My lecturer says "Special relativity is absolutely wrong"

[Seanra]

Hi guys

In an assignment I wrote for university I was penalised for claiming that FTL neutrinos would violate special relativity.

Below is the relevant part of my assignment and the response from my lecturer. Could somebody please explain what he could mean by that because as far as I can tell, FTL particles violate special relativity and special relativity is not "absolutely wrong".

https://imgur.com/bXt3O6K

 

[DrSuage]

Faster than light neutrinos don't exist - the experiment that purported to find them in 2011 turned out to have electrical flaws that lead to misleading data.
Of course were they to exist they would violate SR.

 

[DrSuage]

His little schpiel about General Relativity allowing faster than light travel is absolute hokum.
Special Relativity is not wrong in the way that Newtonian mechanics is not wrong. They are just approximate theories - effective only within their domain of application.

 

[russ_watters]

What class/level is that for?

 

[Battlemage!]

If I'm not mistaken, general relativiy posits that curved spacetime must reduce to the physics of special relativity for small free falling areas. Which would suggest in a free falling frame (a local inertial frame) the speed of light is still the max speed locally.

 

[Orodruin]

Locally, the speed of light is the upper limit, GR and SR agrees on this. On a global level, you would have to (very carefully) define what you mean by "travelling faster than light" if you are going to make such blanket statements.

 

[Seanra]

Faster than light neutrinos don't exist - the experiment that purported to find them in 2011 turned out to have electrical flaws that lead to misleading data.
Of course were they to exist they would violate SR.

Yup, the contention of my assignment was that scientific anomalies such as the "discovery" of FTL neutrinos are usually due to experimental error.

His little schpiel about General Relativity allowing faster than light travel is absolute hokum.
Special Relativity is not wrong in the way that Newtonian mechanics is not wrong. They are just approximate theories - effective only within their domain of application.

Yup exactly what I thought. Alas I'm still going to lose marks sigh...

What class/level is that for?

A philosophy of physics class at one of the top universities in Australia. Kind of disappointing. (btw guys please don't go trying to message my lecturer saying he is wrong, I get the feeling that would screw me over pretty bad).

 

[Seanra]

Okay guy's i really need to know if I'm missing something here or is my lecturer brainwashing my entire class into thinking special relativity is wrong and completely superseded by general relativity.

Here is a discussion one of the students in my class had with the lecturer:

https://imgur.com/kysV8bn

 

[Seanra]

Locally, the speed of light is the upper limit, GR and SR agrees on this. On a global level, you would have to (very carefully) define what you mean by "travelling faster than light" if you are going to make such blanket statements.

Putting aside what my lecturer said for a moment, I have a question: Due to the expansion of the universe, galaxies the distance between distance galaxies grows extremely quickly over time. Can we say in any sense that these galaxies are traveling faster than the speed of light?

 

[jbriggs444]

Putting aside what my lecturer said for a moment, I have a question: Due to the expansion of the universe, galaxies the distance between distance galaxies grows extremely quickly over time. Can we say in any sense that these galaxies are traveling faster than the speed of light?

No. It would be better to stick with the statement that their separation grows quickly over time.

Edit: One could pick a coordinate system in which one galaxy is at rest and the other galaxy has a velocity faster than the speed of light. But that "velocity" is as much an artifact of the choice of the coordinate system as anything physical. Pick another coordinate system and you get another "velocity". One ought not give such "velocities" the courtesy of calling them by that name.

 

[jbriggs444]

On the notion of SR being "absolutely wrong", Isaac Asimov had something to say...
http://hermiene.net/essays-trans/relativity_of_wrong.html

 

[russ_watters]

A philosophy of physics class...

Taught by a physicist or philosopher?Just the title makes my skin crawl.

 

[Seanra]

Taught by a physicist or philosopher?

Just the title makes my skin crawl.

I think you can guess the answer to that...

On the notion of SR being "absolutely wrong", Isaac Asimov had something to say...
http://hermiene.net/essays-trans/relativity_of_wrong.html

Ahaha that's a good read.

Guys are there ANY circumstances under which special relativity is superseded by general relativity? Is there at least an inkling of truth to what he is saying?

 

[ChrisVer]

Why would FTL particles violate SR?
Something that could potentially violate SR is for massive particles to travel at the speed of light... the region of traveling slower and faster than the speed of light are nicely defined in SR.

 

[jtbell]

Guys are there ANY circumstances under which special relativity is superseded by general relativity?

General relativity applies when there is gravity. Special relativity is a good approximation when gravitational effects are "small enough" that we can ignore them for the purposes at hand.

 

[atyy]

Hi guys

In an assignment I wrote for university I was penalised for claiming that FTL neutrinos would violate special relativity.

Below is the relevant part of my assignment and the response from my lecturer. Could somebody please explain what he could mean by that because as far as I can tell, FTL particles violate special relativity and special relativity is not "absolutely wrong".

https://imgur.com/bXt3O6K

Your lecturer is wrong, because special relativity is a great approximation to general relativity in some domain, and the report of superluminal neutrinos was in the domain where special relativity is expected to hold.

 

[atyy]

Putting aside what my lecturer said for a moment, I have a question: Due to the expansion of the universe, galaxies the distance between distance galaxies grows extremely quickly over time. Can we say in any sense that these galaxies are traveling faster than the speed of light?

In a strict sense, general relativity forbids the comparison of velocities of distant objects. Only special relativity permits it.

There is a sense in which the galaxies can be said to be traveling faster than the speed of light, but it is not in the same sense in which the neutrinos were said to be traveling faster than light.

See post #10 by jbriggs444 above.

 

[Seanra]

In a strict sense, general relativity forbids the comparison of velocities of distant objects. Only special relativity permits it.

There is a sense in which the galaxies can be said to be traveling faster than the speed of light, but it is not in the same sense in which the neutrinos were said to be traveling faster than light.

See post #10 by jbriggs444 above.

Thanks for that explanation. So I guess the question is, if I want to go about trying to convince him that he is wrong (an extremely difficult thing to accomplish when he has based entire lectures on SR being wrong) how should I go about it and what are some of the best sources I can use to back up my claims?

 

[Orodruin]

Well, technically, he is not "wrong", just as SR is not "wrong". The concept of "wrong" is not very useful when dealing with scientific models and it is much more relevant to discuss whether a model is "useful" or not. Newtonian mechanics might be considered "wrong" as it does not describe what we can observe at large velocities or small distances. However, this does not invalidate Newtonian mechanics, it just restricts its domain of applicability. It still works perfectly fine for most every-day applications.

In the same sense, SR is not "wrong" it is just not applicable to some situations when space-time curvature becomes significant. If your lecturer wants to take his argument to the extreme - GR is also "wrong", although its domain of applicability is larger than that of SR.

 

[russ_watters]

So I guess the question is, if I want to go about trying to convince him that he is wrong (an extremely difficult thing to accomplish when he has based entire lectures on SR being wrong) how should I go about it and what are some of the best sources I can use to back up my claims?

I would talk to a physics professor at your university about it. You are unlikely to win an argument like this on your own, regardless of what sources you provide.

 

[russ_watters]

Well, technically, he is not "wrong", just as SR is not "wrong". The concept of "wrong" is not very useful when dealing with scientific models and it is much more relevant to discuss whether a model is "useful" or not. Newtonian mechanics might be considered "wrong" as it does not describe what we can observe at large velocities or small distances.

So...[to the OP] in the context of the Asimov essay, don't argue with the prof that he's wrong, argue that you aren't wrong. If you don't make them mutually exclusive it may go over better......even if I disagree with Orodruin based on the professor's wording choice: "absolutely wrong". About the only time one can be totally right or totally wrong on something like this is to make a binary/absolute claim!

 

[atyy]

Thanks for that explanation. So I guess the question is, if I want to go about trying to convince him that he is wrong (an extremely difficult thing to accomplish when he has based entire lectures on SR being wrong) how should I go about it and what are some of the best sources I can use to back up my claims?

A major counterargument are the neutrinos from supernova SN1987A:
http://resonaances.blogspot.sg/2011/09/phantom-of-opera.html
https://profmattstrassler.com/artic...-than-light/opera-comparing-the-two-versions/

Although the counterargument does use neutrinos that have traveled large distances, at each point their velocity is well-defined in the same sense that special relativity holds locally, even in general relativity, so it is a valid argument where the concept of velocity is consistent throughout (as opposed to the "superluminal" expansion of the universe, which refers to a different type of "velocity").

A further source supporting your argument is http://arxiv.org/abs/1109.4897 which says the the OPERA result would contradict Lorentz invariance. In the context of GR, one would understand the term to mean local Lorentz invariance, ie. that special relativity holds locally.

For a source that the "superluminal" expansion of the universe is not a correct counterexample, one can cite https://preposterousuniverse.com/wp-content/uploads/grnotes-three.pdf "In cosmology, for example, the light from distant galaxies is redshifted with respect to the frequencies we would observe from a nearby stationary source. Since this phenomenon bears such a close resemblance to the conventional Doppler effect due to relative motion, it is very tempting to say that the galaxies are “receding away from us” at a speed defined by their redshift. At a rigorous level this is nonsense, what Wittgenstein would call a “grammatical mistake” — the galaxies are not receding, since the notion of their velocity with respect to us is not well-defined." [bolding by me]

 

[Seanra]

Well, technically, he is not "wrong", just as SR is not "wrong". The concept of "wrong" is not very useful when dealing with scientific models and it is much more relevant to discuss whether a model is "useful" or not. Newtonian mechanics might be considered "wrong" as it does not describe what we can observe at large velocities or small distances. However, this does not invalidate Newtonian mechanics, it just restricts its domain of applicability. It still works perfectly fine for most every-day applications.

In the same sense, SR is not "wrong" it is just not applicable to some situations when space-time curvature becomes significant. If your lecturer wants to take his argument to the extreme - GR is also "wrong", although its domain of applicability is larger than that of SR.

Hey just to make sure we're all on the same page, have you seen the screencap I posted in my first message that shows what I said and what my lecturer said? Is SR relevant to the discussion of the now debunked FTL neutrinos that were "discovered" by OPERA?

 

[Seanra]

A major counterargument are the neutrinos from supernova SN1987A:
http://resonaances.blogspot.sg/2011/09/phantom-of-opera.html
https://profmattstrassler.com/artic...-than-light/opera-comparing-the-two-versions/

Although the counterargument does use neutrinos that have traveled large distances, at each point their velocity is well-defined in the same sense that special relativity holds locally, even in general relativity, so it is a valid argument where the concept of velocity is consistent throughout (as opposed to the "superluminal" expansion of the universe, which refers to a different type of "velocity").

A further source supporting your argument is http://arxiv.org/abs/1109.4897 which says the the OPERA result would contradict Lorentz invariance. In the context of GR, one would understand the term to mean local Lorentz invariance, ie. that special relativity holds locally.

For a source that the "superluminal" expansion of the universe is not a correct counterexample, one can cite https://preposterousuniverse.com/wp-content/uploads/grnotes-three.pdf "In cosmology, for example, the light from distant galaxies is redshifted with respect to the frequencies we would observe from a nearby stationary source. Since this phenomenon bears such a close resemblance to the conventional Doppler effect due to relative motion, it is very tempting to say that the galaxies are “receding away from us” at a speed defined by their redshift. At a rigorous level this is nonsense, what Wittgenstein would call a “grammatical mistake” — the galaxies are not receding, since the notion of their velocity with respect to us is not well-defined." [bolding by me]

Thankyou so much for this Atyy, I'm going to head to bed now but I'll read over this in the morning and get back to you and everybody else :)

Thanks again everybody, I really appreciate your input!

 

[PAllen]

In a strict sense, general relativity forbids the comparison of velocities of distant objects. Only special relativity permits it.

There is a sense in which the galaxies can be said to be traveling faster than the speed of light, but it is not in the same sense in which the neutrinos were said to be traveling faster than light.

See post #10 by jbriggs444 above.

Right, and in that sense, SR also allows FTL motion. Using Milne coordinates (cosmological analog coordinates in flat spacetime) in SR, test bodies may have arbitrarily large growth rate of separation between them. Celerity (another type of velocity in SR) may also be unbounded. There is close analogy between cosmological recession rates and SR celerity.

 

[ProfuselyQuarky]

Kind of off topic and I'm not so sure about the university level, but sometimes when I dispute with a teacher about something (i.e. supposed error in my work) I will email them with my explanation (w/ sources) and I get back the credit and points that I would have initially lost. Especially when it has to do with theory or even writing style. Could you try that? (Or do I just happen to have nice instructors?)

 

[PAllen]

Why would FTL particles violate SR?
Something that could potentially violate SR is for massive particles to travel at the speed of light... the region of traveling slower and faster than the speed of light are nicely defined in SR.

Well, note that massive particles traveling FTL clearly violates SR. What is allowed (if one does not include causality assumptions in your definition of SR) is imaginary mass particles traveling FTL. Thus, kinematic SR states emphatically: massive particles travel < c, massless particles travel at c, and imaginary mass particles travel >c, always. If imaginary mass particles can interact with massive matter, then messages can be sent to your past.

 

[gjonesy]

Hmmm...a simple way to end that debate is repeating the results of that experiment. If its not repeatable and the findings verified and peer reviewed well then that assumption of FTL can not hold true ...correct?

 

[Orodruin]

Hmmm...a simple way to end that debate is repeating the results of that experiment. If its not repeatable and the findings verified and peer reviewed well then that assumption of FTL can not hold true ...correct?

There is nothing "simple" about repeating the OPERA experiment. It is a big collaboration and has taken several years of planning and performance. There are other neutrino experiments who have done similar measurements with negative results and the OPERA experiment itself has retracted the claim, I do not see a point in continuing to beat that particular dead horse.

 

[gjonesy]

I do not see a point in continuing to beat that particular dead horse.

My point exactly,... I should have specified that his lecturer should confirm his belief that neutrinos were FTL via a repeatable experiment...lol That was my attempt at humor and sarcasm.