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Time : Expansion of The Universe
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no one knows is my guess.0
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Cú Giobach wrote: »Yes, photons aren't affected by anything until they are absorbed.
The red shift we observe due to expansion is only relative to the observer.
Photons are "unchanging and timeless".
I'm sorry but I'm having trouble with this.
Surely the red-shift is entirely due to the relative speed of the photon to the detector which in the region of the detector is unaffected by expansion.
Suppose a photon is emitted from a galaxy adjacent to ours to be detected on earth. Now, if the distance between the galaxies is increasing at say half a light year per year due to expansion then when the photon arrives at the mid-point between the two galaxies, the distance between the photon and the detector will increase one-quarter light year per year. When the photon covers half the remaining distance, expansion will increase the distance by only an eighth of a light year per year.
In other words, the effect of expansion will be reduced continuously throughout the photon's journey. When that photon arrives at a point that is one light second away from the detector, the effect of expansion becomes negligible. If the rate of expansion has no effect on the photon, why should it be red-shifted at all except as a consequence of the relative velocities of the two galaxies?
If the increase in distance between the two galaxies is due entirely to expansion then photons shouldn't be red-shifted at all, should they?
Do you see what I mean? If galaxies are all receding from each other at the same rate then doesn't that suggest that galaxies have zero velocity of their own and but for expansion, would appear stationary relative to each other?
I mean, if galaxies were accelerating away from each other due to their own velocity, shouldn't the distances between galaxies be increasing more in one direction than another?0 -
TBH, this seems like science imitating religion to me.
I'm sure that Richard's inability to understand the Universe will not impede our attempts to understand the Universe.0 -
It is the relative velocity of the two galaxies that is responsible for the observed red shift (the relative speed between photon and detector is constant, irrespective of the speed of the detector or emitter. 300,000 km/s).I'm sorry but I'm having trouble with this.
Surely the red-shift is entirely due to the relative speed of the photon to the detector which in the region of the detector is unaffected by expansion.
Suppose a photon is emitted from a galaxy adjacent to ours to be detected on earth. Now, if the distance between the galaxies is increasing at say half a light year per year due to expansion then when the photon arrives at the mid-point between the two galaxies, the distance between the photon and the detector will increase one-quarter light year per year. When the photon covers half the remaining distance, expansion will increase the distance by only an eighth of a light year per year.
In other words, the effect of expansion will be reduced continuously throughout the photon's journey. When that photon arrives at a point that is one light second away from the detector, the effect of expansion becomes negligible. If the rate of expansion has no effect on the photon, why should it be red-shifted at all except as a consequence of the relative velocities of the two galaxies?
To show that it is not a change in the nature of a photon consider this, a detector on Earth measures the light from a distant galaxy and gets a redshift of x, now say you have a different detector in a spaceship travelling towards the distant galaxy at a high speed, that detector would measure the light as having a redshift of y, the only change was the speed of the detector, there was nothing to change the actual nature of the photons being detected, yet both methods of measurement would get different results.
Yes, because the wavelength is "stretched" due to expansion, and though expansion on a local level is negligible the wavelength has not been "squeezed" back to its original length just before it hits the detector.If the increase in distance between the two galaxies is due entirely to expansion then photons shouldn't be red-shifted at all, should they?
I don't get what you mean, the velocity of receding galaxies that we measure, is due to expansion.Do you see what I mean? If galaxies are all receding from each other at the same rate then doesn't that suggest that galaxies have zero velocity of their own and but for expansion, would appear stationary relative to each other?
I mean, if galaxies were accelerating away from each other due to their own velocity, shouldn't the distances between galaxies be increasing more in one direction than another?0 -
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TBH, this seems like science imitating religion to me.
I'm sure that Richard's inability to understand the Universe will not impede our attempts to understand the Universe.
Although Sagan did much to popularize the names of many astronomers,he like Feymann tends to have an Orwellian manner in directing the works of astronomers towards ends which those men never intended such as the idea that the furthest galaxies are the oldest which sets the stage for the head wrecking venture of 'big bang'.
Newton's work which really began the speculative/modeling agenda surfaced in 1689 while Roemer's attempt to explain light speed using planetary comparisons emerged in 1676 so Feymann manufactures history to make it appear Roemer was following Newton -
"were ahead of schedule when Jupiter was close to the earth and behind
schedule when it was far away, a rather odd circumstance. Mr. Roemer
[Olaus Roemer, 1644-1710, Danish astronomer], having confidence in the
Law of Gravitation, came to the interesting conclusion that it takes
light some time to travel from the moons of Jupiter to the earth, and
what we are looking at when we see the moons is not how they are now
but how they were the time ago it took light to get here." Feymann
With online tools such as an orrery in tandem with contemporary imaging,observers can now enjoy images of Io and its shadow passing across the face of Jupiter with the gap between Io and its shadow changing as the Earth approaches or recedes from Jupiter or at least,this is what I realized as few years ago. -
http://apod.nasa.gov/apod/ap021207.html
http://apod.nasa.gov/apod/ap990423.html
http://math-ed.com/Resources/GIS/Geometry_In_Space/java1/Temp/TLVisPOrbit.html
There are problems with Ole Roemer's view for fairly technical reasons,one of which is that a full set of Equation of Time tables didn't appear until John Harrison created them over a century later but at least observers interested in astronomy can gain some insight into how Roemer uses the varying distances between Earth and Jupiter to come up with his solution for the anomalous motion of Io .0 -
TBH, this seems like science imitating religion to me.
I'm sure that Richard's inability to understand the Universe will not impede our attempts to understand the Universe.
In fact, he was describing quantum mechanics, which as we know, is the most successful theory put forth in terms of making testable, reliable predictions. In terms of why the predictions work, Feynman was honest enough to admit that he doesn't know. He just knew that they did, as determined by many repeatable experiments.0 -
gkell, ponder this:
Well that is all triumphalism and besides he is paraphrasing Galileo who was talking about geometric proofs and I don't even agree with that either,at least up to a point -
"The laws of Nature are written in the language of mathematics ... the
symbols are triangles, circles and other geometrical figures, without
whose help it is impossible to comprehend a single word." Galileo
Today any reader here can go to time lapse footage or sequential imaging and comprehend astronomical observations and even match them up with the geometrical proofs of astronomers.With Mars presently moving backwards against the background stars as the Earth overtakes it,readers can use contemporary imaging to square it away with Kepler's representation -
http://apod.nasa.gov/apod/ap080511.html
http://en.wikipedia.org/wiki/File:Kepler_Mars_retrograde.jpg
"Copernicus, by attributing a single annual motion to the earth,
entirely rids the planets of these extremely intricate coils ,
leading the individual planets into their respective orbits
,quite bare and very nearly circular. In the period of time
shown in the diagram, Mars traverses one and the same orbit as many
times as the 'garlands' you see looped towards the
centre,with one extra, making nine times, while at the same time the
Earth repeats its circle sixteen times " Kepler
The point here is that contemporary imaging makes the geometric proofs of the older astronomers comprehensible to the interested reader rather than the popular view that mathematics makes the Universe almost incomprehensible.In Feymann's view he is more or less talking himself up rather than talking the listener and student down,you can get away with it but it doesn't make it good or right.0 -
Are you actually trying to say that one of the most prominent physicists of the 20C, a Nobel Laureate no less is wrong ?0
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Cú Giobach wrote: »It is the relative velocity of the two galaxies that is responsible for the observed red shift (the relative speed between photon and detector is constant, irrespective of the speed of the detector or emitter. 300,000 km/s).
Sorry, I was rather under the impression that relative velocity has an effect on momentum and hence energy and that a red-shift is effectively a 'perceived' change of wavelength due to the change in momentum which is the resultant of relative velocity.
Suppose you were to fix two detectors on opposite sides of a spinning disk and that you placed a photon source which emits photons at a constant rate and at a constant energy, 'e', at a distance, 'd', from the axis of rotation.
As the disc spins, the detectors will show a signal that oscillates between red-shift and blue-shift. When the detectors arrive positions that are equidistant from the emitter, the one travelling away from the emitter will show a red-shift and the other which is travelling towards the emitter will show a blue-shift.
But when the detectors arrive at a position where one is at its closest point to the emitter while the other is at its furthest, neither will show any shift at all.
Couldn't this be explained by saying that the detector that shows a blue-shift is encountering more photons per unit of time than the one showing a red-shift and furthermore, the blue-shifted photons are hitting the detector 'harder' than the red-shifted ones?
How can the relative speeds of the photons to the detectors remain constant?Cú Giobach wrote: »To show that it is not a change in the nature of a photon consider this, a detector on Earth measures the light from a distant galaxy and gets a redshift of x, now say you have a different detector in a spaceship travelling towards the distant galaxy at a high speed, that detector would measure the light as having a redshift of y, the only change was the speed of the detector, there was nothing to change the actual nature of the photons being detected, yet both methods of measurement would get different results.
Yes, I can see how that might be the case.Cú Giobach wrote: »Yes, because the wavelength is "stretched" due to expansion, and though expansion on a local level is negligible the wavelength has not been "squeezed" back to its original length just before it hits the detector.
But how can expansion directly affect the wavelength of a photon if it has no effect on the photon? If 'time' and 'distance' cannot be experienced by a photon, how can expansion affect the wavelength?
This seems somehow contradictory.Cú Giobach wrote: »I don't get what you mean, the velocity of receding galaxies that we measure, is due to expansion.
Which suggests that because galaxies are evenly spread (more or less) throughout the Universe, galaxies have little, if any, intrinsic velocity of their own.
If photons are travelling at a velocity 'c' relative to space and galaxies are not moving at all relative to space then when a photon arrives at a detector, it should have the same velocity and energy as it did when it was emitted. i.e., there should be no shift at all.
I'm sorry if this seems a little vague but it is difficult to put this concept into words.0 -
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In fact, he was describing quantum mechanics, which as we know, is the most successful theory put forth in terms of making testable, reliable predictions. In terms of why the predictions work, Feynman was honest enough to admit that he doesn't know. He just knew that they did, as determined by many repeatable experiments.
He spent four and a half minutes telling me absolutely nothing. In fact, most of the talks I've heard from him say a similar thing, 'Don't bother trying to understand or explain it; I can't do it so neither can you.'
It comes across as elitism to me.0 -
AugustusMinimus wrote: »Are you actually trying to say that one of the most prominent physicists of the 20C, a Nobel Laureate no less is wrong ?
Are you saying that makes him infallible?
Like Newton was? Or Einstein?0 -
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Not infallible. But I'll take his word on most physics subjects over gkell's.0
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AugustusMinimus wrote: »Are you actually trying to say that one of the most prominent physicists of the 20C, a Nobel Laureate no less is wrong ?
I present contemporary imaging which matches up with Kepler's representation of the motion of Mars over 16 years and expect only that observers can agree that they do match up in principle for the contemporary sequence of images is a partial representation of Kepler's diagram -
http://en.wikipedia.org/wiki/File:Kepler_Mars_retrograde.jpg
http://apod.nasa.gov/apod/ap080511.html
Holding the cursor on the NASA image unveils the background constellations which match up with the symbols on the outer rim of Kepler's representation.
Unlike Feynmann there were once mathematicians who conceded they didn't know how Newton arrived at his conclusions regarding the work of Kepler yet seemed to be right and that is where contemporary imaging comes in -
"The demonstrations throughout the book [Principia] are geometrical,
but to readers of ordinary ability are rendered unnecessarily
difficult by the absence of illustrations and explanations, and by the
fact that no clue is given to the method by which Newton arrived at
his results." W.W.Rouse Ball 1908
If even one reader here can match the contemporary imaging with Kepler's representation at this important juncture in astronomy and science,they will start to see something new and they may not like it insofar as this is where the great interpretative discipline of astronomy became lost to the predictive/modeling agendas and the celestial arena became a dumping ground for theorists.
This is not a tribunal to find people wrong or corrupt,it provides a picture with as many online tools as is possible to make clear what was not for many centuries whether it is the works of Copernicus and Kepler or the later mutations introduced in the late 17th century.0 -
It's a 4.5-minute excerpt from an hour-long lecture.
I know. I'm sorry if I came across as flippant. I just object a little to being told what I'm not capable of.
And let's face it, there will eventually be a scientist or a discovery that will bring us even closer to understanding the Universe we inhabit.0 -
AugustusMinimus wrote: »Not infallible. But I'll take his word on most physics subjects over gkell's.
Well, someone has to discover the 'next big thing'. Why not gkell? Or you for that matter.
Scientists are only human and have no real advantage over other humans.0 -
Join Date:Posts: 1102
But how can expansion directly affect the wavelength of a photon if it has no effect on the photon? If 'time' and 'distance' cannot be experienced by a photon, how can expansion affect the wavelength?
This seems somehow contradictory.
Because we observe it as a form of time dilation. Can i rephrase your question like this:
"how can increasing distance from a receeding repeating source affect the wavelength of a sound if it has no affect on the sound. If time and distance cannot be experienced by a sound how can increasing distance from a receeding repeating source affect the wavelength. Doppler effect is this time dilation. And it is relativistic.
We are not measuring individual photons. we are measuring the level of shift of a known spectral line of a specific chemical (for example) this signature of a chemical seems to shift in the spectrum of light as the source either approaches us or receeds away from us. The signature remains the same and identifiable.
We are all familiar with the doppler shift of a sound from a siren as it approaches or receeds from an observer not travelling with the siren. The ambulance driver for eg. doesnt perceive a change in wavelength (pitch) of the sound from the source (his siren). but an observer witnessing the ambulance race towards them and race away most certainly does. The sound itself doesnt change (nor does its velocity) just our perception of its intensity as each let me say "new sound wave" is sent as the ambulance is either closer to you with comparison to the time it sent the previous sound wave and vice versa. Thus compacting the amount of sound waves you observe (perceived shorter wavelength/ higher pitch) in the same relative amount of time as it approaches and vice versa respectively. Lets say the driver hears 5 oscillations every 5 seconds of the sound. an observer that the ambulance is approaching will hear more oscillations (a higher pitch) in their 5 seconds. Or less if it is receeding away.
To offer another possibly insulting example:
Say i have a pellet gun that can accelerate pellets to a muzzle velocity of 100 miles a second (and say this velocity remains constant until striking a target, this all occurs in a vacuum so no drag etc. ). Say also i have another observer 100 miles away with a pellet trap that would ping everytime a pellet was fired at it.
With the experiment setup i would proceed to fire 5 shots at 1 second intervals at the target (pellet trap). for every shot the pellet arrives at the target 1 second later. so within my experience of 5 seconds i have shot 5 pellets and within the observers experience of 5 seconds they would have observed 5 pings @ 1 second intervals also although obviously delayed by the 1 second travel time relative to me. So after 5 seconds i know i shot 5 pellets but after 5 seconds for me, the observer would only experience the ping of 4 shots. he would have to wait an additional 1 second for the 5th pellet to arrive at the target. Ok incredibly simple concept to grasp yes, we are both stationary. the space between us did not increase in this example. and the frequency of pellets hitting the target remained the same (1 shot per second) for me and for the observer, as it would with sound waves and light waves.
Now in the next example lets expand the space (increasing distance) between observer and I by 20 miles every second per shot in the opposite direction. I fire 5 shots at 1 seconds intervals at the target. The first pellet strikes the target 1 second later, the second pellet strikes the target 1.2 seconds later. the third pellet 1.4 seconds later. the fourth pellet 1.6 seconds later and the fifth pellet 1.8 seconds later. I fired 5 shots in 5 seconds. The observer observes 5 pings in 7 seconds. a different frequency than i observed. in the same amount of time; 5 seconds for the observer, they only observed 3 pings from the pellet trap. they would have had to wait .2 seconds longer to observe the 4th ping. the frequency of pellets hitting the target decreased for the observer in the same relative amount of time.
Now lets compress the distance by 20 miles ever second per shot toward the observer. i fire 5 shots at 1 second intervals at the target. The first pellet strikes the target 1 second later. the second pellet 0.8 seconds later. the third pellet 0.6 seconds later. the fourth pellet 0.4 seconds later and the fifth pellet 0.2 seconds later. i fired 5 pellets in 5 seconds. the observer observed 5 pings in 3 seconds. a much higher frequency than the source initially observed, me. 5 Seconds passed for me to shoot 5 pellets but only 3 seconds passed for the observer to observe 5 pellets hitting the pellet trap. the observer witnessed events in a shorter time so at a higher frequency.
The intensity of the pings decreased or increased, the pellets didnt change nor did their velocity. their frequency relative to the observer did when accelerating towards or receeding away. Knowing that the pellets had a 100 mile an hour constant velocity the observer could rightly conclude that i was either moving away from them or approaching them considering the difference in frequency of pings that they observed.
We measure the different colours of light as having different frequencies (wavelengths) obviously xrays have much shorter wavelengths than visible light, and visible light has shorter wavelengths than infrared. if the frequency we observe is different, then we see a difference in colour up or down, that known spectrum that is visible to us. if we know the signature of a specific chemical (absorption lines etc.), in the transmission of light from an approaching or receeding source that signature that we have identified, if it has shifted position in the spectrum, we know the signature and how to recognise it so we will see that shift. it will still be the same signature. As it is the same pellet hitting the target.Well, someone has to discover the 'next big thing'. Why not gkell? Or you for that matter.
Scientists are only human and have no real advantage over other humans.
You mean scientists have no real advantage over other scientifically literate humans of course unless you factor in budgets and scientific equipment. For eg. the scientists (particle physicists) at cern have a significant advantage over Irish scientists (irish particle physicists) in the field of particle research because Ireland is not a contributing member of Cern. As will future generations have an advantage over us. they will have had the benefit of more experiments and more results if they continue the scientific method with which to draw conclusions from.0 -
Since Slade_x dealt with your other points, I'll only deal with this one.How can the relative speeds of the photons to the detectors remain constant?
The speed of light is constant, irrespective of the motion of the emitter, and is always measured the same, irrespective of the motion of the observer.
For example, if you were on a spaceship travelling at 10,000 km/s and you shone a beam of light in your direction of travel, the beam would not be travelling at 310,000 km/s, but still at c ie; 300,000 km/s.
And if you were travelling towards a beam of light on a spaceship at 10,000 km/s, you would still measure the speed of the beam as 300,000 km/s.
Check out the "Michelson-Morley experiment", This was one of the biggest ever discoveries in physics, the consequences of which Einstein later dealt with in his theories of relativity.0 -
You mean scientists have no real advantage over other scientifically literate humans of course unless you factor in budgets and scientific equipment. For eg. the scientists (particle physicists) at cern have a significant advantage over Irish scientists (irish particle physicists) in the field of particle research because Ireland is not a contributing member of Cern. As will future generations have an advantage over us. they will have had the benefit of more experiments and more results if they continue the scientific method with which to draw conclusions from.
What you are describing is not science proper but a culture,almost a cult,which often in the face of common sense,will force through conclusions that have no relevance to celestial or terrestrial phenomenon or to human understanding.The person today is asked to believe a particular ideology based on its acceptance by a majority of scientists rather than coming to an individual understanding in the same way people like Galileo,Kepler or anyone here would accept the reasons Copernicus give for the Earth's motions.After receiving an education that the Irish landscape and its biology was influenced by large scale natural temperature changes in remote antiquity ,they now are being forced to accept a majority opinion that humanity has control over global temperatures and despite indifference,it does bother people because it opposes common sense.
An individual comes here and raises an objection to 'big bang',perhaps points out where a proposal doesn't work or goes against the normal behavior of objects in space and either gets a runaround or is told they have yet to reach a certain intellectual level where there is an agreement among scientists.If their point is good they will suffer personal attack,if their point is weak then it will be exploited and they will be made to feel inferior and this is no way to carry on.The point is that when common sense is the issue then something is radically wrong and in a way one of the most important discoveries I made is that it is nothing new,many of the well known scientists wrote about the tendency of a group mentality to run away with itself -
" I have heard such things put forth as I should blush to repeat--not
so much to avoid discrediting their authors (whose names could always
be withheld) as to refrain from detracting so greatly from the honor
of the human race. In the long run my observations have convinced me
that some men, reasoning preposterously, first establish some
conclusion In their minds which, either because of its being their own
or because of their having received it from some person who has their
entire confidence, impresses them so deeply that one finds it
impossible ever to get it out of their heads. Such arguments in
support of their fixed idea as they hit upon themselves or hear set
forth by others, no matter how simple and stupid these may be, gain
their instant acceptance and applause. On the other hand whatever is
brought forward against it, however ingenious and conclusive, they
receive with disdain or with hot rage--if indeed it does not make them
ill " Galileo
I think anyone who goes outside and enjoys walking the countryside or the beach,spends a few moments taking in the spectacle of the celestial arena does feel a sense of the immensity of age and scale of things without straining the mind for we too are part of the evolution of life on Earth as an individual,as a community,a nation,a species,within the wider context of biological and geological evolution,planetary evolution,solar system evolution and on to greater cycles so the individual is never cut off from the Universal but encompassed by it.More than anything else,what strains the mind unnaturally about the idea of 'big bang' is that we can see the evolutionary timeline of the Universe directly and this way of thinking cuts us off from the connections we have with the evolutionary past and while the impossible concept may appear to be a product of superior intellect,it has no soul to it and exists only in the imagination.0 -
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Cú Giobach wrote: »Check out the "Michelson-Morley experiment", This was one of the biggest ever discoveries in physics, the consequences of which Einstein later dealt with in his theories of relativity.
Who wrote this and why is it important to your statement above ? -
"The fictitious matter which is imagined as filling the whole of space
is of no use for explaining the phenomena of Nature, since the motions
of the planets and comets are better explained without it, by means of
gravity; and it has never yet been explained how this matter accounts
for gravity. The only thing which matter of this sort could do, would
be to interfere with and slow down the motions of those large
celestial bodies, and weaken the order of Nature; and in the
microscopic pores of bodies, it would put a stop to the vibrations of
their parts which their heat and all their active force consists in.
Further, since matter of this sort is not only completely useless, but
would actually interfere with the operations of Nature, and
weaken them, there is no solid reason why we should believe in any
such matter at all. Consequently, it is to be utterly rejected."0 -
About what?Well, someone has to discover the 'next big thing'. Why not gkell? Or you for that matter.
All he does is tell everyone they are wrong, in a complicated, rambling and incoherent fashion but never explains about what or why, nor offers any alternative explanations or theories about these ethereal wrongs.0 -
Cú Giobach wrote: »About what?
All he does is tell everyone they are wrong, in a complicated, rambling and incoherent fashion but never explains about what or why, nor offers any alternative explanations or theories about these ethereal wrongs.
The passage I quoted was written by Newton in Optiks ,1704 where Isaac rejects an aether so you get to explain to Wh1stler why Michelson-Morley is one of the most important experiments in science without Newton's absolute/relative space and motion being a factor.
Btw,I spend most of my time promoting the original works of astronomers which effectively is an impossible task as it is so large and covers such a long time span yet all the online tools make is a labor of love and will be for anyone who decides to take these things on themselves. I am as much praising our era apart from the indifference or laziness in putting the new approach to astronomy to better use yet there are obstacles to this new approach and that means getting rid of unwanted things or conceptions that have long since outgrown their usefulness.If you wish to come to an understanding of what Isaac Newton was actually doing with absolute/relative space and motion,you only need to become more familiar with Kepler's representation and match it with contemporary imaging ,the idea being that we are moving in a conclusive direction instead of arguing in circles.0 -
Because we observe it as a form of time dilation. Can i rephrase your question like this:
"how can increasing distance from a receeding repeating source affect the wavelength of a sound if it has no affect on the sound. If time and distance cannot be experienced by a sound how can increasing distance from a receeding repeating source affect the wavelength. Doppler effect is this time dilation. And it is relativistic.
I wanted to use a sound analogy in the first place but expected that I would be lambasted for it.
To make the analogy a better fit, let's suppose that the sound source and the detector are stationary. And in order to factor in 'expansion', let's say that the air temperature at the source is cool and that the temperature increases along a gradient such that the air is warmest in the viscinity of the detector. This means that as the sound wave propogates, it passes through air which is decreasing in density at a constant rate.
So, when the sound wave leaves the emitter it travels at a speed that is only dependent on the density of the air. There is no Doppler effect, no time-dilation as source and detector do not alter their positions with respect to each other.
Now, if we were to make a recording of the sound that is emitted and a seperate recording at the detector and then compared the two recordings, wouldn't we hear a difference between the two? Wouldn't the sound wave lose actual energy through the change in air density? And isn't this equivalent to increasing wavelength of photons?0 -
You mean scientists have no real advantage over other scientifically literate humans of course unless you factor in budgets and scientific equipment. For eg. the scientists (particle physicists) at cern have a significant advantage over Irish scientists (irish particle physicists) in the field of particle research because Ireland is not a contributing member of Cern. As will future generations have an advantage over us. they will have had the benefit of more experiments and more results if they continue the scientific method with which to draw conclusions from.
What I meant was that even a lowly clerk in a patent office can come up with a good idea from time to time.0 -
Cú Giobach wrote: »Since Slade_x dealt with your other points, I'll only deal with this one.
The speed of light is constant, irrespective of the motion of the emitter, and is always measured the same, irrespective of the motion of the observer.
For example, if you were on a spaceship travelling at 10,000 km/s and you shone a beam of light in your direction of travel, the beam would not be travelling at 310,000 km/s, but still at c ie; 300,000 km/s.
And if you were travelling towards a beam of light on a spaceship at 10,000 km/s, you would still measure the speed of the beam as 300,000 km/s.
Check out the "Michelson-Morley experiment", This was one of the biggest ever discoveries in physics, the consequences of which Einstein later dealt with in his theories of relativity.
But I was talking about relative velocity.
A photon emitted from a space-ship that is travelling at 10,000 km/s and in the same direction would move away from the space-ship at 290,000 km/s, wouldn't it? And if the photon was travelling in the opposite direction, the distance between photon and space-ship would increase by 310,000 km/s.0 -
But I was talking about relative velocity.
A photon emitted from a space-ship that is travelling at 10,000 km/s and in the same direction would move away from the space-ship at 290,000 km/s, wouldn't it? And if the photon was travelling in the opposite direction, the distance between photon and space-ship would increase by 310,000 km/s.
My understanding is no. Even if the spaceship was moving at 299,000 km/s, the photon would still move away from the spaceship at 300,000 km/s, rather than 1,000 km/s. Nor would the photon travel at 299,000 km/s + 300,000 km/s. At all times it would travel at 300,000 km/s as observed by all observers, everywhere, regardless of the velocity of the observer.0 -
A photon emitted from and in the same direction as a space ship travelling at 10,000 km/s will leave that ship at 300,000 km/s as measured by someone on the ship, an independent observer would also see the light moving at 300,000 km/sec.But I was talking about relative velocity.
A photon emitted from a space-ship that is travelling at 10,000 km/s and in the same direction would move away from the space-ship at 290,000 km/s, wouldn't it? And if the photon was travelling in the opposite direction, the distance between photon and space-ship would increase by 310,000 km/s.
An independent observer watching a spaceship travelling at 10,000 km/s in the opposite direction to a beam of light, would see the distance increase by 310,000 km/s, but to someone on the spaceship the beam would be travelling away from him at 300,000 km/sec, and to the independent observer the light would be travelling at 300,000 km/sec.
Even if a spaceship is travelling at 229,000 km/s and measures the speed of an approaching beam of light, it will measure the speed as 300,000 km/s, the beam of light will not be hitting the detector at almost twice the speed of light. In other words, "the relative speed between photon and detector is constant, irrespective of the speed of the detector".
Time is not fixed and there is no "absolute" time to measure things with respect to, velocity is distance/time, time is relative to an observer, keeping the velocity at c irrespective of motion (not to mention the change in the size of your ruler as your velocity changes).0 -
Cú Giobach wrote: »A photon emitted from and in the same direction as a space ship travelling at 10,000 km/s will leave that ship at 300,000 km/s as measured by someone on the ship, an independent observer would also see the light moving at 300,000 km/sec.
An independent observer watching a spaceship travelling at 10,000 km/s in the opposite direction to a beam of light, would see the distance increase by 310,000 km/s, but to someone on the spaceship the beam would be travelling away from him at 300,000 km/sec, and to the independent observer the light would be travelling at 300,000 km/sec.
Even if a spaceship is travelling at 229,000 km/s and measures the speed of an approaching beam of light, it will measure the speed as 300,000 km/s, the beam of light will not be hitting the detector at almost twice the speed of light. In other words, "the relative speed between photon and detector is constant, irrespective of the speed of the detector".
Time is not fixed and there is no "absolute" time to measure things with respect to, velocity is distance/time, time is relative to an observer, keeping the velocity at c irrespective of motion (not to mention the change in the size of your ruler as your velocity changes).
Suppose the space-ship was travelling towards me at the speed of light and sent a beam of light towards me at the same time; which would arrive first, the ship or the beam of light?0 -
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Cú Giobach wrote: »Time is not fixed and there is no "absolute" time to measure things with respect to, velocity is distance/time, time is relative to an observer, keeping the velocity at c irrespective of motion (not to mention the change in the size of your ruler as your velocity changes).
Let's see where you are getting this statement from -
"Absolute time, in astronomy, is distinguished from relative, by the
equation or correlation of the vulgar time. For the natural days are
truly unequal, though they are commonly considered as equal and used
for a measure of time; astronomers correct this inequality for their
more accurate deducing of the celestial motions... The necessity of which
equation, for determining the times of a phænomenon, is evinced as well
from the experiments of the pendulum clock, as by eclipses of the satellites
of Jupiter." Isaac Newton,Principia
The Equation of Time is a tricky one,it represents the conversion of natural noon cycles into 24 hour clock cycles.It is not a matter of running around declaring there is no absolute time or there is only relative time,it fundamentally represents the difference in formats between the Lat/Long system where 15 degrees represents 1 hour time difference and the Ra/Dec system which uses the average 24 hour day and the 365/366 day calendar format in tandem with stellar circumpolar motion.
The reference by Newton to "the experiments of the pendulum clock, as by eclipses of the satellites of Jupiter " leaves the door open for observers to comprehend the role the 'fixed stars' play in clarifying what he was actually doing rather than the convenient story they made up in the early 20th century using absolute/relative space,motion and time.
Astronomers like Copernicus and Kepler didn't need clocks to come to their insights,they gauged the motion of the planets against the 'fixed stars' night after night just as observers here have witnessed lately how the combined motions of the Earth and Venus have moved the slower moving Jupiter from left to right of Venus or that Mars is moving backwards against the fixed stars -
http://apod.nasa.gov/apod/ap080511.html
When clocks appeared in the 17th century and especially the creation of the equatorial coordinate system by Flamsteed,the 'fixed stars' or what is today the 'inertial reference frame' relied on the daily stellar circumpolar motion -
http://www.youtube.com/watch?v=BYy0EQBnqHI
Instead of the planets moving against the stellar background as the older astronomers knew it,with Ra/Dec,everything moves with a rotating celestial sphere,some faster than others hence the convenience of predicting lunar and solar eclipses as days and dates within the calendar system,unfortunately it swamps the ability to conceive the orbital motion of the Earth along with the other planets and why many come here to ask about conjunctions or retrogrades when these line of sight observations should be familiar to students and adults alike.
The topic is so sprawling that it is much better for readers to approach astronomical timekeeping at the level they are most comfortable with and they can be assured that few among the well known investigators of the early 20th century even came close to understanding what Newton was trying to do -
"This absolute time can be measured by comparison with no motion; it
has therefore neither a practical nor a scientific value; and no one
is justified in saying that he knows aught about it. It is an idle
metaphysical conception." Mach, Analyse der Empfindungen, 6th ed.
The Lat/Long system determines that there is no external reference for daily rotation through 360 degrees while the Ra/Dec system concludes that there is and it is at this juncture where Mach and many today are still lost in the conceptual labyrinth Newton constructed on absolute/relative time.0
https://www.youtube.com/watch?v=PlH5X-YhdkE
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