Undergrad Simplified explanation of SR for relativity-denier

[Meir Achuz]

He may be right. Since the earth is flat, that could change everything.

 

[Herman Trivilino]

True, but I don't think they are that portable. Maybe an RV?

Huhh? You can put an atomic clock on an RV and drive it at walking or jogging speeds. You don't have to be walking or jogging to move at a walking or jogging speed.

 

[ersmith]

Our most sensitive clocks can detect relativistic effects at walking/jogging speeds.

I'm aware of Chou et al observing time dilation at 10 m/s, which is Olympic sprinter speed, but hadn't heard of further improvements. It wouldn't surprise me though, Chou's work was a few years ago.

 

[JLowe]

There's a reason we just ban them here. Arguing with them is like shooting zombie fish in a barrel. You can't miss, but you can't stop 'em either.

To be honest, arguing with them feels a bit like being a bully. Like you're picking on someone smaller than you.

 

[Sagittarius A-Star]

I'm aware of Chou et al observing time dilation at 10 m/s, which is Olympic sprinter speed, but hadn't heard of further improvements. It wouldn't surprise me though, Chou's work was a few years ago.

I found this:

Resolving the gravitational redshift across a millimetre-scale atomic sample
...
Nature volume 602, pages420–424 (2022)
...
Abstract
Einstein’s theory of general relativity states that clocks at different gravitational potentials tick at different rates relative to lab coordinates—an effect known as the gravitational redshift¹. As fundamental probes of space and time, atomic clocks have long served to test this prediction at distance scales from 30 centimetres to thousands of kilometres^2,3,4. Ultimately, clocks will enable the study of the union of general relativity and quantum mechanics once they become sensitive to the finite wavefunction of quantum objects oscillating in curved space-time. Towards this regime, we measure a linear frequency gradient consistent with the gravitational redshift within a single millimetre-scale sample of ultracold strontium. Our result is enabled by improving the fractional frequency measurement uncertainty by more than a factor of 10, now reaching 7.6 × 10⁻²¹. This heralds a new regime of clock operation necessitating intra-sample corrections for gravitational perturbations.

Source:
https://www.nature.com/articles/s41586-021-04349-7

A free version:
https://arxiv.org/abs/2109.12238

 

[Meir Achuz]

The gravitational red shift can be derived in special relativity as an acceleration red shift for an orbiting satellite.

 

[vanhees71]

Gravitation is described by GR and not in SR. I also don't know, what "an acceleration red shift" should be.

 

[PeterDonis]

Gravitation is described by GR and not in SR. I also don't know, what "an acceleration red shift" should be.

He's referring to the redshift that occurs when sending light from the bottom to the top of a rocket accelerating in flat spacetime (which is described by the Rindler congruence of worldlines). Calling it "gravitational" redshift is fairly common in the literature, based on the equivalence principle. But of course this use of "gravitational" does not imply spacetime curvature, which is what GR is necessary to describe.

 

[Nugatory]

He's referring to the redshift that occurs when sending light from the bottom to the top of a rocket accelerating in flat spacetime (which is described by the Rindler congruence of worldlines). Calling it "gravitational" redshift is fairly common in the literature, based on the equivalence principle. But of course this use of "gravitational" does not imply spacetime curvature, which is what GR is necessary to describe.

If people were going to be precise in their use of natural language, we’d be saying something like “gravity-equivalent redshift” or “equivalence-principle redshift” instead of “gravitational redshift”….. but of course natural language is not and never has been about being precise.

 

[FactChecker]

As an every day (but theoretical) example of SR, I like how SR explains the relationship between a moving electric charge and magnetic attraction. It makes magnetic attraction much less "magical". (see this)

 

[Meir Achuz]

The gravitational red shift can be derived in special relativity as an acceleration red shift for an orbiting satellite.

I am afraid that, partly due my wording of it, this post has led to ...
There is an 'acceleration red shift' in special relativity, that can be derived without using Rindler coordinates.
I mistakenly thought that was well-known. I have only seen it derived for acceleration parallel to the velocity.
For instance, the watches of passengers at the front end of an accelerating rocketship will show a different time than those at the rear end. I am not sure, but I think that the derivation would not work for acceleration perpendicular to the velocity, as in an orbiting satellite. That means that this red shift would not apply to a GPS.

 

[PeterDonis]

I think that the derivation would not work for acceleration perpendicular to the velocity, as in an orbiting satellite.

An orbiting satellite has no proper acceleration. It is in free fall. It has coordinate acceleration in a frame in which the Earth is at rest, but coordinate acceleration is not what leads to the red shift. Proper acceleration is.

As for proper acceleration perpendicular to the velocity, you have to be very careful to specify which observers are going to be testing for a red shift. It is certainly possible to find a pair of such observers that will see a redshift/blueshift when they exchange light signals.

 

[ebg]

There are no truth in science, just answers agreed upon to be the best solution for the moment...didn't they imprisoned Galileo for having ideas contrary to Aristotle's? If SR is an absolute....then there is nothing to fear from dissent

 

[Ibix]

then there is nothing to fear from dissent

We're not really talking about dissent here, though. We're talking about people who would fail an introductory course in relativity and regard that as a badge of honour. That's not dissent, it's just the Dunning-Kruger effect.

 

[Dale]

there is nothing to fear from dissent

There is actually a large body of recent experimental work seeking more and more subtle evidence of Lorentz violations. Such signals would be very informative for physics beyond the standard model. So not only is there no actual fear of dissent there is active seeking of it, and great prestige and financial rewards for achieving it.

Don’t mistake the quick dismissal of obviously ignorant speculation as a general opposition to dissent.

 

[Drakkith]

didn't they imprisoned Galileo for having ideas contrary to Aristotle's?

Yes, with 'they' being the Catholic Church. Having contrary ideas is welcome in science as long as those ideas are logical, self consistent, and testable. Unfortunately many 'contrarians' don't understand this and loudly decry science as dogmatic and intolerant, when in reality it's like going to your math teacher and expecting them to take you seriously when you hand in a 5-page report that says 1+1 = 11.

 

[Sagittarius A-Star]

when you hand in a 5-page report that says 1+1 = 11.

The correct notation would be Ⅰ+Ⅰ = Ⅱ.

Source:
https://symbl.cc/en/collections/roman-numerals/

 

[ebg]

Yes, with 'they' being the Catholic Church. Having contrary ideas is welcome in science as long as those ideas are logical, self consistent, and testable. Unfortunately many 'contrarians' don't understand this and loudly decry science as dogmatic and intolerant, when in reality it's like going to your math teacher and expecting them to take you seriously when you hand in a 5-page report that says 1+1 = 11.

on the other hand....1+1=2 is an axiom....it can't be proven, but is accepted as being true because the probability of the outcome it being 2 is quite high. What is the possibility (not probability) of the sum of 1+1 = 11? QED is not a proof.

 

[phinds]

on the other hand....1+1=2 is an axiom....it can't be proven

Not true. There have been a number of proofs, the earliest of which that I am aware of is a VERY long, involved one by Bertrand Russell and Alfred North Whitehead over 100 years ago.

 

[Ibix]

on the other hand....1+1=2 is an axiom....it can't be proven

Bertrand Russell would like a word...

What is the possibility (not probability) of the sum of 1+1 = 11

Easy - try to find a set of self consistent axioms that include or imply that. If you succeed you have your answer.

 

[Nugatory]

on the other hand....1+1=2 is an axiom....it can't be proven, but is accepted as being true because the probability of the outcome it being 2 is quite high. What is the possibility (not probability) of the sum of 1+1 = 11? QED is not a proof.

It is a bit of a digression here, but 1+1=2 is a theorem that can be proven from axioms of arithmetic.

This is a different situation than claims made by empirical science, which are based on experimental evidence and observations about how the world works, and are evaluated based on the accuracy and generality of their predictions. A challenge to such a theory will only be taken seriously if we either produce empirical evidence showing that the predictions are incorrect, or we advance an alternative theory that produces, to the limits of experimental accuracy, the same predictions as the existing theory and also produces correct predictions outside of the range of validity of the existing theory.

 

[Dale]

1+1=2 is an axiom....it can't be proven, but is accepted as being true because the probability of the outcome it being 2 is quite high

That is completely ridiculous. It has nothing whatsoever to do with probability.

On this forum, all posts need to be consistent with the professional scientific literature.

 

[PeroK]

This is a different situation than claims made by empirical science, which are based on experimental evidence and observations about how the world works, and are evaluated based on the accuracy and generality of their predictions. A challenge to such a theory will only be taken seriously if we either produce empirical evidence showing that the predictions are incorrect, or we advance an alternative theory that produces, to the limits of experimental accuracy, the same predictions as the existing theory and also produces correct predictions outside of the range of validity of the existing theory.

The mathematics that is used to underpin physical theories is, in a way, tested along with the theories themselves. Basic arithmetic, wherever it comes from, is tested alongside the physical postulates. The same goes for vectors, calculus, differential geometry etc. It doesn't really matter whether you can mathematically justify the real numbers. They are, in a way, physically justified by the success of the physical theories based on them!

 

[nasu]

it's like going to your math teacher and expecting them to take you seriously when you hand in a 5-page report that says 1+1 = 11.

Whereas it should be 1+1=10.

 

[PeterDonis]

Whereas it should be 1+1=10.

If you only have two fingers to count with, perhaps...

 

[FactChecker]

If you only have two fingers to count with, perhaps...

Do you suppose that is the reason that we use base 10? Because we can count on 10 fingers?

 

[PeterDonis]

Do you suppose that is the reason that we use base 10? Because we can count on 10 fingers?

AFAIK it's one hypothesis.

 

[Nugatory]

Whereas it should be 1+1=10.

There are 10 kinds of people in the world. Those who know ternary, those who don't know ternary, and those who were expecting a joke about binary.

 

[nasu]

AFAIK it's one hypothesis.

This means that the romans did not have 10 fingers?

 

[phinds]

This means that the romans did not have 10 fingers?

Oh, they had 10 fingers, but they were VERY inventive with obscene gestures requiring various combinations fingers to produce many variations of insults.