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cmancone
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Posted: Thu Oct 19th, 2006 07:16 pm |
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On your webpage, you have a lot to say about astronomy units and graphing. For instance, you attempt to debunk the CMB curve on the basis of this:
BUT, wait a minute, that wavelength scale looks a bit funny. Lets look at the divisions, 1, 0.2, 0.1, 0.07 don't they seem a little strange? A typical blackbody curve has intensity plotted against wavelength - with a linear scale. I mean, if it is an intensity/frequency diagram then why not put the frequency scale at the bottom? Why put wavelength at the bottom of your graph, with a strange non linear scale to boot, if you are plotting against frequency?
You should realize that astronomers don't use the same standard units of the rest of science. The simple fact of the matter is, there is nothing wrong with this. Astronomy is a lot different that typical physics. In astronomy, a meter is a pretty worthless unit for distance. A kilogram isn't much better. For this reasons and for historical concerns (astronomy has been around much, much longer than MKS units have), astronomers use a variety of different units. For instance, the standard units for astronomers are CGS (centimeters-grams-seconds). However, when you step out of the local neighborhoood, astronomers use a completely different set of units. For mass, we use Solar Masses. For distances, we use parsecs. For brightnesses, we actually use magnitudes. The point is, units are completely arbitrary. Astronomers can use whatever they want and it doesn't matter, as long as they are understood. This is always the case. The only important thing to remember is to mention what units are being used. This is important, and it is always done. I note, for instance, that in the CMB plot you included from NASA's website the units of the x and the y axis were labeled. I also notice, however, that the plots of black body spectra you included don't have units. This is very bad. Let me speak briefly about graphing and an amazining new notion: logarithmic plots
Astronomers often plot things in logarithmic space. What this means is that instead of plotting the x and y values of a data set, astronomers plot the logarithm of the x and y values. Or, sometimes, they plot the values themselves but make the scale of the x and y axis logarithmic. In this case, the scale of the axis will not have standard linear scaling. This is almost certainly the case with the plot you have included in your website. There is a number of advantages to logarithmic scaling, which is why it is commonly used. First of all, it is often used when a dataset spans a large range. Check out the plots I've made below. The first plot is a simple y=x^2 data set, which varies over a large range of values. You can see that because of the large range, it's hard to tell what is going on near the origin.
http://conor.manconefamily.com/plots/linscl.png
Now, let's replot the exact same data on a logarithmic scale:
http://conor.manconefamily.com/plots/logscl.png
It's obvious that this evens things out quite nicely. It makes it easier to see what's going on. Also, these plots demonstrate another advantage of logarithmic scales. Namely, power laws are very easily identified in a logarithmic scale. When I plotted the y=x^2 data in log-log space, the curve turned into a straight line with a slope of 2. If I had plotted a y=x^3 curve in log-log space, I would have gotten another straight line, with a slope of 3 this time. Exponential functions, however, are still curves in log-log space. For instance, here is a plot of e^x in linear space:
http://conor.manconefamily.com/plots/ex.png
and here's the same plot in log-log space
http://conor.manconefamily.com/plots/logex.png
You can see that exponentials in log space are still curves, but change in shape. In the case of the CMB plots, log-log (or log-linear) space would likely be used because a black body curve covers a large range of wavelengths. That is why there is such a "strange" scale. At the same time, the plots of black body diagrams you provided would have also been in log-log space. However, that can't be verified because the plots you chose don't have any information on units or how they were plotted. They were almost certainly plotted in log-log space though. That's why when you re-plotted the measured CMB curve in liner space it no longer matched - because the curves you were comparing it to were in log space themselves.
However, you don't have to take my word for it. On the Ned Wrights cosmology page that you provided a link to there is a plot of an actual black body curve with the FIRAS data plotted over it on the same scale!! If you were to simply look at this graph, you would see that the data match perfectly, with no adjustments necessary. In fact, the data is even plotted with 400sigma error bars, just to make the error bars visilbe. Please note that the actuall value of a datapoint will lie within 3sigma over 99% of the time. To include 400sigma error bars is complete and total overkill, and was done simply because the 3sigma error bars wouldn't be visible.
You say:
Now, I am not in the least bit cynical (!), but someone who was might think that it was all a con. That is, trying to make us think that these 'intensity frequency' graphs are 'intensity wavelength' graphs. The graphs 'look' like the traditional blackbody curves only when they are drawn against frequency. What does the Firas data 'look' like when it is drawn in the 'blackbody' way of intensity against wavelength? Lets have a look:
You are mistaken. The graphs look exactly like black body curves when plotted on the same scale with the same units. The only time they look different is when you redraw the FIRAS data on a linear scale and expect it to look like a black body drawn on a logarithmic scale.
Next, you say:
What strange units for 'professional' scientists to use! km/s per Mpc. 'Mpc' means megaparsec and it is a unit of distance. But km is also a unit of distance so why have two different units for distance in the same expression? Why not Mpc/s per Mpc? Or km/s per km? Or even m/s per m? Ah! but wait a minute, if one has 'm/s per m', the metres cancel to give 'per sec' or just s-1 . But then it is not a velocity. people would never believe that the universe was expanding if the units were just 'per sec' and had no units of velocity in there, would they? Methinks the units of km/s per Mpc are a con to make people think that the universe is expanding. The proper unit for H is s-1. Lets use that instead.
As we have already discussed, astronomers use "strange" units because they work. Astronomers quote distances in parsecs because we measure parsecs. No one has ever measured cosmic distances in meters. Because of the basis of the distance scale all measurements are made in parsecs, and then converted to other units as desired by non-astronomers. However, astronomers can use whatever units they want. There is no such thing as "proper units" as you've tried to imply elsewhere in your site. As I said, astronomy has been around a lot longer than the MKS system.
Most importantly, astronomers list the Hubble Constant in units of km/s/Mpc because it is a more intuitive system of units. Since the universe is expaning, the hubble constant does indeed represent the speed of that expansion per unit of distance. As you yourself have said, Ho = 72km/s/Mpc means that two objects separated by one Mpc will be moving apart at 72km/s. Working in these units make for much more convenient numbers. It's easier to remember the Hubble constant being 72km/s/Mpc than it would be to remember that the hubble constant is 2.4x10^-18 meters/sec/meter. Because the universe is expanding (as verified from FIRAS measurements of the CMB), it is perfectly legitimate to understand the Hubble constant as an expansion speed per unit of distance. It is not done to confuse and fool people. At the same time, the Hubble Constant does have units of /s In fact, this is well understood by just about anyone who has taken an astronomy class, because one of the first things that is done with the hubble constant is inverting it to calculate the age of the universe (in seconds). Certainly there is no astronomical conspiracy to confuse people.
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lyndonashmore
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Posted: Fri Oct 20th, 2006 11:12 am |
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Hi Cmancone,
Astronomers often plot things in logarithmic space. What this means is that instead of plotting the x and y values of a data set, astronomers plot the logarithm of the x and y values. Or, sometimes, they plot the values themselves but make the scale of the x and y axis logarithmic. In this case, the scale of the axis will not have standard linear scaling. This is almost certainly the case with the plot you have included in your website. s is almost certainly the case with the plot you have included in your website
No,
they put wavelength at the top of the graph or they use waves per centimetre and not wavelength! The only reason for this is to deceive.
As for unts, as you say astronomers can use any unt they like provided they
1) state the unit
2) use a consistent set of units.
"km/s per Mpc" fails on the second count. Fine, if they want to use parsec as a unit of distance then let them use it - but don't put km in the units of the same quantity.
Use "parsec/sec per parsec" for the Hubble constant and no one would complain. But to set H out as "72km/s per Mpc" then they are trying to fool people into thinking that there is a velocity in there and an expanson - which there is definately not!
Cheers,
lyndon
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cmancone
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Posted: Fri Oct 20th, 2006 01:24 pm |
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I assure you, astronomers don't do this to decieve. If you are trying to imply that there is a vast conspiracy about the big bang in astronomy, I am afraid that you are mistaken. When astronomers make graphs they don't confuse other astronomers. If the original investigators into the big bang tried to fudge the units on their graphs to make things look right, it would be noticed, and no one would accept the results.
I noticed that you ignored my most important point. When plotted together on a graph with the same units and the same scales, the FIRAS data and a theoretical blackbody are an EXACT match. If astronomers were fudging the units of their graphs, this would not happen. Clearly then, you are wrong.
I told you why astronomers use units of km/s/Mpc. It really is to get out nice numbers. If this is not acceptable to you, then you are just S.O.L. It doesn't confuse astronomers, and it doesn't confuse most of the public either. If you have a problem with it, I'm afraid you're on your own.
Astronomers have been using crazy units for as long as they have been around. They have even made up their own systems of units to get nice numbers out of things. For instance, this isn't well known outside of specific fields in astronomy, but some astronomers use canonical units. In the system of canonical units, 1 "mass" is equal to about 282 solar masses. Speeds are measured in km/s, and lengths in parsecs. These units are defined to be these values because in this system of units the Gravitaional constant happens to come out to 1. It makes doing calculations in your head very easy. The fact that astronomers made up a system of units just to get nice numbers should show you that using units of km/s/Mpc to get a nice number is not in the least bit surprising. It's how astronomers work. Astronomers can't do their work in a more standard system of units, so they don't bother limiting themselves at all.
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lyndonashmore
Administrator
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Posted: Fri Oct 20th, 2006 01:51 pm |
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Hi Cmancone,
I told you why astronomers use units of km/s/Mpc. It really is to get out nice numbers. If this is not acceptable to you, then you are just S.O.L. It doesn't confuse astronomers, and it doesn't confuse most of the public either. If you have a problem with it, I'm afraid you're on your own.
But it does confuse both astronomers and the public! Because inserting two units that cancel (or would cancel if they were scientfic and used a consistent set of units) is there to confuse. it is there to trump up a velocity to get expansion.
"Km/s per Mpc" should be "Mega Parsec per sec per Mega Parsec" or "Km/sec per Km". And then everyone would say "Hang on a minute, the distance units cancel. It is really a Second to the minus one with no velocity anywhere"
Why else would they do it?
Cheers,
Lyndon
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cmancone
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Posted: Fri Oct 20th, 2006 02:28 pm |
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I'm not going to repeat myself anymore. They did it because:
1) The universe is expanding, so the hubble constant can be represented as a velocity/distance. This does have units of /s, because the expansion is a fractional expansion. This much space expands by this much. Fractions, however, are unitless. To be more specific, the units are not m/s/m, they are m/m/s. In other words each meter expands by this much per second. It is a fractional expansion, which is why the units of distance cancel out.
2) Astronomers use two different sets of units because they get nice numbers that way. That's it. That's the only reason. Your hypothesis that they do it to confuse people is ridiculous. In order for that to be true, every single astronomer would have to be in on it, because the fact that km/s/Mpc is in units of /s is obvious to every single astronomer, just like it's obvious to you. However, there is no vast astronomical conspiracy. In fact, when the big bang was proposed most astronomers rejected it because they didn't want to believe in a big bang. However, they stopped their opposition to it once it worked its way onto a firm theoretical ground. That's how science works. Astronomers are not taking part in some big consipiracy to make the Big Bang true, they would reject it if the evidence didn't fit.
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lyndonashmore
Administrator
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Posted: Sat Oct 21st, 2006 07:25 am |
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Hi Cmancone,
No it is a fiddle. There is no direct evidence to show expansion or a 'cosmologcal velocity'.
The only evidence we have is that photons from distant galaxies have a longer wavelength on arrival than when these same photons set off.
This is what is measured- a shift in wavelength. Anything other than this is an interpretation of the results - and in the case of 'expansion' a wrong one.
Ergo the unit 'km/s per Mpc is a con trick to make us believe that the unverse is expanding.
Cheers,
Lyndon
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cmancone
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Posted: Thu Oct 26th, 2006 03:40 pm |
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Redshifts are only introduced by one of two methods:
Method 1: The observer is moving away (i.e. has a velocity)
Method 2: Time dilation
When you notice that more distant objects have higher redshifts than closer ones, the first and foremost reason for this to happen is because the object is moving away from us (i.e. it is redshifted). Therefore, it is not suprising that the Hubble constant (which is a measure of redshift) is a measure of velocity. Redshift = velocity, Hubble Constant = velocity. This is why the Hubble constant is in units of speed/distance. It is also in units of /s. Both are correct.
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lyndonashmore
Administrator
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Posted: Sun Oct 29th, 2006 06:41 pm |
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No No No.
There are lots more ways to get redshift.
Leaving my own theory to one side for a nanosecond, there is
Gravitational redshift - proven in the laboratory,
The Wolf effect - proven in ther laboratory
Has stretching of space redshift been reproduced in the laboratory? - NO!
What we know is that redshift increases with distance - but age changes too. The light emitted from more distance galaxies was emmitted earlier in the life of the universe (in an expanding universe) so how do we know that the planck constant is not time dependent? Was it Arp who said that 'h' could be time dependent and decreasing with time. After all we have only been measuring 'h' for a hundred years or so and this is nothing compared with the age of the universe. How do we know that it is not time dependent? Light from galaxies further away was emmitted when the universe was younger and 'h' was perhaps greater at that time. 'h' is greater, so we have a smaller frequency for the same energy (E = hf). Smaller frequency means larger wavelength - redshifted!
However, photons from galaxies twice as far away having twice the redshift is best explained by these photons having travelled twice as far through the galactic medium. They have made twice the number of collisions, lost twice the energy, had their frequency reduced by twice as much and thus have had their wavelength increased by twice as much. Twice the redshift. Tired Light
You know it makes sense!
Cheers,
Lyndon
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cmancone
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Posted: Sun Oct 29th, 2006 06:51 pm |
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lol! Gravitational redshift = redshift from time dilation. The two are exactly the same as per general relativity.
The wolf effect is highly specific and doesn't apply in our current discussion. The light from most galaxies is not in the least bit coherent.
Of course redshift by stretching space hasn't been reproduced in the labratory - we can't stretch space. However, stretching space would clearly create a redshift. Just because we haven't reproduced it doesn't mean it hasn't happened.
However, photons from galaxies twice as far away having twice the redshift is best explained by these photons having travelled twice as far through the galactic medium. They have made twice the number of collisions, lost twice the energy, had their frequency reduced by twice as much and thus have had their wavelength increased by twice as much. Twice the redshift. Tired Light
You know it makes sense!
 Honestly, it doesn't make sense. There's a lot wrong with it. But that's why I'm here.
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lyndonashmore
Administrator
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Posted: Mon Oct 30th, 2006 01:24 pm |
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Ah! But does it?
One gets the same results as those said to be due to GR if one uses Newtonian mechanics. The total energy of the photon is 'mgh' + hf and as 'mgh' ncreases, hf reduces and so lambda increases - redshift!
Cheers,
lyndon
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