Was Richard Feynman's explanation of the twin paradox wrong?

[gen x]

Here Tim Maudlin explain that acceleration is not reason why one twin become younger, and that Feynman explained that wrongly?
Is this correct and can you explain what he want to say?

 

[.Scott]

Feynman said that the reason that one twin ages differently was that one accelerated and the other didn't.
So long as you are comparing something that has accelerated with something that has not accelerated at all, that logic will tell you which one aged more.

Tim is picking on Feynman's comment because even though that acceleration distinction tells you why the twins aged differently in this case, it doesn't pull in the equations that you would need to work through to calculate the aging of each child.
And those equations are about more than just the acceleration.

 

[gen x]

Feynman said that the reason that one twin ages differently was that one accelerated and the other didn't.
So long as you are comparing something that has accelerated with something that has not accelerated at all, that logic will tell you which one aged more.

Tim is picking on Feynman's comment because even though that acceleration distinction tells you why the twins aged differently in this case, it doesn't pull in the equations that you would need to work through to calculate the aging of each child.
And those equations are about more than just the acceleration.

I didnt understand well, so where was Feynman wrong?

 

[martinbn]

Why do you watch you tube videos instead of studying physics textbooks?

 

[PeroK]

I didnt understand well, so where was Feynman wrong?

There's no single, correct way to explain the twin paradox. People on YouTube who prefer a certain explanation like to say that everyone else is wrong.

It's ultimately about click bait.

 

[Paul Colby]

I didnt understand well, so where was Feynman wrong?

The two twins follow two different paths. One twins path proper length is shorter. As setup, the shorter path twin must accelerate to get on this shorter length path. The shorter path length isn’t shorter because it takes acceleration for the twin to change to it. It’s shorter because it’s shorter.

 

[A.T.]

Here Tim Maudlin explain that acceleration is not reason why one twin become younger

Depends on what one means by "reason why".

Try this analogy:

The rate at which an odometer reading increases is not directly affected by the steering, just by speed. But the steering on the way between two points affects the total distance accumulated by the odometer, and knowing the complete steering profile allows you to compute it.

So is "steering" the "reason why" the odometer accumulated more distance on the way between two points?

Correspondence:
odometer distance : proper time interval
steering : proper acceleration
the relationship is also inverted: no proper acceleration -> more proper time

 

[PeroK]

The idea that Richard Feynman didn't understand the basics of relativity as well as anyone else who ever lived is cretinous.

 

[Roberto Pavani]

I'd put it this way: the question "where was Feynman wrong?" isn't well-defined, because there's no single "the" explanation of the twin paradox to be right or wrong about. Feynman gives the qualitative marker (acceleration breaks the symmetry); Maudlin insists on the quantity (proper time along the worldline). They answer different questions. As @PeroK says, framing it as "someone was wrong" is the clickbait part.

 

[.Scott]

Why do you watch you tube videos instead of studying physics textbooks?

Clearly, there are many possible reasons.
Perhaps you would like to suggest a particular text that does a good job covering this topic and comes in under $20 or is online and free.

 

[PeterDonis]

Insights Thread 'When Discussing the Twin Paradox: Read This First'

Jan 2, 2023

This article is intended for anyone who wants to start a thread here at PhysicsForums on the twin paradox. There are already many, many threads here on this topic, and they tend to cover the same ground over and over again, so it seems useful to put a description of that ground into an article that everyone can read before starting yet another thread. If you are in that category, and what is here answers your question, great! But even if it doesn’t, hopefully, this article will help you to frame whatever questions you still have after reading it, in a way that will help you to get...

• PeterDonis
• Paradox Twin paradox
• Replies: 2
• Forum: Special and General Relativity

• 
• 

 

[PeterDonis]

Perhaps you would like to suggest a particular text that does a good job covering this topic and comes in under $20 or is online and free.

Taylor & Wheeler:

https://phys.libretexts.org/Bookshelves/Relativity/Spacetime_Physics_(Taylor_and_Wheeler)

 

[.Scott]

I didnt understand well, so where was Feynman wrong?

There is no reason to believe that Feynman went wrong anywhere. The video does not provide a specific Feynman quote - so there is no context what-so-ever.
And in this case, context is paramount. The criticism, at its core, is that the statement attributed to Feynman is incomplete. So, if we had a specific citation we could look at the context. In context, we might discover that Feynman continued with a discussion on exactly the topic that Tim Maudlin is addressing. Or we might discover that the situation did not merit a more detailed description given the setting and the purpose of the statement.

Also, this comment did not originate with Feynman. Five years before Feynman was born, Max von Laue addressed this same topic and highlighted the changing reference frame (ie acceleration) as the key discriminant.
But let's face it, between "Feynman's big mistake" and "von Laue's big mistake" are thousands of views.
As @PeroK said, this ultimately boils down to clickbait.

 

[Histspec]

Also, this comment did not originate with Feynman. Five years before Feynman was born, Max von Laue addressed this same topic and highlighted the changing reference frame (ie acceleration) as the key discriminant.

Pretty much everything related to the twin paradox has already been discussed and solved between 1910 and 1921.
History of the twin paradox

 

[FactChecker]

Although Feynman's statement might be incomplete, IMO it addresses the main misconception that leads people to think there is a paradox, namely that the twins perspectives are identical. They are not identical. One accelerates and is not stationary in a single IRF the entire time.

 

[Nugatory]

Five years before Feynman was born, Max von Laue addressed this same topic and highlighted the changing reference frame (ie acceleration) as the key discriminant.

Worth noting that "the changing reference frame" bit is not quite exactly incorrect, but it is carelessly worded, and that is one of the common sources of confusion when misunderstood. When we do the calculations properly, there's no change of reference frame, everything is done within the same reference frame - but no matter which reference frame we choose, the velocity of the traveller in that frame changes and the velocity of the earth does not.

 

[Dale]

There's no single, correct way to explain the twin paradox.

That is one reason that the Usenet article is so valuable:

https://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

 

[gen x]

The idea that Richard Feynman didn't understand the basics of relativity as well as anyone else who ever lived is cretinous.

if it is just click bait then no need to further explanation.
I learn from this forum Einstein and Newton was wrong in so many things, so I thought it can be Feynman as well..

Why do you watch you tube videos instead of studying physics textbooks?

Because I don't want to learn physics that will be different for 100 years.

 

[renormalize]

Why do you watch you tube videos instead of studying physics textbooks?

Because I don't want to learn physics that will be different for 100 years.

Explain how learning from YouTube videos instead of textbooks assures that you "...don't...learn physics that will be different for 100 years." Please be specific in your answer.

 

[Histspec]

Worth noting that "the changing reference frame" bit is not quite exactly incorrect, but it is carelessly worded, and that is one of the common sources of confusion when misunderstood. When we do the calculations properly, there's no change of reference frame, everything is done within the same reference frame - but no matter which reference frame we choose, the velocity of the traveller in that frame changes and the velocity of the earth does not.

In defense of Laue it should be clarified that he was talking about changing frames in which the clocks were at rest (in The principle of relativity, 1913), p.43:

Indeed we can decide, which one of the clocks was steadily at rest in one and the same reference system, and which one was in the meantime at rest in two or more such systems.

 

[Sagittarius A-Star]

Because I don't want to learn physics that will be different for 100 years.

Here you can find good youtube videos with lectures of Professor Susskind:
https://theoreticalminimum.com/courses

For some of his lectures also (new enough) text books exist.

 

[PeterDonis]

Because I don't want to learn physics that will be different for 100 years.

There's no place you can go to learn any such thing. But you'll get a lot closer to it learning from textbooks and peer-reviewed papers than you will learning from YouTube videos.

 

[Nugatory]

if it is just click bait then no need to further explanation.
I learn from this forum Einstein and Newton was wrong in so many things, so I thought it can be Feynman as well..

If that’s what you’ve taken away from this forum we have done something very wrong…. Especially because we’ve already pointed you at Asimov’s “Relativity of Wrong” essay.

Because I don't want to learn physics that will be different for 100 years.

Physics will be different a hundred years from now, just as right now it is different from a hundred years ago. But every step forward is an extension, not a replacement, and you have zero chance of understanding new developments without a solid foundation in what we have now.

 

[Dale]

every step forward is an extension, not a replacement

Wow. Very well said!

 

[PeterDonis]

every step forward is an extension, not a replacement

Once a field becomes a science, yes.

I think it's worth noting, though, since no doubt at least some readers have read Thomas Kuhn, that there is a transition that fields go through which is not really an extension. In physics, that happened more or less when Newtonian physics came along. (Note that here I'm separating physics from astronomy, although in the modern view the two are very closely related.) Before that, we had what might be called Aristotelian physics. Newtonian physics is not an extension of Aristotelian physics; it's a replacement.

A similar transition occurred in chemistry, from concepts like phlogiston and caloric to the Lavoisier theory of combustion and all that followed from that.

This was the kind of transition Kuhn was preoccupied with and called a "paradigm shift". But then he went (IMO) off the rails by trying to apply it to every transition everywhere in science, which of course doesn't work. Relativity is an extension of Newtonian physics, not a replacement. As Steven Weinberg once remarked, if you have one of those T-shirts with Maxwell's Equations on it (I used to have one but it wore out, I should probably get another one ), you might have to worry about it going out of style (which assumes that it ever was in style to begin with, a dubious assumption, but let that pass...), but not about its becoming false.

 

[robphy]

Why do you watch you tube videos instead of studying physics textbooks?

Because I don't want to learn physics that will be different for 100 years.

In my experience, YouTube videos may
-on occasion- suggest an interesting way of looking at particular aspect not found in a physics textbook,
which would be appreciated by someone who has studied from the physics textbook.

However, I feel that
-most of the time- the "physics from YouTube videos" and "physics from pop-science"
reminds me of playing the game of "telephone",
where the words are mostly there (maybe packaged into profound catch-phrases)
but the meanings are often distorted enough to be incomplete, ambiguous, or wrong.

"Physics in 100 years" will reference items in physics textbooks and physics papers,
not items from a YouTube video.

For me pop-science (and maybe YouTube if it were around when I was much younger)
was motivation to me to track down-not bypass-those real physics textbooks.
What is the current situation? And in spite of how successful it has been, what are the problems?
While prose and catchy-phrases may be exciting and sound impressive,
they aren't the appropriate tools to solve physics problems and make any real progress.

 

[Hornbein]

. As Steven Weinberg once remarked, if you have one of those T-shirts with Maxwell's Equations on it (I used to have one but it wore out, I should probably get another one ), you might have to worry about it going out of style (which assumes that it ever was in style to begin with, a dubious assumption, but let that pass...), but not about its becoming false.

Maxwell originally had about 20 equations using quaternions. That went out of style.

 

[PeterDonis]

Maxwell originally had about 20 equations using quaternions. That went out of style.

I'm glad it got reduced to 4. (One thing I never found out was whether anyone had made a T-shirt with the tensor formulation, which would have reduced it to two.) Maxwell's original 20 would never have fit on a T-shirt.

 

[Hornbein]

I'm glad it got reduced to 4. (One thing I never found out was whether anyone had made a T-shirt with the tensor formulation, which would have reduced it to two.) Maxwell's original 20 would never have fit on a T-shirt.

Progress. The geometric algebra people got it down to one. But I thought that was silly because in order to do anything useful you have to unpack it.