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Author Topic:   Astronomers See Evidence of Something Unexpected in the Universe
Taq
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Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 56 of 86 (829778)
03-13-2018 4:38 PM
Reply to: Message 54 by nwr
03-12-2018 1:09 PM


nwr writes:
I have already attempted to explain -- without success.
There's no point in trying again.
I enjoy talking about theoretical physics and cosmology, so I will give it another try.
In your first post in the thread you talked about not having a yardstick that can be used through the entire cosmos. Cosmologists do think they have a common yardstick, or more precisely a standard candle.
The concept is this. If you stand 1 foot away from a candle it will have a certain measured brightness or luminosity. If you move 10 feet away its luminosity drops, and it keeps dropping at a specific rate over distance. If you use the same candle or a standard candle, you can always measure distance by measuring the luminosity.
The standard candles in cosmology are type Ia supernovae and Cepheid variables.
"It is possible to estimate the distance to a Cepheid in a far-off galaxy as follows: firstly, locate the Cepheid variable in the galaxy, then measure the variation in its brightness over a given period of time. From this you can calculate its period of variability. You can then use the luminosity-period graph (below) to estimate the average luminosity. Finally, armed with the average luminosity, the average brightness and using the inverse square law, you can estimate the distance to the star."
ESA Science & Technology - Stellar Distances
"When the white dwarf reaches 1.4 solar masses, or about 40 percent more massive than our Sun, a nuclear chain reaction occurs, causing the white dwarf to explode. The resulting light is 5 billion times brighter than the Sun.
Because the chain reaction always happens in the same way, and at the same mass, the brightness of these Type Ia supernovae are also always the same. The explosion point is known as the Chandrasekhar limit, after Subrahmanyan Chandrasekhar, the astronomer who discovered it.
To find the distance to the galaxy that contains the supernova, scientists just have to compare how bright they know the explosion should be with how bright the explosion appears. Using the inverse square law, they can compute the distance to the supernova and thus to the supernova's home galaxy."
Science
Do you have any objections to using these standard candles to measure distances to distant galaxies?

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 Message 54 by nwr, posted 03-12-2018 1:09 PM nwr has replied

Replies to this message:
 Message 57 by nwr, posted 03-14-2018 11:36 AM Taq has replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 58 of 86 (829797)
03-14-2018 12:47 PM
Reply to: Message 57 by nwr
03-14-2018 11:36 AM


nwr writes:
No objection at all. However, they do not get at the point I was raising.
Since we have agreement on the yardstick for measuring distances, let's also discuss how redshift is measured and see if the point you are trying to get across has any impact on these measurements.
Over at the SDSS server you can get the actual spectra for galaxies.
http://skyserver.sdss.org/dr14/en/get/SpecById.ashx?id=43...
I'm kind of a nut for liking to look at raw data, but I think it illustrates a point. Those are the adsorption and emission lines for different elements in those galaxies, and they can measure their wavelength. They can then compare those wavelengths to what they are in a stationary frame of reference. As it turns out, these emission and absorption lines are shifted towards lower wavelengths, and that shift is expressed as a z value. Not only that, but the change in wavelength is the same for all wavelengths which is why it is called a wavelength independent redshift. Mechanisms that directly interact with light will do so in a wavelength dependent manner, meaning that different wavelengths will be more strongly redshifted than others. The only known mechanism that produces a wavelength independent redshift is a difference in velocity between two objects.
When you plot distance v. z value you get an extremely strong correlation. Cosmologists interpret this as all galaxies moving away from our galaxy in a distance dependent manner. The only thing that makes sense of these observations is that all space is expanding equally in all directions, everywhere.
Is there something you object to in these measurements of redshift and distance, or the conclusions drawn from them?
Edited by Taq, : No reason given.

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 Message 57 by nwr, posted 03-14-2018 11:36 AM nwr has replied

Replies to this message:
 Message 60 by nwr, posted 03-15-2018 11:32 AM Taq has replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 61 of 86 (829859)
03-15-2018 2:57 PM
Reply to: Message 60 by nwr
03-15-2018 11:32 AM


nwr writes:
That's what I am questioning.
So what mechanisms are you pointing to that could create this wavelength independent redshift that appears to increase with distance from the Milky Way? Why do you see expansion as a questionable conclusion?
A second check on the conclusion of space expansion is the CMB. If you run the expansion backwards you would predict that all matter would have been crammed into a very small space, and would have been really, really hot. Initially, this matter would be a plasma and would be opaque to EM radiation. Some time later, as the matter expanded and cooled, would you get atomic hydrogen which does allow EM radiation to move freely in the universe. That prediction was confirmed in the form of the CMB which is EM radiation that is coming from everywhere in the universe.

This message is a reply to:
 Message 60 by nwr, posted 03-15-2018 11:32 AM nwr has replied

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 Message 62 by nwr, posted 03-15-2018 4:09 PM Taq has replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


(1)
Message 63 of 86 (829864)
03-15-2018 4:14 PM
Reply to: Message 62 by nwr
03-15-2018 4:09 PM


nwr writes:
I am suggesting that conclusions about expansion are premature. We do not know nearly enough to jump to such conclusions.
Would you agree that all of the observations we have thus far are consistent with expansion?

This message is a reply to:
 Message 62 by nwr, posted 03-15-2018 4:09 PM nwr has replied

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 Message 65 by nwr, posted 03-17-2018 4:00 PM Taq has not replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 64 of 86 (829891)
03-16-2018 11:00 AM


Independent Lines of Evidence
nwr finds the evidence for expansion to be inadequate, so I thought I would at least discuss why I think it is adequate to draw a scientific conclusion (i.e. a tentative conclusion).
One of the hallmarks of a well supported theory in science is the consilience of multiple lines of evidence. It is always a bad idea in science to draw strong conclusions from a single experiment, or even a single type of experiment. Most recently, the Higgs boson was discovered at CERN, and this discovery was made by two separate and isolated labs using two different instruments. The fact that their conclusions agreed with one another only further strengthened their conclusions.
So what are the independent lines of evidence for the Big Bang and the continued expansion of space? There are at least 3:
1. The correlation between redshift and distance.
2. The cosmic microwave background.
3. The ratio of light elements.
The third piece of evidence has to do with the expected ratios of hydrogen, helium, and lithium in the universe. If the universe started out as a really hot and dense ball of matter and energy then we would expect to see about a 3 to 1 ratio of hydrogen to helium with all other elements making up about 2% of the total which is exactly what we see, as discussed here.
So we have three completely independent lines of evidence, all of which match the predictions made by the Big Bang theory which includes continued expansion of the universe. This is why I agree that the Big Bang model deserves to be accepted as tentatively true. I think it has passed the tests needed to gain consensus within astrophysics.
I would be interested in hearing why people think that these independent lines of evidence are inadequate.
Edited by Taq, : No reason given.

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 Message 66 by nwr, posted 03-17-2018 4:34 PM Taq has replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 77 of 86 (829973)
03-19-2018 11:35 AM
Reply to: Message 66 by nwr
03-17-2018 4:34 PM


Re: Independent Lines of Evidence
nwr writes:
If you take red-shifted light, and red-shift it even more, you get microwave radiation. So I don't see that as independent evidence.
There is also the fact that it is coming from everywhere in the universe and that it has the predicted power spectrum.

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Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 78 of 86 (829974)
03-19-2018 11:38 AM
Reply to: Message 68 by nwr
03-17-2018 4:56 PM


nwr writes:
So better to call it an hypothesis, rather than a theory.
Then I would be curious as to what you think a scientific theory is. In my view and the view of the vast majority of scientists, a scientific theory is a set of tested and supported hypotheses. The redshift of galaxies, the CMB, and the ratio of light elements tested those hypotheses and they were supported. Therefore, scientists call it the Big Bang theory.

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Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 79 of 86 (829975)
03-19-2018 11:39 AM
Reply to: Message 72 by nwr
03-18-2018 12:23 AM


nwr writes:
It would have been better if I had used "convincingly".
Then it just comes down to how stubbornly you will hold onto a position.

This message is a reply to:
 Message 72 by nwr, posted 03-18-2018 12:23 AM nwr has replied

Replies to this message:
 Message 84 by nwr, posted 03-20-2018 6:26 PM Taq has replied

  
Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 80 of 86 (829976)
03-19-2018 11:44 AM
Reply to: Message 71 by nwr
03-18-2018 12:20 AM


nwr writes:
A theory should establish standards for research in the area. The Hubble red shift did that, by providing a new standard for measuring distance to remote galaxies. I'm not seeing anything comparable with BB.
A standard of measurement is not a theory.
Also, the BB theory predicts that redshift will correlate with distance. For most of us, when predictions made by a hypothesis match observations we call that a supported hypothesis. A theory is a group of supported hypotheses and is also a framework or model for making further hypotheses. That's the standard in science.
quote:
The term nucleosynthesis refers to the formation of heavier elements, atomic nuclei with many protons and neutrons, from the fusion of lighter elements. The Big Bang theory predicts that the early universe was a very hot place. One second after the Big Bang, the temperature of the universe was roughly 10 billion degrees and was filled with a sea of neutrons, protons, electrons, anti-electrons (positrons), photons and neutrinos. As the universe cooled, the neutrons either decayed into protons and electrons or combined with protons to make deuterium (an isotope of hydrogen). During the first three minutes of the universe, most of the deuterium combined to make helium. Trace amounts of lithium were also produced at this time. This process of light element formation in the early universe is called Big Bang nucleosynthesis (BBN).
The predicted abundance of deuterium, helium and lithium depends on the density of ordinary matter in the early universe, as shown in the figure at left. These results indicate that the yield of helium is relatively insensitive to the abundance of ordinary matter, above a certain threshold. We generically expect about 24% of the ordinary matter in the universe to be helium produced in the Big Bang. This is in very good agreement with observations and is another major triumph for the Big Bang theory.
WMAP Big Bang Elements Test

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Taq
Member
Posts: 9973
Joined: 03-06-2009
Member Rating: 5.6


Message 85 of 86 (830091)
03-21-2018 11:59 AM
Reply to: Message 84 by nwr
03-20-2018 6:26 PM


nwr writes:
Clearly wrong. I am not holding onto a position. I am patiently waiting to see what other evidence shows up.
Until you explain why at least 3 independent lines of evidence are not enough it looks a lot like stubbornness.

This message is a reply to:
 Message 84 by nwr, posted 03-20-2018 6:26 PM nwr has seen this message but not replied

  
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