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Author Topic:   Misconceptions in Relativity
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 1 of 141 (503673)
03-21-2009 4:50 AM


Over at THE END OF EVOLUTION thread, Lucy the Ape claimed that I had stated that "mass increases with velocity", and that I was wrong. Well, if I had ever made such a vague statement, I would probably have to agree that it is wrong. But equally wrong would be the statement "mass does not increase with velocity". Both are "wrong" in their vagueness, and both can be correct given the right context.
This thread is to explore and banish the myriad of misconceptions that arise in Relativity (and related physics areas). We can look at the "paradoxes" of Special Relativity, revisit Percy's favourite topic of cosmological vs doppler red-shift, and delve into black holes, wormholes and time-travel... QM could do with a thread of its own, but there could well be some overlap.
The idea is for brief responses that may lead, if interest dictates, to new threads on specific topics. I would prefer not to get bogged down in any one area in this thread. My time can be limited, so hopefully Son Goku can jump in and help, plus anyone else who thinks they can clarify a situation. But as it is a thread on banishing misconceptions, I will not be pulling any punches if replies start to exacerbate those misconceptions
Lucy the Ape has introduced our first misconception, so I suggest we start there...
Big Bang and Cosmology, please...
Edited by cavediver, : No reason given.

Replies to this message:
 Message 3 by shalamabobbi, posted 03-21-2009 12:57 PM cavediver has replied
 Message 20 by onifre, posted 04-07-2009 12:26 PM cavediver has replied

  
AdminNosy
Administrator
Posts: 4754
From: Vancouver, BC, Canada
Joined: 11-11-2003


Message 2 of 141 (503709)
03-21-2009 9:59 AM


Thread moved here from the Proposed New Topics forum.

  
shalamabobbi
Member (Idle past 2848 days)
Posts: 397
Joined: 01-10-2009


Message 3 of 141 (503720)
03-21-2009 12:57 PM
Reply to: Message 1 by cavediver
03-21-2009 4:50 AM


voyager anomaly
Hi CD,
Thanks for the educational threads.
It seems that on a certain forum run by YECs that much is being made of the voyager anomaly. It appears that your arch nemesis Russell Humphreys has put the anomaly to good use to support his theory and book "Starlight and Time".
Despite the fact that the anomaly is thought to be due to some aspect of the craft, such as radiation of thermal energy etc, and that another craft is planned to investigate this phenomenon, it seems some YECs are busy slapping themselves on the backs over this.
My question is if another experiment verifies the anomaly what modifications to cosmological understanding will likely result from this knowledge? Would the 'tired light' explanation of red shift take over or would something else result?
Thanks.
Edited by shalamabobbi, : wrong word replaced with it's correct cousin.

This message is a reply to:
 Message 1 by cavediver, posted 03-21-2009 4:50 AM cavediver has replied

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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 4 of 141 (503730)
03-21-2009 3:59 PM
Reply to: Message 3 by shalamabobbi
03-21-2009 12:57 PM


Re: voyager anomaly
Oh great - I log in from Heathrow Terminal 4, looking forward to something nice and simple, and I get this Russell Humphreys seems to have a bad case of Lying for Jesus(TM) or perhaps Deluded for Jesus(c). Explaining why however is rather a large topic, as is the whole Pioneer Anomaly, if we are to treat this exhaustively. Far more sensible is to just wait for better data, but that does leave the YECs room to jabber incoherently... I'll see how much time I have to put something together over my vacation this week.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 5 of 141 (503741)
03-21-2009 6:21 PM
Reply to: Message 4 by cavediver
03-21-2009 3:59 PM


Re: voyager anomaly
Hey cavediver,
Explaining why however is rather a large topic, as is the whole Pioneer Anomaly, if we are to treat this exhaustively. Far more sensible is to just wait for better data, ...
So I take it there is no new information on these anomalies?
Pioneer anomaly - Wikipedia
quote:
It appears to cause a constant sunward acceleration of (8.74 1.33) 10−10 m/s2 for both spacecraft. If the positions of the spacecraft are predicted one year in advance based on measured velocity and known forces (mostly gravity), they are actually found to be some 400 km closer to the sun at the end of the year. The magnitude of the Pioneer effect is numerically quite close to the product of the speed of light and the Hubble constant, but the significance of this, if any, is unknown. Gravitationally bound objects such as the solar system, or even the galaxy, do not partake of the expansion of the universe this is known both from theory[1] and by direct measurement.[2]
Data from the Galileo and Ulysses spacecraft indicate a similar effect, although for various reasons (such as their relative proximity to the Sun) firm conclusions cannot be drawn from these sources. These spacecraft are all partially or fully spin-stabilised.
The effect is much harder to measure accurately with craft that use thrusters for attitude control. These spacecraft, such as the Voyagers, acquire small and unpredictable changes in speed as a side effect of the frequent attitude control firings. This 'noise' makes it impractical to measure small accelerations such as the Pioneer effect.
The Cassini mission also had reaction wheels for attitude control, thus avoiding this particular problem, but also had radioisotope thermoelectric generators (RTGs) mounted close to the spacecraft body, radiating kilowatts of heat in hard-to-predict directions. The measured value of unmodelled acceleration for Cassini is (26.7 1.1) 10−10 m/s2, roughly three times as large as the Pioneer acceleration. Unfortunately, the measured value is the sum of the uncertain thermal effects and the possible anomaly. Therefore the Cassini measurements neither conclusively confirm nor refute the existence of the anomaly.[3]
As I recall, approximately the same acceleration would explain the rotation of galaxies without dark matter, but I can't find confirmation of that here.
Galaxy rotation curve - Wikipedia
quote:
The rotation curve of a galaxy can be represented by a graph that plots the orbital velocity of the stars or gas in the galaxy on the y-axis against the distance from the center of the galaxy on the x-axis. Stars revolve around the center of galaxies at a constant speed over a large range of distances from the center of the galaxy. Thus they revolve much faster than would be expected if they were in a free Newtonian potential. The galaxy rotation problem is this discrepancy between the observed rotation speeds of matter in the disk portions of spiral galaxies and the predictions of Newtonian dynamics considering the visible mass. This discrepancy is currently thought to betray the presence of dark matter that permeates the galaxy and extends into the galaxy's halo. An alternative (less favored) explanation is a modification of the laws of gravity, MOND.[1]
There are a limited number of attempts to find alternative explanations to dark matter to explain galaxy rotation curves. One of the most discussed alternatives is MOND (Modified Newtonian Dynamics), originally proposed as a phenomenological explanation back in 1983 but which has been seen to have predictive power in the rotation curves of LSB galaxies. This posits that the physics of gravity changes at large scale but, until recently, was not a relativistic theory. However, this changed with the development of the tensor-vector-scalar gravity (TeVeS) theory[7]. A more successful alternative is the modified gravity (MOG) theory of Moffat such as scalar-tensor-vector gravity (STVG)[8]. Brownstein and Moffat (astro-ph/0506370) applied MOG to the question of galaxy rotation curves, and presented the fits to a large sample of over 100 low surface brightness (LSB), high surface brightness (HSB) and dwarf galaxies[9]. Each galaxy rotation curve was fit without dark matter using only the available photometric data (stellar matter and visible gas) and alternatively a two-parameter mass distribution model which made no assumption regarding the mass to light ratio. The results were compared to MOND and were nearly indistinguishably right out to the edge of the rotation curve data, where MOND predicts a forever flat rotation curve, but MOG predicts an eventual return to the familiar inverse-square gravitational force law. Although these alternatives are not yet considered by the astronomical community to be as convincing as the dark matter model [10], gravitational lensing studies may provide the means to separate the predictions of alternative gravity theories from the dark matter explanation. Recently, observations of the Bullet Cluster have cast considerable doubt on the ability for MOND and other dark matter alternatives to explain the spatial distribution of matter (convergence kappa-map) and ICM gas (surface density Sigma-map).
Would that be a fair summary of the current status?
I don't want to stir up old issues here, just want to keep up to date.
Enjoy.

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 4 by cavediver, posted 03-21-2009 3:59 PM cavediver has replied

Replies to this message:
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WaveDancer
Member (Idle past 5404 days)
Posts: 37
From: NSW Australia
Joined: 09-14-2008


Message 6 of 141 (503987)
03-23-2009 8:24 PM


I have a question! Is time and space the fourth dimension when people talk about the 10,11 or 12 dimensions or is it only the fourth dimension in special relativity and is not considered the fourth dimension anywhere else?

Replies to this message:
 Message 7 by cavediver, posted 03-24-2009 3:59 AM WaveDancer has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 7 of 141 (504030)
03-24-2009 3:59 AM
Reply to: Message 6 by WaveDancer
03-23-2009 8:24 PM


Dimensions in Relativity
Is time and space the fourth dimension when people talk about the 10,11 or 12 dimensions
We're all familiar with the three dimensions of normal existence, e.g. x,y,z or height, width, depth. Relativity introduces time as the fourth dimension, but those of us who work with Relativity almost always put time first - so (t,x,y,z) is a point in space-time, and time is the first dimension. When we start working with extra dimensions in Kaluza-Klein theory, Supergravity, or most recently String Theory, we are adding extra space dimensions, so we have (t,x1,x2,x3,x4,x5,x6,x7,x8,x9) which is a point in 10d space-time.
Rarely, we may add a second (or more) dimension(s) of time, but this is now adding another level of complexity, and opening a whole new can of worms...

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 Message 6 by WaveDancer, posted 03-23-2009 8:24 PM WaveDancer has replied

Replies to this message:
 Message 11 by WaveDancer, posted 03-25-2009 8:52 AM cavediver has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 8 of 141 (504031)
03-24-2009 4:07 AM
Reply to: Message 5 by RAZD
03-21-2009 6:21 PM


Re: voyager anomaly
Would that be a fair summary of the current status?
Well, it's my current level of knowledge - there may be more I can find out once I am back from vacation.

This message is a reply to:
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Son Goku
Inactive Member


Message 9 of 141 (504042)
03-24-2009 7:29 AM
Reply to: Message 5 by RAZD
03-21-2009 6:21 PM


Re: voyager anomaly
The Pioneer Anomaly is probably not gravitational in origin. This is because we can test the semi-major axis of Neptune and Uranus extremely pricisely. If there was a gravitational origin to the anomaly then it would have an affect on the axis of the two planets.
More details here:
http://arxiv.org/abs/gr-qc/0608127
I should mention that these tests are model independant, that is they don't assume any theory of gravity in particular in order to carry out the observations.
This paper is from 2006, as of 2009 the Pioneer Anomaly is consider to be almost certainly not of gravitational origin.
Edited by Son Goku, : Repeated phrasing removed.

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RAZD
Member (Idle past 1405 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 10 of 141 (504146)
03-24-2009 8:14 PM
Reply to: Message 9 by Son Goku
03-24-2009 7:29 AM


Re: voyager anomaly
Interesting. Any idea what the best candidate is at this point?
Thanks

we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


• • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •

This message is a reply to:
 Message 9 by Son Goku, posted 03-24-2009 7:29 AM Son Goku has not replied

  
WaveDancer
Member (Idle past 5404 days)
Posts: 37
From: NSW Australia
Joined: 09-14-2008


Message 11 of 141 (504206)
03-25-2009 8:52 AM
Reply to: Message 7 by cavediver
03-24-2009 3:59 AM


Re: Dimensions in Relativity
Thanks Cavediver.
So for your average Joe time would be considered the 4th dimension.
Just another thing if you get a chance can you or somebody else knowledgeable on the subject watch this video and tell me whether or not it describes the 10 dimensions correctly or does it over simplify it? https://www.youtube.com/watch?v=XjsgoXvnStY

This message is a reply to:
 Message 7 by cavediver, posted 03-24-2009 3:59 AM cavediver has replied

Replies to this message:
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cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 12 of 141 (504222)
03-25-2009 11:57 AM
Reply to: Message 11 by WaveDancer
03-25-2009 8:52 AM


Re: Dimensions in Relativity
So for your average Joe time would be considered the 4th dimension.
Yes.
The video is almost complete nonsense, so please ignore it.

This message is a reply to:
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Replies to this message:
 Message 13 by rueh, posted 03-26-2009 2:14 PM cavediver has replied

  
rueh
Member (Idle past 3661 days)
Posts: 382
From: universal city tx
Joined: 03-03-2008


Message 13 of 141 (504296)
03-26-2009 2:14 PM
Reply to: Message 12 by cavediver
03-25-2009 11:57 AM


photons at the moment of BB
Hello Cavediver,
I have a question for you. A friend and I were discussing the order of events of the BB. My question is. Would there have been light emmitted during the intial moment of the BB, or would light not have been present until after the cosmic dark ages had come to an end, with the formation of stars?
Edited by rueh, : subject correction

'Qui non intelligit, aut taceat, aut discat'
The mind is like a parachute. It only works when it is open.-FZ
The industrial revolution, flipped a bitch on evolution.-NOFX

This message is a reply to:
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Replies to this message:
 Message 14 by cavediver, posted 04-01-2009 7:57 AM rueh has replied

  
cavediver
Member (Idle past 3643 days)
Posts: 4129
From: UK
Joined: 06-16-2005


Message 14 of 141 (504659)
04-01-2009 7:57 AM
Reply to: Message 13 by rueh
03-26-2009 2:14 PM


Re: photons at the moment of BB
Hi, sorry for late response - been diving for a week
Would there have been light emmitted during the intial moment of the BB
No, for the simple reason that there was no such thing as light at that point - photons did not exist. They are a result of electroweak symmetry breaking, which did not occur for around 10-12seconds after the big bang - ages in Big Bang terms After thjat, photons were around but "light" as we think of it - free passage of photons through space - did not occur until recombination, some 380,000 years after the BB.

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Replies to this message:
 Message 15 by rueh, posted 04-01-2009 8:10 AM cavediver has replied

  
rueh
Member (Idle past 3661 days)
Posts: 382
From: universal city tx
Joined: 03-03-2008


Message 15 of 141 (504660)
04-01-2009 8:10 AM
Reply to: Message 14 by cavediver
04-01-2009 7:57 AM


Re: photons at the moment of BB
Thank you for the response. I have been trying to explain this to my friend. However I seem to lack the aptitude to convey, that even though there were photons they would not have produced light as we know it. The photons would have been interacting with charged particles in the universe and would not have been able to travel freely until the universe decoupled and took on a nuetral charge, there by allowing the photons to travel freely. Is this still on the right track so far?

'Qui non intelligit, aut taceat, aut discat'
The mind is like a parachute. It only works when it is open.-FZ
The industrial revolution, flipped a bitch on evolution.-NOFX

This message is a reply to:
 Message 14 by cavediver, posted 04-01-2009 7:57 AM cavediver has replied

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