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## Einstein Pedometer App Measures Relative Time Gain148

Posted by samzenpus
from the walking-your-way-to-a-younger-you dept.
cylonlover writes "Among other things, Einstein's theory of special relativity says that as an object's velocity increases, time as experienced by the object will slow down when compared to another object traveling at a lower velocity. This means that a 'relatively' short round trip on a space ship traveling at close to the speed of light would see you arrive home having aged less than those back on Earth. While the greater the velocities involved, the greater the effect, the theory applies to all relative movement. Now there's an iPhone app that will let you know just how many extra nanoseconds you've gained by getting moving as opposed to sitting on your rear end."

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## Einstein Pedometer App Measures Relative Time Gain

• #### I used the extra 300 femtoseconds (Score:5, Funny)

by Anonymous Coward on Monday April 11, 2011 @10:33AM (#35782050)

To beat you guys to first post. Bah!

• #### Re: (Score:3)

Wow a witty and topical first post. My hat goes off to you good sir.
• #### You gained none... (Score:3)

on Monday April 11, 2011 @10:39AM (#35782098) Homepage
It doesn't matter much how the time in your frame of reference relates to times of "stationary" observers; it's still the same amount of time for you.

Of course, the gain (and much larger than nanoseconds) might be there vs. just sitting on your rear end. But it depends greatly on the type of movement, for example whether it involves regular exercise.
• #### Re:You gained none... (Score:4, Funny)

on Monday April 11, 2011 @10:46AM (#35782186) Homepage

It doesn't matter much how the time in your frame of reference relates to times of "stationary" observers; it's still the same amount of time for you.

True! But it does bring the future to you that much quicker. And let me tell you, from my perspective of a person from a few nanoseconds ago, the present-ne-future is an amazing place!

• #### Re: (Score:2)

As a person who is from a few nanoseconds into your future let me just say: wait until you see what happens next!
• #### At which height? (Score:2)

If you climb up a mountain you'll be higher up in the gravity well and time will run faster than for people down below. The app should be integrated with GPS readings to take that into account.

• #### Re: (Score:2)

and what about latitude? You'd have to factor in the relativistic differences between sitting near the earth's axis of rotation and whizzing about at the equator. Surely that speed differential is bigger than your walking speed...

• #### Re: (Score:2)

Not once you take general relativity into account.

The equator is whizzing about faster, but it experiences a weaker gravitational field, and a subsequent decrease in gravitational time dilation.

At sea level, the weaker gravitational time dilation and stronger kinematic time dilation cancel. Although GP is correct in pointing out that altitude must be taken into account.

• #### Re: (Score:2)

This app seems more and more inaccurate, let me know when they fix it.

This way I can use any time I save, looking at this app.

• #### Re: (Score:2)

Considering that at speeds far far far below 1% of light speed, the speed itself is completely irrelevant and only 'acceleration' matters .....

• #### Re: (Score:2)

Considering that at speeds far far far below 1% of light speed, the speed itself is completely irrelevant and only 'acceleration' matters .....

No, this is incorrect. Both the kinematic time dilation and the gravitational time dilation are extremely small, but they are roughly on the same order of magnitude in many situations in ordinary life. E.g., if you're flying on a passenger jet, the size of the two effects differs by less than a factor of 10. Also, it's not acceleration that determines your gravitational time dilation, it's gravitational potential.

• #### Re: (Score:2)

You are mistaken, I did not talk about gravitation, I talked about acceleration. (Gravitation however is also a factor, but was not my topic)

Speed is completely irrelevant as long as it is not close to light speed. It is the acceleration that brought you to that speed, that matters.

angel'o'sphere

• #### Re: (Score:2)

You are mistaken, I did not talk about gravitation, I talked about acceleration. (Gravitation however is also a factor, but was not my topic)

The equivalence principle says they're the same thing.

Speed is completely irrelevant as long as it is not close to light speed. It is the acceleration that brought you to that speed, that matters.

No, this is completely incorrect. There is a small effect when your speed is far below the speed of light. All of the effects we're talking about are small.

You may want to take a look at the classic papers by Hafele and Keating and Alley from the 1970's. A good summary of Alley's work is available here:
In NASA. Goddard Space Flight Center Proc. of the 13th Ann. Precise Time and Time Interval (PTTI) Appl. and Planning Meeting, p. 687-724, 1981 (SEE N82-20

• #### Re: (Score:2)

Then we both have a problem to agree on the word "irrelevant". Irrelevant is the oposite of relevant, it does not mean not existing.

The time delation effects are calculated with a very simple formula: t0 = T * sqrt(1-(v*v/c*c)).

If you enter small speeds like a car moving you see the effect is very very very low.

I never neglected that effect. I only said: it is not really relevant as ACCELERATION is what matters. My grandparant mixed up acceleration with speed.

Speed is completely irrelevant as long as it is

• #### Re: (Score:2)

Thanks for the link, I will dig through it ;D but I fear it might be beyond my last physics class, hehe.

If you want to learn some relativity, the first book I always suggest to people is Gardner, Relativity Simply Explained. You could also try Geroch, Relativity from A to B. At a somewhat higher mathematical level, there is Exploring Black Holes by Taylor and Wheeler, or various upper-division undergrad books like Hartle.

• #### Re: (Score:2)

No, this is incorrect. Both the kinematic time dilation and the gravitational time dilation are extremely small, but they are roughly on the same order of magnitude in many situations in ordinary life. E.g., if you're flying on a passenger jet, the size of the two effects differs by less than a factor of 10. Also, it's not acceleration that determines your gravitational time dilation, it's gravitational potential

FWIW the contribution of gravity is the same as the escape velocity .. on the surface of earth it is about ~7miles/sec.

• #### Re: (Score:2)

Of course, then it would be only decent to also calculate & show different risks of cancer from cosmic radiation (hence expected average differences of available time), or unhealthy effects of low oxygen levels ;P (but yeah, IIRC the differences from going up&down the gravity well are quite on par with those from human-scale speeds of movement)
• #### 22 more nanoseconds (Score:5, Informative)

on Monday April 11, 2011 @11:30AM (#35782790)

There is at least one hobbyist [wired.com] that has measured it by taking a surplus rubidium oscillator up mt. Rainier. "It was the best extra 22 nanoseconds I've ever spent with the kids,"

• #### Philosophical Exercise (Score:5, Informative)

<(deviladv) (at) (gmail.com)> on Monday April 11, 2011 @11:04AM (#35782474) Homepage

The time one lives on this planet is relative to measurements made by other people and by other devices. Your watch on your own wrist is probably the most accurate personal time you can get, but you have to adjust it based on other clocks around you to remain in sync with the rest of the world. Even more so, computers and phones now regularly ping a clock server to get an updated time automatically, and that server is somewhere else, being stationary. Time on the Earth is measured in terms of the velocity of the planet's orbit and rotation, but not in terms of your personal velocity relative to the sun or earth itself. The earth rotates and orbits at a specific velocity. If you move, your velocity relative the sun is different than the planet itself.

However, by moving, based on the theory of relativity, you are gaining a fraction of a fraction of a second by moving faster than the world around you. The clock is a philosophical exercise exploring relativity, and it's not like you'll gain 200 relative years by constantly walking or running anywhere, but it's fun to observe relativity in action. The "gain vs loss" here is that 1 second for you is still 1 second, but if you were say running, 1 second for you is, for example, 1.000000000000000000000000000000000000000000000000000000000000001 seconds for everyone you pass that are standing still. So you gain that fraction of a second relative to the world around you, and thus travel into the future a little faster than others.

• #### Re: (Score:3, Insightful)

No, I'm at rest. Everything else is revolving around me. It's a chaotic dance to be sure, but I'm at the center of it ! :)
• #### Re: (Score:2)

I think that this is the true heart of the twins paradox. Motion induces time dilation, that's easy to understand. Nothing paradoxical about it. However, from the point of view of the "moving" twin, the "stationary" twin is the one that moves, thus each twin sees the other as stationary. Each twin will see time passing more slowly for the other than for themselves. In other words (A<B) AND (B<A) is true.
• #### Re: (Score:3)

No the twin paradox is resolved by noticing that one twin has to accelerate at least twice on his round trip (and thus his frame of reference isn't in an inertial frame of reference and therefore not valid for calculations in special relativity) while the stationary twin doesn't accelerate at all.

• #### Re: (Score:2)

"The time one lives on this planet is relative to measurements made by other people and by other devices."

Not at all. It's the same for everybody and it's as absolute as C: exactly one life.

(unless you belong to one of the religions that allow you to reincarnate, of course).

• #### Re: (Score:2)

It doesn't matter much how the time in your frame of reference relates to times of "stationary" observers; it's still the same amount of time for you

True, but you'll look younger to your peer group. Of course, the effect is negligible -- so the cosmetics and pharmaceutical industries will be marketing this PDQ.

• #### Re: (Score:2)

Like say, flying in an airplane across an ocean will "gain" you more time than you can ever hope to acquire by walking. Not to mention all the time the average human spends driving or being driven at 30-60mph - rendering the use of such a device moot. But still the sedentary frequent flier will not necessarily live longer than the reasonably athletic non flier...
• #### Re: (Score:2)

It doesn't matter much how the time in your frame of reference relates to times of "stationary" observers; it's still the same amount of time for you.

Of course, the gain (and much larger than nanoseconds) might be there vs. just sitting on your rear end. But it depends greatly on the type of movement, for example whether it involves regular exercise.

Can someone explain to me how if I walk around and you stay "still" we aren't moving at the exact same speed relative to one another?

• #### relative to what? (Score:3)

<sdotno@chPARISea ... s.com minus city> on Monday April 11, 2011 @10:40AM (#35782120)

Wouldn't this "gain" depend on which direction you're walking - along with the rotation of the earth, or against it?

Or if you're comparing to non-earthly reference points - along with the revolution around the sun & galaxy or against them?

• #### Re: (Score:2)

Relative to the speed of light. Meaning walking saves you a nearly infinitesimal amount of time.

Theoretically, as you get closer to the speed of light, time should slow down for you. Hence all the mumbo jumbo about a flight to Alpha Centauri taking maybe 50 years, but at that speed it would only be 20 years to the people doing the traveling. Those numbers are no where near accurate, but hopefully you get the idea.

While not an expert in the field, obviously, I myself harbor serious doubts as to the accuracy

• #### Re: (Score:2)

Time dilation is proven to you every time you use a friggin' GPS; a system which wouldn't work without taking the effect into account (also... [xkcd.com])
• #### Re: (Score:2)

You should rest easy! It's been confirmed directly using planes and atomic clocks: http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment [wikipedia.org] as well as in observed ratios in muon detections from cosmic rays and in the operation of particle colliders like the LHC and at Fermilab. Also, interestingly, it is what is ultimately responsible for magnetic fields. The fact that you can stick these things to your fridge is a consequence of time slowing down and space shortening for charges in motion. It's
• #### Re: (Score:3)

You should rest easy! It's been confirmed directly using planes and atomic clocks:

I'm glad those experiments were conducted back in the 70's. If someone thought that up now, well, just imagine what the TSA goons would do if you said the mysterious electronic device in your carry on was an atomic clock.

• #### Re:relative to what? (Score:5, Interesting)

on Monday April 11, 2011 @11:12AM (#35782588)

It isn't just about math. These effects have been proven experimentally - just not by sending a human off to Alpha Centauri. Follow the references for more relativity fun. [wikipedia.org] I personally find length dilation to be the most interesting and difficult to get my head wrapped around.

Fun thought experiment:

A 100m rocket speeds toward a 90m hangar building at .99C. As the rocket passes through the open doors of the hangar the operators of the building close both sets of doors while the rocket is entirely inside the building. This is possible because of the length dilation happening at the high relativistic speeds (the rocket is compressed to less than 90m from the view of the hangar).

But from the point of view of the ship, it is the hangar that is approaching at .99c. Therefore the hangar is foreshortened - even shorter than 90m - leaving more than 10m too much rocket hanging out. What do each of the door operators and the pilot of the rocket see happening?

This is a fun use for all that math you learned to figure out relativity. Even though both frames of reference see things in entirely incompatible ways, both versions of the truth are entirely consistent via relativity.. Fun!

• #### Re: (Score:2)

Well then, thanks for all the responses showing how wrong I am >_.

Its something that has never stuck well with me however. I believe that with the evidence its probably(99.9e10^20 %) right, but won't be terribly surprised if they discover some other weird QM effect or something that causes the evidence to appear like what we think should confirm the theory. Basically I'm cynical about it. So sue me.

All the rest of that stuff is really cool though. Never knew the thing about the magnetic effect. Wouldn't

• #### Re: (Score:2)

hopes for links explaining exactly what gravity is

That's a vain hope, nobody knows what gravity is [youtube.com], same goes for the other fundemental forces. Like time and space they can't be defined without self-reference.

• #### Re: (Score:2)

Considering that Alpha Centauri is only 4 light years away, from an outside observer you would accelerate 100 days, and decelerate 100 days and fly like 3 years and 10 monthes + 200 days (acceleration + deceleration) but from your point of view it would be only 200 days (acceleration + deceleration) + a few weeks at close of speed of light.

Well, you don't need to know anything about relativity, no one really expects that.

But that alpha centauri is the closest star to our sun, THAT you perhaps should know. A

• #### Re: (Score:2)

That would be traveling AT the speed of light.

I'm aware of the 4 light year distance, but currently with top end projected attainable speeds from what I understand the trip will still be better measured in decades than years.

Even 50 years means traveling at an appreciable fraction of the speed of light.

• #### Re: (Score:2)

Ah, sorry my fault ;D

But 50 years is not a *noticeable* fraction of the speed of light, it is a 1/10th at best, there is no real time delation effect. (Ofc you can measure it with good clocks but I doubt it is in the range of an hour even)

angel'o'sphere

• #### Re: (Score:2)

The effect stems from relative differences in speed of object in question vs. chosen frame of reference, it essentially (*) doesn't matter "in which direction you spin" or other scifi mumbo-jumbo ( * it sort of might when you take into account how the space itself is being dragged by rotating object, particularly a massive and compact one)
• #### Re: (Score:2)

no.
The article very poorly described the way relative velocity works.

While moving relative to another object/person, time slows for you relative to that object/person, not relative to all of space/time. When you return, you are in their future. Time dilation relating to the Sun/Earth/Galactic center are all different depending on your velocity in relation to those objects.
So, for example, if there are 3 people, 1 remains at rest on earth, the 2nd travels away at 25% the speed of light, and a 3rd travels in
• #### Re: (Score:2)

The problem is that the article is a little bit wrong. In special relativity lets say I'm sitting next to someone and then I go for a walk and come back. When we compare clocks they will be the same since otherwise there would be symmetry breaking and we could establish a preferred inertial frame. Now in general relativity the symmetry is broken by the bending of time caused by my acceleration and when I return to my desk I will be younger than my stationary friend. i.e. this is all a consequence of gen

• #### Re: (Score:2)

In special relativity lets say I'm sitting next to someone and then I go for a walk and come back. When we compare clocks they will be the same since otherwise there would be symmetry breaking and we could establish a preferred inertial frame.

You don't need to factor in acceleration to have the clocks get out of sync, just remember that changing directions means you won't be at rest the whole time in any reference frame:

Inertial frame of your friend: First you move away with say 1 m/s. Halfway through yo

• #### Re: (Score:2)

No. It depends on whether you accelerate or not. If you fly around the planet at a particular speed you'll experience less time than someone left behind. It doesn't matter which direction you go. Since the planet, solar system, galaxy etc. are all in inertial reference frames, their relative rate of time is not affected by their relative velocities.

• #### Re: (Score:2)

Wouldn't this "gain" depend on which direction you're walking - along with the rotation of the earth, or against it?

Assuming both people are on earth it would NOT matter which direction realitive to the other or rotation of the earth they were moving. If they were going 100 mph twoard you or 100 mph away from you the effect is exactly the same.

However there is a problem in that the person who gets in their cars or starts walking their realitive velocity is the one in the accelerated frame realitive to the person standing still. So references only work against fixed features like Micro\$ft HQ unless both people run the a

• #### Badly named (Score:5, Funny)

by Anonymous Coward on Monday April 11, 2011 @10:46AM (#35782184)

It's actually a pedantometer.

• #### Re: (Score:2)

Dammit, I pointed my pedantometer at your post and it exploded.

• #### Re: (Score:2)

It should really be called a pedometric pedantochronograph.

• #### Re: (Score:2)

Speaking of "badly named," pedometer sounds like something made up on 4chan to rate the age of children in image posts.
• #### You LOSE time not gain it. (Score:5, Informative)

on Monday April 11, 2011 @10:46AM (#35782194)
Think of it this way: Two guys have a deadline in an hour. Guy #1 sits at his desk and does nothing. Guy #2 zips around at a high velocity and returns to meet guy #1. Both guys check their watch, guy #1 notes an hour has past, while guy #2 notes that half an hour has past. Although guy #2 has aged less, he actually had less time to work to meet the deadline. In the spirit of the original post, guy #2 has lost time instead of gained it.
• #### Re: (Score:2)

Maybe that's why exercise extends life. They don't really live longer, it's just that their 60 year old body has only experienced 59 or whatever.

• #### Re: (Score:2)

The treadmill companies aren't going to like the sounds of this.

• #### Re: (Score:2)

Exactly, you are behind the times due to time dilation, it only lets you watch the world zoom past.
• #### Re: (Score:2)

That's because you're doing it wrong: if you have a deadline in an hour, what you should do is to put your boss in a spaceship travelling at near light speed, not go in it yourself.

Ok, the App is very minimal, just tells you how much time you've gained(?) compared to a "stationary" observer.

The info panel allows you to put in your birth date. Presumably this is to show you how much time you've added to your life? (It also allows you to turn on multi-tasking for the app so I guess it can constantly determine how much time you've saved).

I wish it would give a little more info (ideally a running graph showing time slowing down as you're speeding up). It says it uses GPS but I'm assumi

• #### Re: (Score:2)

(It also allows you to turn on multi-tasking for the app so I guess it can constantly determine how much time you've saved) ... It says it uses GPS but I'm assuming it isn't calculating how much time is speeding up if you climb up some stairs

• #### Re: (Score:2)

...For that matter I assume it isn't taking into account acceleration (note to physicists: does non-gravity acceleration cause time dilation?).

Still it is free, and makes me feel very very very slightly younger!

IAAP (I am a physicist), so I can confirm that non-gravitational acceleration causes time dilation, under some circumstances. Since I'm waiting for some calculations to finish running through Mathematica, I'll also try to explain. :-)

Non-gravitational acceleration does cause time dilation, at least when viewed in the frame of the accelerated observer. When analyzed in the frame of an inertial observer (read: if someone who isn't accelerating calculates how much time has passed for you based on how you a

• #### Re: (Score:2)

Thank you very much!

• #### Saving silicon (Score:2)

Does this mean that the faster I run my CPU, the longer it will last?

• #### Something I've never understood (Score:2)

If motion is relative, how does the universe know which of us is moving in the near-light-speed vehicle so that person's clock runs slower than the stay-at-home's? We're both moving relative to each other.

• #### Re: (Score:2)

how does the universe know which of us is moving in the near-light-speed vehicle so that person's clock runs slower than the stay-at-home's?

The person who traveled accelerated to change his relative speed.

If you travel to a distant planet and get back, you will have accelerated to near light speed, braked down, accelerated back again, and braked down to get back to your twin's side, while he was at rest all the time.

However, if you travel to a distant planet, and then your twin follows you there, you will both have the same age in the end, because you suffered the same accelerations.

• #### Re: (Score:2)

Actually, acceleration has nothing at all to do with the twin paradox, insofar as it is explained by special relativity, which does not address acceleration. It would work the same way if, for instance, an object passed by earth at relativistic speeds, moved out a distance x, passed its clock measurement on to a second moving objecting moving in the exact opposite direction, which then compares its clock to one sitting on Earth and finds that less time has gone by.

My confusion, of course, comes from wha
• #### Re: (Score:2)

There are time dilation effects from acceleration alone, independent of speed. This can be proved by a thought experiment: imagine you are at the rear end of an accelerating car. At the front end a light flashes exactly once per second. According to your measurements, the flashes occur at shorter intervals than one second, because between each pair of pulses you are moving faster than between the former pair.

Note that this has nothing to do with Lorenz time dilation, since you and the clock are always movin

• #### Re: (Score:2)

That's nice, but the Twin Paradox put in terms of three moving bodies as I described above avoids any acceleration at all in the course of the thought experiment, so general relativity and acceleration dilation are a non-issue.
• #### Re: (Score:2)

Doppler shift of the cosmic background radiation. If you're stationary, the background radiation is the same "color" in every direction. If you're moving, it is blue shifted in the forward direction, and red shifted in the backward direction.
• #### Re: (Score:2)

Using uniform background radiation as a privileged inertial frame is cheating. Who is to say that the source of that radiation wasn't just moving fast enough to cause a blue shift equal to what I see while I am walking to keep pace with the rest frame, and the uniform color you see isn't the result of matching your velocity to that of the cosmic background radiation's moving inertial frame?
• #### Calculates, not measures. (Score:3)

on Monday April 11, 2011 @11:05AM (#35782496)

Measuring would just a tad more difficult...

• #### Oh great (Score:2)

Next stop: add leap nano-seconds to NTP.
• #### How fast are we going? (Score:2)

If everything is relative, wouldn't we need to know what is relevant? The earth rotates and revolves around the sun while the sun revolves around the galaxy while the galaxy moves through the universe. That is a lot of movement. Relative to the center of the universe, the one who moves fastest might be the one who sits still. More importantly, the relative difference in momentum between any two of us might be infinitesimal when compared to the whole. Nanoseconds might seem like millennia by comparison.
• #### Re: (Score:2)

Considering movement is relative, the momentum and vector of motion of the Earth does not matter. You want to compare your time dilation to the Earth's, you don't need more than those two frames of reference.

Obviously, there's the problem that the Earth is not an inertial frame of reference (since it is accelerated), and that likewise you are not an inertial frame of reference even when assuming that the Earth is (since you are on its surface, which is spinning), so you'd need to do some fairly complex gene

• #### The Flash! (Score:2)

So in reality the Flash should be relatively (pun intentional) immortal compared to the rest of us.

To really bend you bonnet out of shape, so while he is vibrating so fast as to go back in time, that would be relativistically speaking the rest of the world would be moving forward in time at a faster rate.

Also

The Flash would kick Superman's ass in a race... :)

• #### I need the related "red shift" app (Score:2)

That would help warn me when an apparently green traffic signal was actually red to a stationary observer. Talk about savings. This beats extra nanoseconds by a . . . uh . . . it beats them!
• #### what a lot of BS (Score:2)

If you could walk fast enough to make a difference, your body would wear out real fast.

Sure they have measured time differences in atomic clocks that have traveled on jet planes, but imagine the stress on your joints and bones if you could walk at 600mph, not to mention the likelyhood of having an accident (most people can barely cope with car driving speed in terms of reaction abilty..

Somebody mentioned (DC comics) The Flash. How come he doesn't burn up from the heat of air resistance?

• #### Re: (Score:2)

Somebody mentioned (DC comics) The Flash. How come he doesn't burn up from the heat of air resistance?

The explanation is that the Speed Force (an extradimensional force that these characters somehow tap into) causes an aura to appear around them as they are running, protecting them from friction and minor harm.

• #### Earth moving (Score:2)

Am i the first to question whether this includes the earth rotation?

Besides, when talking about general relativity and moving, can't we determine the exact a centre of our universe by finding the spot (mass points excluded) that (relatively speaking) has the greatest time-dialation potential for any trip in the vacuum of space?

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