Undergrad Battery life on VERY fast moving object

[davidjoe]

Photons indeed, I hear you. No time passes in their frame at C, therefore possibly, no distance, could have been traveled, either.

 

[Sagittarius A-Star]

in their frame at C

Such a frame does not exist, because light moves at speed $c$ with reference to each inertial frame.

 

[davidjoe]

Such a frame does not exist, because light moves at speed $c$ with reference to each inertial frame.

I might have worded it better by saying if they travel at C and they measure no time passing, a nullity for them, they don’t perceive a distance traveled, either, distance being speed X time.

 

[Sagittarius A-Star]

I might have worded it better by saying if they travel at C and they measure no time passing, a nullity for them, they don’t perceive a distance traveled, either, distance being speed X time.

Such a measurement is not possible. For measuring time, you need a clock. For measuring distance, you need a ruler. Both have mass and therefore cannot move at the speed of light.

 

[Ibix]

No time passes in their frame at C, therefore possibly, no distance, could have been traveled, either.

There is a flaw in the chain of logic used to reach this view: it turns out you need two vectors that are each timelike, spacelike and null all at once. This is a self-contradiction, and reasoning from there is meaningless. That's how you end up with zen-sounding statements about how light moves without moving in no time - it genuinely is nonsense.

You cannot even define proper time for a pulse of light - it simply doesn't make sense. It's not that they experience zero time, it's that "experience" simply isn't a concept that applies. (And not merely because only humans experience, yadda yadda - because the concept of "time for a pulse of light" is a contradiction in terms.)

 

[davidjoe]

There is a flaw in the chain of logic used to reach this view: it turns out you need two vectors that are each timelike, spacelike and null all at once. This is a self-contradiction, and reasoning from there is meaningless. That's how you end up with zen-sounding statements about how light moves without moving in no time - it genuinely is nonsense.

You cannot even define proper time for a pulse of light - it simply doesn't make sense. It's not that they experience zero time, it's that "experience" simply isn't a concept that applies. (And not merely because only humans experience, yadda yadda - because the concept of "time for a pulse of light" is a contradiction in terms.)

I absolutely follow what you are saying and wonder if there is some intentional mystification of physics, especially in what I would call popular culture theoretical physics, going on. By this I do mean the zen like statements, and or focusing on paradoxical or apparently paradoxical aspects of physics.

Unrelated question, but do you think the popular (high viewership) personalities in physics and astrophysics really do dig into the math and/or push intellectual boundaries? I do realize this is very generally asked, I just don’t want to name specific individuals.

I do credit them for intriguing many and provoking thought processes in their general consumption releases. But for example, you would never glean that a photon is a controversial subject at all, from simply reading and watching current discussions about it, where it’s dealt with as a mundane, pat, known quantity.

 

[Drakkith]

I absolutely follow what you are saying and wonder if there is some intentional mystification of physics, especially in what I would call popular culture theoretical physics, going on. By this I do mean the zen like statements, and or focusing on paradoxical or apparently paradoxical aspects of physics.

Yes, pop-sci is generally oversimplified and overly focused on the 'big flashy stuff' like you say. Articles and videos are also almost always written/produced by someone who isn't and expert in the topic area, and even the ones that are authored by an expert are still usually oversimplified so that people can understand it.

Unrelated question, but do you think the popular (high viewership) personalities in physics and astrophysics really do dig into the math and/or push intellectual boundaries? I do realize this is very generally asked, I just don’t want to name specific individuals.

In their day-to-day work, sure. In their videos, articles, and other types of communication, no.

 

[Nugatory]

I absolutely follow what you are saying and wonder if there is some intentional mystification of physics, especially in what I would call popular culture theoretical physics, going on. By this I do mean the zen like statements, and or focusing on paradoxical or apparently paradoxical aspects of physics.

It’s not intentional mystification, it is the undesired but unavoidable consequence of not using math to describe things that can only be precisely described by math.

Unrelated question, but do you think the popular (high viewership) personalities in physics and astrophysics really do dig into the math and/or push intellectual boundaries? I do realize this is very generally asked, I just don’t want to name specific individuals.

Look at their CV. No one gets a physics PhD or a tenure-track position in a physics department without having really dug into the math and making some original contribution.

But for example, you would never glean that a photon is a controversial subject at all, from simply reading and watching current discussions about it, where it’s dealt with as a mundane, pat, known quantity.

Photons are not a controversial subject, just one that is impossible to discuss clearly without math. But the populizers are not trying to mislead, they’re doing the best they can with inadequate descriptive tools.

 

[PeterDonis]

No time passes in their frame at C, therefore possibly, no distance, could have been traveled, either.

if they travel at C and they measure no time passing, a nullity for them, they don’t perceive a distance traveled, either, distance being speed X time.

Neither of these statements are correct.

 

[davidjoe]

Neither of these statements are correct.

I know, rulers and clocks can’t reach C . Very, very literal construction guys, but I think if I were to take photons out of the statement, and just utilize people instead, which otherwise do perceive the passage of time and distance, it would be “fair” or fairer at least, to say that they, with anything else, would no longer perceive the passage of any time or distance at C. Realizing that it will be said they cannot reach C, I’ll go ahead and agree in advance, though it’s still a true statement the perception of time or distance travelled would stop at that point, and slow, to very nearly stop, extremely close to it.

I’m soft in understanding on the subject of the boundaries of reference frames. CERN for example is intuitively clear acceleration and velocity, relative to us. It’s less clear to me, after that and on large scales.

Math as a representation of relationships and a prediction of positions isn’t inherently problematic for me, I don’t shy away from it, but I don’t use it daily, and haven’t formally honestly since the 90’s. But, I notice from several posts that the plural is maths, now, and that does make me feel old, as that word usage is peculiar to me and would have been unacceptable as the plural of math was math, as of my last course, about 1992. Can I ask if 52 is on average, about a generation or more older than most members here?

 

[PeterDonis]

Very, very literal construction guys

No, it's physics. Your dismissive attitude here is not going to get you anywhere. Physics is not done by waving your hands. It's done by understanding its laws.

I think if I were to take photons out of the statement, and just utilize people instead, which otherwise do perceive the passage of time and distance, it would be “fair” or fairer at least, to say that they, with anything else, would no longer perceive the passage of any time or distance at C.

No, you wouldn't, because people cannot move at C. People are timelike objects; photons are lightlike objects. Those are two physically different kinds of things, and concepts like "perceive the passage of time and distance" only apply to timelike objects. They do not apply to lightlike objects. That is the physics; that is what the laws of relativity say. You can either accept that and try to understand it, or dismiss it and end up having your thread closed.

Realizing that it will be said they cannot reach C, I’ll go ahead and agree in advance, though it’s still a true statement the perception of time or distance travelled would stop at that point

No, it is not a true statement, it's a false one. You really, really, really need to learn what the laws of relativity actually say instead of continuing to make baseless wrong claims.

and slow, to very nearly stop, extremely close to it.

This is not correct either. The correct statement is that "rate of time flow" as you are using the term here has no physical meaning. You, right now, are moving at 0.9999999c relative to cosmic ray particles reaching Earth. Is your time slowed? No. That is the physics. The "time dilation" of you relative to the cosmic ray particles is just a coordinate artifact.

I’m soft in understanding on the subject of the boundaries of reference frames.

Then you should definitely not be making such confident statements about what you think relativity says. You should not be making statements at all.

Can I ask if 52 is on average, about a generation or more older than most members here?

I can't speak for other members, but you are younger than me by a number of years. And my last formal course in anything, including math, was about four years before your last one.

 

[PAllen]

unacceptable as the plural of math was math, as of my last course, about 1992. Can I ask if 52 is on average, about a generation or more older than most members here?

My last math course was in 1973 and I am a couple of decades older than you.

 

[renormalize]

But, I notice from several posts that the plural is maths, now, and that does make me feel old, as that word usage is peculiar to me and would have been unacceptable as the plural of math was math, as of my last course, about 1992.

https://www.thesaurus.com/e/grammar/math-vs-maths/
"The only difference between math and maths is where they’re used. Math is the preferred term in the United States and Canada. Maths is the preferred term in the United Kingdom, Ireland, Australia, and other English-speaking places."

 

[davidjoe]

No, it's physics. Your dismissive attitude here is not going to get you anywhere. Physics is not done by waving your hands. It's done by understanding its laws.


No, you wouldn't, because people cannot move at C. People are timelike objects; photons are lightlike objects. Those are two physically different kinds of things, and concepts like "perceive the passage of time and distance" only apply to timelike objects. They do not apply to lightlike objects. That is the physics; that is what the laws of relativity say. You can either accept that and try to understand it, or dismiss it and end up having your thread closed.


No, it is not a true statement, it's a false one. You really, really, really need to learn what the laws of relativity actually say instead of continuing to make baseless wrong claims.


This is not correct either. The correct statement is that "rate of time flow" as you are using the term here has no physical meaning. You, right now, are moving at 0.9999999c relative to cosmic ray particles reaching Earth. Is your time slowed? No. That is the physics. The "time dilation" of you relative to the cosmic ray particles is just a coordinate artifact.


Then you should definitely not be making such confident statements about what you think relativity says. You should not be making statements at all.


I can't speak for other members, but you are younger than me by a number of years. And my last formal course in anything, including math, was about four years before your last one.

I’m not trying to be argumentative with you, but this excerpt is literally Microsoft Bing’s first hit on the subject, highlights are not mine.

 

[davidjoe]

This is the article.

 

[PeterDonis]

I’m not trying to be argumentative with you, but this is excerpt is literally Microsoft Bing’s first hit on the subject, highlights are not mine.

I'm not trying to be argumentative with you either, but you should know that doing random Internet searches is not a good way to learn physics. You need to be learning from textbooks and peer-reviewed papers.

This is the article.

Nothing you provided gives a link to any article.

 

[PAllen]

I’m not trying to be argumentative with you, but this excerpt is literally Microsoft Bing’s first hit on the subject, highlights are not mine.


View attachment 342883

Bing is a search engine. It finds nonsense just as easily as good science. Actually, it is skewed towards bad science, since there is more of this on the internet, so its weighting ends up favoring bad science.

The above statements are a mixture of just wrong and totally meaningless.

 

[Nugatory]

I’m not trying to be argumentative with you, but this is excerpt is literally Microsoft Bing’s first hit on the subject, highlights are not mine.

Not everything you find on the internet is correct, and not everything correct is highly ranked by the search engines. In this case Bing is serving highly ranked incorrect content.

 

[davidjoe]

I don’t know enough to disagree with you, I only know I’m not saying something that I have not understood, from other sources.

 

[Drakkith]

I know, rulers and clocks can’t reach C . Very, very literal construction guys, but I think if I were to take photons out of the statement, and just utilize people instead, which otherwise do perceive the passage of time and distance, it would be “fair” or fairer at least, to say that they, with anything else, would no longer perceive the passage of any time or distance at C. Realizing that it will be said they cannot reach C, I’ll go ahead and agree in advance, though it’s still a true statement the perception of time or distance travelled would stop at that point, and slow, to very nearly stop, extremely close to it.

Some issues: Reference frames are relative. If something is moving at .5c relative to us, then we are moving at 0.5c relative to it. So statements about what light may or may not being doing in a reference frame moving at c relative to us would force us to be moving at c relative to light. Which introduces some problems to which the only solution that is self-consistent is that light cannot be assigned a reference frame and any talk of the passage of time for objects moving at c is meaningless.

I don’t know enough to disagree with you, I only know I’m not saying something that I have not understood, from other sources.

Any source that talks about light as having a reference frame is wrong. It doesn't and any attempt to do so introduces severe problems.

 

[PeterDonis]

I don’t know enough to disagree with you

Indeed.

I only know I’m not saying something that I have not understood, from other sources.

You might want to read our rules on acceptable sources, which are under "Acceptable Sources" on this page:

https://www.physicsforums.com/threads/physics-forums-global-guidelines.414380/

No source you have referenced is acceptable according to our guidelines.

 

[Sagittarius A-Star]

I don’t know enough to disagree with you, I only know I’m not saying something that I have not understood, from other sources.

Here is a good source:
http://www.scholarpedia.org/article/Special_relativity

 

[davidjoe]

Here is a good source:
http://www.scholarpedia.org/article/Special_relativity

Thank you, I’ll print this at the office and look forward to reading it. I do hope members realize that I was merely reprising that passage in response to the comment on my basis for my prior comments, and not as an advocate for its truth in comparison to the veracity of other resources. I’ll add that positions in that excerpt do seem to be commonly held views often reproduced in whole or part, and certainly I over years have had enough exposure to them to be assuming it was accepted thought, when it evidently is not at all, and is actually considered to be inaccurate, and as said I openly do not have reason to disagree.

I have tried to do the opposite of confidently staking out the truth of any positions let alone novel ones, by saying several times already in my short experience here, that I am not in this field, I’ve been an attorney since 1997 (not a natural science field) and my thoughts are expressions and discussion based only on what I have gleaned is the current thought, from consumer grade, readily and widely accessible sources, with my own inferences drawn from them, and characterized that way. I certainly didn’t believe them (such as the excerpt on experiencing time stoppage at C above) to be either controversial or wrong, and I do appreciate that, now. It is a valuable lesson and well taken.

 

[Sagittarius A-Star]

Thank you, I’ll print this at the office and look forward to reading it.

I think this is a good idea. I like this text. However, please be aware, that Wolfgang Rindler used in the chapter about relativistic mechanics the "relativistic mass", which is today considered an out-dated terminology.

A WORD OF CAUTION: there is a school of thought (mainly among particle physicists who, after all, are the main consumers of collision mechanics) who reject the concept of relativistic mass altogether. Wherever we have an $m_u$, they would replace it by $E/c^2$ ; our $m_0$ becomes their $m$, simply called the mass; and our $E=m_uc^2$ becomes their $E=\gamma(u)mc^2$. This has nothing to do with physics. It is simply a choice between two alternative conventions

Source:
http://www.scholarpedia.org/article/Special_relativity:_mechanics#The_equivalence_of_mass_and_energy

A discussion of it:
https://edisciplinas.usp.br/pluginfile.php/7731007/mod_resource/content/1/Rindler-et-al-1990.pdf

 

[jbriggs444]

widely accessible sources, with my own inferences drawn from them

A serious and, perhaps, unavoidable problem with widely accessible sources is that in order to be accessible and understandable without careful definitions and mathematics, things are simplified. Often oversimplified. Explained with heavy use of analogy.

If the idea is to provide a bit of flavor, some amusement and awestruck wonder, this is no problem. The audience gets what they came to see.

However, oversimplification and analogy does not work as a basis from which to reason further. It is unreliable and utterly worthless as a jumping off point for an actual understanding. It is just one more layer to unlearn before an actual education can begin. You cannot trust the conclusions you reach by reasoning further from what you think you have learned in a popular video.

 

[Sagittarius A-Star]

Effect of time dilation when distance between two objects remains constant

For the following I assume, that the usable electric energy in the battery is neglectable small compared the the rest-energy of the rocket, so that the laser emission does not significantly change the velocity of the rocket.

The rocket moved momentarily with $v$ in $x$-direction and emits a laser pulse in $y$-direction towards the planet (transversal Doppler shift in the receiver's frame).

The 4-momentum of the laser pulse in the (unprimed) planet's frame is is $\mathbf P = \begin{pmatrix} p_{ct} \\ p_x \\ p_y \\ p_z \end{pmatrix} = {E \over c^2} \begin{pmatrix} c \\ 0 \\ c \\ 0 \end{pmatrix}$

Lorentz-transformation into the (primed) rocket's frame:

$p'_{ct} = \gamma (p_{ct} - {v \over c} p_x) = \gamma {E \over c} = c\delta m$
$p'_{x} = \gamma (p_{x} - {v \over c} p_{ct}) = -\gamma {E \over c^2}v$
$p'_{y} = p_{y} = {E \over c}$
$p'_{z} = p_{z} = 0$

$\Rightarrow {E \over c^2} = {1 \over \gamma} \delta m$ (=redshift)

Here $\delta m$ is the (rest-)mass-decrease of the battery and $E$ the received energy from the laser-pulse.

 

[Drakkith]

I have tried to do the opposite of confidently staking out the truth of any positions let alone novel ones, by saying several times already in my short experience here, that I am not in this field, I’ve been an attorney since 1997 (not a natural science field) and my thoughts are expressions and discussion based only on what I have gleaned is the current thought, from consumer grade, readily and widely accessible sources, with my own inferences drawn from them, and characterized that way. I certainly didn’t believe them (such as the excerpt on experiencing time stoppage at C above) to be either controversial or wrong, and I do appreciate that, now. It is a valuable lesson and well taken.

Learning physics without looking at the actual math and accepted rules of the theory is like using various web articles and videos about to learn about the law versus actually reading the laws from their official sources. It's fine if you want a summarized overview of what things are likely to be, but I bet you wouldn't be surprised to find a great many of the details wrong or omitted.

 

[davidjoe]

Note that some care is needed with this statement. It's not really correct. A better way to put it is that clocks in motion with respect to sn inertial reference frame tick slowly as measured by clocks at rest in that frame. Thay avoids nasty definitional questions around what "time slowing" might actually mean and grounds everything in physical measurements.

The sentence as written happens to work out in the case in this thread because one clock is moving in a circle at constant speed and one is inertial, but it's not a good general description.

Following up, my understanding is the relativistic speed of the satellite could separate two synchronized clocks, one in the satellite, and one on the surface.

Is speed also relative, as time is, affecting the calculation of orbital speed? For example if the satellite is in low earth orbit, say 150 miles up, seeking to be accelerated to 4 circumferential revolutions per second under ground control, as determined by interrupting say 2 perpendicular beams along its path, equidistant, to level out at 8 interruptions per second, then the satellite levels out at roughly 4/7 C.

4/7 C is a relativistic speed. If the control of the orbiting satellite is not ground based, but instead is performed from the satelite wherby it accelerates and decelerates so as to level out and maintain breaking those two light beams eight times per second according to its clock, to cover the distance required to put its speed at 4/7 C, then its speed won’t be the same as if measured from earth, right? (because the clocks are keeping time differently)

In the original hypothetical 10 minutes (600 seconds) in orbit could equal 30 minutes 1,800 seconds) passing on the ground.

The battery whose life was 10 minutes could be explained to extend to 30 minutes of weaker emission as measured on the ground through red shift but, if both the ground sensors and the ship experience the ship breaking the light beam eight times every second to achieve 4/7 C, how does this reconcile with three times as many seconds passing on the ground?

 

[Drakkith]

4/7 C is a relativistic speed. If the control of the orbiting satellite is not ground based, but instead is performed from the satelite wherby it accelerates and decelerates so as to level out and maintain breaking those two light beams two times per second according to its clock, to cover the distance required to put its speed at 4/7 C, then its speed won’t be the same as if measured from earth, right? (because the clocks are keeping time differently)

Hmm. I wonder how length contraction works into this?

 

[jbriggs444]

For example if the satellite is in low earth orbit, say 150 miles up, seeking to be accelerated to 4 circumferential revolutions per second under ground control, as determined by interrupting say 2 perpendicular beams along its path, equidistant, to level out at 8 interruptions per second, then the satellite levels out at roughly 4/7 C.

So we have a satellite that is orbitting the earth 4 times a second. Meanwhile, light can orbit the earth about 7 times a second. So yes, this is 4/7 C -- as measured from the inertial rest frame of the earth.

4/7 C is a relativistic speed. If the control of the orbiting satellite is not ground based, but instead is performed from the satelite wherby it accelerates and decelerates so as to level out and maintain breaking those two light beams eight times per second according to its clock, to cover the distance required to put its speed at 4/7 C, then its speed won’t be the same as if measured from earth, right? (because the clocks are keeping time differently)

At any instant, the speed of the Earth in the instantaneous rest frame of the satellite will match the speed of the satellite in the rest frame of the Earth. That is 4/7 C.

Things get sticky when you try to shift from the inertial frame where the satellite is momentarily at rest to an accelerating frame where the satellite is continuously at rest. Any such accelerating frame (there is some freedom in choosing how to set one up) is going to be wonky in some way. For instance, if you assume an isotropic speed of light and try to synchronize clocks all the way around the orbital path of the satellite, you'll find that the satellite clock is out of synch with itself.

This is at the heart of the Ehrenfest paradox.

Since length contraction, time dilation and relativity of simultaneity are features that arise when comparing coordinates between inertial frames of reference, it ought to be no surprise that they stop working as expected when blindly applied between an inertial and a non-inertial frame.

It turns out that there is no problem applying the time dilation formula to Earth clocks to compute the elapsed proper time on the satellite. If an orbit takes $\frac{1}{4}$ second as judged by Earth and if the time dilation factor is $\sqrt{1-v^2/c^2}$ for $v=\frac{4}{7}c$ then I make it about 0.2 seconds per "orbit" as measured on the satellite clock. [Elapsed proper time is a direct physical measurable. Not just a convention that is affected by choice of coordinate system]

I am taking "orbit" to mean a low altitude circular equatorial trajectory starting above Quito Equador and then arriving back there again a bit later.