but I'm assuming it uses some combination of accelerometer/GPS to sense your velocity and altitude and then calculates your time dilation factor relative to a standard (the usual standard is being at rest on the Earth's geoid), and integrates that to get your elapsed aging. From what he said in the programme I think he worked out the SR and GR effects separately. Interesting. The app's page doesn't say how it works, but I'm assuming it uses some combination of accelerometer/
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Jim al Khalili did a (basic level) TV programme in the UK last night where he featured a smartphone app which works as a space-time "odometer".

Now you can experiment on your own version of the legendary brain-teaser with your friends, no need to go to Alpha Centauri and back! Go for a walk, take a bus/tube ride, or just sit in an armchair - the choice is yours.
 
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Interesting. The app's page doesn't say how it works, but I'm assuming it uses some combination of accelerometer/GPS to sense your velocity and altitude and then calculates your time dilation factor relative to a standard (the usual standard is being at rest on the Earth's geoid), and integrates that to get your elapsed aging.
 
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If this encourages people to move around quickly to get reduced aging from relativity, it will give a much larger benefit from biological 'age reduction'; of course, if a car is used, not so much.
 
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  • #4
The gravitational effect dominates unless you use an airplane or drive around all day.
 
  • #5
mfb said:
The gravitational effect dominates unless you use an airplane or drive around all day.
Ah, but the gravity effect is the common baseline. You are not going to change anything by jumping (unless you can jump like a flea), most people fly only a couple times per year. Thus, motion is the controllable factor.
 
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Unless you live in an extremely flat region, just changing the position will change your height a bit, changing the gravitational time dilation.
Even going one floor up or down has an effect of 0.3 fs/second or 26 ps per day.
 
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mfb said:
Unless you live in an extremely flat region, just changing the position will change your height a bit, changing the gravitational time dilation.
Even going one floor up or down has an effect of 0.3 fs/second or 26 ps per day.
ah, good point. For a longer life (relative to others) get thee to Death Valley!
 
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I don't think that is good for your health, and it is not particularly deep (down to 86 m below sea level). Go to the Dead Sea (430m below sea level).
You can also go into mines, but that is probably even worse in terms of health and you don't have GPS there - the app won't work.
 
  • #9
mfb said:
I don't think that is good for your health, and it is not particularly deep (down to 86 m below sea level). Go to the Dead Sea (430m below sea level).
You can also go into mines, but that is probably even worse in terms of health and you don't have GPS there - the app won't work.
I LOVE desert hiking. Two of my best hiking memories are hiking all day solo in Death Valley in October, and hiking with buddy during cactus blooming season in the Sonoran desert.

Edit: but I'm sure I'd like the Dead Sea!
 
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  • #10
mfb said:
You can also go into mines, but that is probably even worse in terms of health and you don't have GPS there - the app won't work.
But if you were in a (well air conditioned) sphere in the exact center of the Earth, wouldn't be weightless?
 
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Chris Miller said:
But if you were in a (well air conditioned) sphere in the exact center of the Earth, wouldn't be weightless?
Yes, but time dilation relative to sea level would be maximal. To make a simplistic analogy, the more stair climbing energy you need to reach distant empty space, the slower you age relative to distant empty space. Acceleration of gravity at one point plays no role at all in gravitational time dilation.
 
  • #12
PeterDonis said:
Interesting. The app's page doesn't say how it works, but I'm assuming it uses some combination of accelerometer/GPS to sense your velocity and altitude and then calculates your time dilation factor relative to a standard (the usual standard is being at rest on the Earth's geoid), and integrates that to get your elapsed aging.
From what he said in the programme I think he worked out the SR and GR effects separately. Interestingly, he got it wrong the first time (he did not realize the surface of the Earth is equipotential) during the making of the programme, and had to get it re-done!
I think the current version is more sophisticated as a result, somewhere I read that it now also includes the Sagnac effect.

It seems a good time to bring up this article again for those interested in the gory details.

[EDIT] Here is a link to a review of the programme.
 
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1. What is the "twin paradox" in science?

The twin paradox, also known as the twin paradox of time dilation, is a thought experiment in physics that explores the concept of time dilation in Einstein's theory of relativity. It involves two twins, one of whom remains on Earth while the other travels at high speeds to a distant location and back. When the traveling twin returns, they have aged less than the twin who remained on Earth.

2. How does time dilation work in the twin paradox?

According to Einstein's theory of relativity, time is relative to the observer's frame of reference. When an object moves at high speeds, time slows down for that object. In the twin paradox, the twin who stays on Earth is in a relatively stationary frame of reference, while the traveling twin is moving at high speeds. This causes time to pass at a slower rate for the traveling twin, resulting in them aging less than the twin on Earth.

3. Is the twin paradox a real phenomenon or just a thought experiment?

The twin paradox is a thought experiment used to illustrate the concept of time dilation in Einstein's theory of relativity. While the effects of time dilation have been observed in experiments involving atomic clocks, the twin paradox itself cannot be replicated in real life as it would require a person to travel at speeds close to the speed of light.

4. Can the twin paradox be explained in simpler terms?

In simpler terms, the twin paradox can be understood as a difference in the passage of time for two objects in different frames of reference. The traveling twin experiences time at a slower rate due to their high-speed motion, resulting in them aging less than the stationary twin on Earth.

5. Are there any real-life examples of the twin paradox?

While the twin paradox cannot be replicated in real life, there are other phenomena that demonstrate the effects of time dilation, such as the synchronization of atomic clocks on satellites in orbit. These clocks run slightly slower due to their high speeds and the effects of gravity, resulting in a small time difference compared to clocks on Earth.

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