1 Ed Lake | A suggested time dilation experiments | Sunday 15 July 2018 |

2 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

3 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

4 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

5 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

6 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

7 JanPB | Re :A suggested time dilation experiments | Monday 16 July 2018 |

8 Prokaryotic Caspase Homolog | Re :A suggested time dilation experiments | Monday 16 July 2018 |

9 Thomas 'PointedEars' Lahn | Re :A suggested time dilation experiments | Monday 16 July 2018 |

10 Prokaryotic Caspase Homolog | Re :A suggested time dilation experiments | Monday 16 July 2018 |

11 Ed Lake | Re :A suggested time dilation experiments | Monday 16 July 2018 |

12 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

13 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

14 tjrob137 | Re :A suggested time dilation experiments | Monday 16 July 2018 |

A suggested time dilation experiment

673 posts by 38 authors

https://groups.google.com/forum/?fromgroups=#!topic/sci.physics.relativity/HSKOJoUnvy0[101-125]

On Sunday, July 15, 2018 at 2:59:48 PM UTC-5, hallst...@gmail.com wrote:

> | On Sunday, July 15, 2018 at 10:02:34 AM UTC-7, Ed Lake wrote: |

> > | If they can tell the difference in tick rates for an atomic clock that is just 1 foot higher than another atomic clock... |

> |
But they can't. The measurements of differences in gravitational potential for extremely small differences in elevation are not performed by comparing the tick rates of ordinary cesium clocks, they are performed by means of things like the Mossbauer effect and redshift/Doppler measurements - the very kinds of measurements you reject. |

The NIST used aluminum based atomic clocks: https://www.nist.gov/news-events/news/2010/09/nist-pair-aluminum-atomic-clocks-reveal-einsteins-relativity-personal-scale

> |

> > |
At 1G I weigh 160 pounds. At 2Gs I weigh 360 pounds. At 3Gs I weigh 540 pounds. Etc. At 20Gs I would weigh 3,200 pounds. And you think it would not require any more work to lift 160 pounds than 3,200 pounds? Really? |

> |
You're confusing work and force. Work is defined as the amount of force multiplied by the distance through which the force is applied. It takes twice as much work to lift a 1 lb object 10 feet than it takes to lift it just 5 feet. In the NASA centrifuge a 1 lb object would weight 20 lbs (maximum), and you have to lift it 29 feet, so that is 580 ft-lbs of work. Compare this with the Hafele-Keating experiment, where a 1 lb mass would only weight about 1 lb, but you have to lift it 30,000 ft, so that is 30,000 ft-lbs of work. |

You are not understanding the experiment. It is not about lifting objects. It is about gravitational TIME DILATION. At ground level a clock ticks at a given rate. One foot higher than that and the clock ticks at a faster rate. The centrifuge simulates gravity. Einstein's equivalence principle says simulated gravity works the same way to slow time as real gravity.

> |
So the Hafele-Keating experiment has over 50 times as much gravitational time dilation as the NASA centrifuge. |

Nonsense. At 30,000 feet someone who weighs 160 pounds on the ground would probably still weigh 159.999 pounds. But a person who weighs 160 pounds at 1G will weigh 3,200 pounds at 60Gs.

> |

> > |
Evidently, the textbooks are about different speeds along different points along the centrifuge arm, NOT about comparing gravitational and velocity time dilation at the end of the centrifuge to time shown by a clock that is NOT ON the centrifuge. |

> |
That's not true at all. Take a look at the discussion of the centrifuge in Misner, Thorne, Wheeler textbook on general relativity. |

Okay. It's titled "Centrifuge and the Photon" and it begins on page 63. The word "dilation" is not used. It has absolutely nothing to do with time dilation.

> | The predi... |

On 7/15/18 11:48 AM, benj wrote:

> | Actually the problem is that it depends on the clock used. Theory shows that while some electromagnetic clocks slow exactly as relativity predicts, others do not. |

This is just plain not true: * SR/GR predicts "time dilation" is EXACTLY the same for all clocks, because it is a geometrical projection between inertial frames, which has NOTHING WHATSOEVER to do with any clocks. * SR/GR predicts the difference between elapsed proper times for different paths is EXACTLY the same for all clocks, because it is a difference in path length, which has NOTHING WHATSOEVER to do with any clocks. That is, these effects are GEOMETRY, which is exactly the same for all types of clocks.

What "theory" are you alluding to? References, please.

> | The bold assumption of science is that ALL clocks act the same. |

Hmmm. It was bold in 1905, and even in 1916. Today it is old hat, because it is predicted by SR and GR (which are among the best-tested theories we have), and because literally zillions of experiments confirm it.

The decays of unstable leptons and hadrons all behave as SR/GR predicts, as do the atomic clocks of the GPS. These use tim... Show trimmed content

On 7/15/18 12:02 PM, Ed Lake wrote:

> | You misunderstand the experiment. If they can tell the difference in tick rates for an atomic clock that is just 1 foot higher than another atomic clock, where the difference in gravity is something like 1G versus 0.9999999995Gs, then they certainly can tell the difference in clock tick rates when one clock is subjected to 1G while a clock nearby is subjected to 20Gs. |

But "they" cannot perform an experiment -- that requires real people, not your unspecified pronoun.

The clocks you allude to will not fit into the centrifuge, and will not operate at 20 g.

> | On Saturday, July 14, 2018 at 8:17:56 PM UTC-5, hallst...@gmail.com wrote: |

>> | Also, time dilation is NOT due to difference in acceleration or weight, it is proportional to the amount of work needed to lift an object from one location to the other. The centrifuge has 20g acceleration at the end, but the arm is only 29 feet long, so it wouldn't take much work to "raise" an object from the end to the center (where there is no centrifugal time dilation at all). By comparison, in Hafele-Keating there is only about 1g acceleration but the planes are over 30,000 ft up, so the work to lift an object is FAR greater. That's why the time dilation in Hafele-Keating is MUCH greater than for this centrifuge. |

> |
At 1G I weigh 160 pounds. At 2Gs I weigh 360 pounds. At 3Gs I weigh 540 pounds. Etc. At 20Gs I would weigh 3,200 pounds. And you think it would not require any more work to lift 160 pounds than 3,... |

On 7/15/18 3:50 PM, Ed Lake wrote:

> | It is about gravitational TIME DILATION. [...] |

If you want to measure gravitational "time dilation", then you must perform an experiment that depends on it. The centrifuge does not.

SPINNING IS NOT GRAVITATION.

Tom Roberts This message has been deleted.

On 7/15/18 12:27 PM, Ed Lake wrote:

> | On Saturday, July 14, 2018 at 10:30:43 PM UTC-5, tjrob137 wrote: |

>> | On 7/14/18 11:39 AM, Ed Lake wrote: |

>>> | [about his suggested experiment] The clocks that were spun are then compared to the control clock that was not spun. The clocks that were spun will show that they ticked slower while moving. |

>> | No, they won't. You keep getting this wrong. They will have ticked fewer times, but this says NOTHING AT ALL about their tick rate. Their tick rate is COMPLETELY UNAFFECTED. |

> |
So, if a moving clock ticks fewer times than a stationary clock during a given period of time, their tick rate is "unaffected"? |

Yes.

> | The only way I can make sense of that is [...] |

YOUR GUESSES ARE WRONG.

The centrifuge clock travels a helical path through spacetime, while the lab clock travels a straight-line (inertial) path through spacetime. These paths are manifestly different, and they differ in elapsed proper time by 0.93 ns for this experiment.

This experiment does NOT measure gravitational "time dilation" [#], it is an implementation of the twin paradox and measures the difference in elapsed proper times over different paths through spacetime.

On 7/15/18 3:27 PM, Ed Lake wrote:

> | PRETENDING that you are stationary doesn't mean you are stationary. |

What we do is not "pretending to be stationary", but rather we are DEFINING what "stationary" means.

You continually want to introduce some "absolute" or "God's eye" frame that you think is "truly stationary". There _IS_ no such thing. All one can do is specify "I'll apply the word 'stationary' to this frame."

> | In the centrifuge experiment it isn't as much about how fast objects move, it is about GRAVITY. |

Nope, if the lab clock is at the same altitude as the centrifuge clock.

SPINNING IS NOT GRAVITATION.

> | [... more nonsense completely irrelevant to this experiment] |

Tom Roberts

On Friday, July 13, 2018 at 1:22:40 PM UTC-7, tjrob137 wrote:

> |
To compute gamma, no normal calculator has sufficient precision, so I switch to Python's decimal module with 28 digit precision: c = Decimal(299792458.0) gamma = Decimal(1.0)/Decimal.sqrt(Decimal(1.0)-v*v/c/c) t = 22*3600 delta_t = Decimal(t) * (gamma-Decimal(1.0)) print(gamma,delta_t) 1.000000000000011771837593048 9.32329537369401600E-10 |

Unless, of course, it's the DM42 calculator from Swiss Micros: https://www.swissmicros.com/dm42.php

It's an HP-42s clone with precision increased to 34 decimal digits (IEEE 754-2008 quadruple precision floating-point). I simply cannot recommend it highly enough, it's VERY well-made too, reproducing the famous HP key click feel very well. It's better than any calculator offered by HP today, plus one can use the excellent HP-42s manual with this which is an important thing as HP manuals are in a class of their own.

In the above calculation the DM42 easily shows an increased precision:

On Friday, July 13, 2018 at 3:22:40 PM UTC-5, tjrob137 wrote:

> | On 7/13/18 12:10 PM, Ed Lake wrote: |

> > | The human centrifuge at NASA's Ames Research Center in Mountain View, CA, can generate 20Gs of gravity for up to 22 hours while spinning a payload of 1,200 pounds or less. https://www.nasa.gov/ames/research/space-biosciences/20-g-centrifuge |

> |
It's not "20Gs of gravity", it is an acceleration of 20 g. Spinning is NOT gravity (DUH!). Moreover, for computing the "time dilation" of a clock the acceleration simply does not matter. All that matters is the velocity relative to the lab. That is, since everything is supported against earth's gravity and located at the same altitude [#], we can neglect gravity and analyze in an inertial frame at rest in the lab. [#] We will place the lab clock at the same altitude as the centrifuge clock. From the above link, the centrifuge has a radius of 29 ft and can spin at 50 RPM. 29 ft is 8.8 meters, and 50 RPM has a period of 60/50 seconds; the velocity relative to the lab frame is: = 2 * 3.14 * 8.8 / 1.2 = 46 meters/second |

For this problem in particular, switching to Python's decimal module is a bit of overkill. Since v << c, we can just use the first terms of a Taylor series expansion.

using my old TI-89
v = 46
c = 299792458
gamma = 1/sqrt(1 - v^2/c^2) ˜ 1/(1 - 0.5 * v^2/c^2) ˜ 1 + 0.5 * v^2/c^2

= 1 + 1.1771837593048e-14 = 1.000000000000011771837593048

1.1771837593048e-14 * 22 * 3600 = 9.32e-10 seconds

> |
v = Decimal(46.0) c = Decimal(299792458.0) gamma = Decimal(1.0)/Decimal.sqrt(Decimal(1.0)-v*v/c/c) t = 22*3600 delta_t = Decimal(t) * (gamma-Decimal(1.0)) print(gamma,delta_t) 1.000000000000011771837593048 9.32329537369401600E-10 |

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Calculating the Doppler shift of a be... Show trimmed content

Tom Roberts wrote:

> | [gravitational time dilation] SPINNING IS NOT GRAVITATION. |

True. However, as there is acceleration involved in spinning, does the Einstein equivalence principle not imply the same observations (in addition to those explained by relative motion) as if the system in question would not be spinning, but were in a gravitational field?

—Albert Einstein, “On the Influence of Gravitation on the Propagation of Light” (1911) (official translation into English)

Cited in: https://en.wikipedia.org/wiki/Equivalence_principle#Development_of_gravitation_theory>

-- PointedEars

Twitter: @PointedEars2 Please do not cc me. / Bitte keine Kopien per E-Mail.

On Monday, July 16, 2018 at 3:34:20 AM UTC-5, Thomas 'PointedEars' Lahn wrote:

> | Tom Roberts wrote: |

> > | [gravitational time dilation] SPINNING IS NOT GRAVITATION. |

> |
True. However, as there is acceleration involved in spinning, does the Einstein equivalence principle not imply the same observations (in addition to those explained by relative motion) as if the system in question would not be spinning, but were in a gravitational field? |

That, of course, was the point that I was trying to make in my post of July 15, 2018 at 11:32:58 PM UTC-5 on this thread.

In Roberts' post of July 13, 2018 at 3:22:40 PM UTC-5, the lab observer calculates the time dilation as being strictly due to the speed of the clock relative to the lab.

In my post, the moving observer on the circumference of the centrifuge calculates the frequency shift of a light beam between himself and the center as being due to the difference in potential between himself and the center due to the centrifugal (pseudo)force.

> > |
An atomic clock that is one foot higher than an
identical atomic clock will tick faster.
They can measure the difference.
The issue is how slow will an atomic clock experiencing 20Gs tick versus a clock experiencing 1G? Ed |

> |
You are harping on this particular acceleration for some reason? What is your point? This is a typical kook tactic to propose a useless experiment when other equivalent experiments have proven them wrong. So really, why this value: 20G? in a centrifuge? Why are the other experiments not good enough for your? What meat this experiment special? What do you hope to find? Ed |

I used 20Gs because that that is the maximum that NASA's Ames Research Center centrifuge can generate. https://www.nasa.gov/ames/research/space-biosciences/20-g-centrifuge

What I would expect the centrifuge experiment to find is that time for the clocks on the centrifuge runs significantly slower than time for the clock in the control room. The clocks on the centrifuge would tick s... Show trimmed content

On 7/14/18 12:33 PM, Ed Lake wrote:

> | On Friday, July 13, 2018 at 10:34:07 PM UTC-5, tjrob137 wrote: |

>> | On 7/13/18 3:58 PM, Ed Lake wrote: |

>>> | Nope. Gravitational time dilation slows down time and so does velocity time dilation. Einstein's elevator thought experiment says that acceleration has the same effect on time as gravity. |

>> |
All three sentences are WRONG. Time does NOT "slow down", but COMPARISONS OF CLOCK TICK RATES via signals can show that the SIGNALS can slow down (they can also speed up). (Ditto for comparisons of elapsed proper times over different paths.) |

> |
What signals? You always argue about fantasy "signals" that you make up! The experiment involves NO signals. You compare the 5 clocks before the test, you spin 4 of the clocks for some period, then you compare the clocks again. No fantasy signals. |

You are supposed to read what I write before attempting to respond. Earlier in that post I said:

(In this case, after the comma I also gave two examples of quantities that do slow down (or speed up) or differ.)

Given that you do not understand general rhetorical patterns [#], it's no surprise that you get so many things wrong. YOU REALLY NEED TO LEARN HOW TO READ.

[#] After disagreeing with an opponent's incorrect claim, giving related examples that are correct.

>> | [H&K's clocks] specified by their manufacturer to operate only under accelerations less than 2 g. After all, they use an atomic beam in freefall, and at 20 g it will not remain in the waveguides used to measure its frequency; the mechanical structure might not remain stable. |

> |
They are specified to be used at less than 2Gs because above 2Gs you will get measurable gravitational effects that may cause you to reset your clock if you have no interest in those effects. |

Nope. YOU DO NOT UNDERSTAND THIS -- gravitational "time dilation" is NOT related to the acceleration of the clocks, it is related to the difference in their gravitational potentials; it is a comparison of two clocks located at different gravitational potentials, and does not affect a single clock. As I keep saying: CLOCKS ALWAYS TICK AT THEIR USUAL RATE.

There _ARE_ no "gravitational effects" that affect a single clock [%]. Such clocks are specified to operate at less than 2 g because larger accelerations could damage them.

On 7/15/18 11:32 PM, Prokaryotic Caspase Homolog wrote:

> | On Friday, July 13, 2018 at 3:22:40 PM UTC-5, tjrob137 wrote: |

>> | To compute gamma, no normal calculator has sufficient precision, so I switch to Python's decimal module with 28 digit precision: [...] |

> |
For this problem in particular, switching to Python's decimal module is a bit of overkill. Since v << c, we can just use the first terms of a Taylor series expansion. |

Sure. But I doubt very meany people around here understand that, so I chose the simpler approach of using a "calculator" with sufficient significant digits.

Tom Roberts

On 7/16/18 3:34 AM, Thomas 'PointedEars' Lahn wrote:

> | Tom Roberts wrote: |

>> | [gravitational time dilation] SPINNING IS NOT GRAVITATION. |

> |
True. However, as there is acceleration involved in spinning, does the Einstein equivalence principle not imply the same observations (in addition to those explained by relative motion) as if the system in question would not be spinning, but were in a gravitational field? |

Yes, within limits. Here we meet those limits and can consider the rotating centrifuge to be "generating" an equivalent gravitational field in its rotating frame. Note that in these coordinates the centrifuge clock is not moving; let's place the lab clock at the center of rotation, so it is also not moving relative to these coordinates (and is also not moving relative to the lab).

Here are three calculations of the difference in elapsed proper time between the centrifuge and lab clocks:

1. Centrifuge clock's "time dilation" relative to the lab frame: sqrt(1-v^2/c^2), with v the clock's speed relative to the lab, measured in the lab. Integrate this over 22 hours and one gets 0.93 ns over 22 hours.

2. Centrifuge clock's "equivalent gravitational time ...

Tom Roberts

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