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 Post subject: Re: James Web Telescope
PostPosted: 06 Aug 2022, 12:03 
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It will do a better job than existing telescopes of seeing gravitational leasing from dark matter. (which has already been seen by other telescopes). There are places like the bullet galaxy https://en.wikipedia.org/wiki/Bullet_Galaxy where the gravitational field is not coming from where the visible matter is - a strong hit at the existence of dark matter.

Dark energy is more difficult because its everywhere. Different types of telescopes that do very broad sky surveys are better for that. https://www.lsst.org/ (I helped design a tiny, inconsequential, boring bit of that one, but my lab (SLAC) did a lot of the project)


Other telescopes like https://simonsobservatory.org/ are looking for cosmological inflation, which is similar to dark energy, but happened very early in the universe.


Username Protected wrote:
For years we have been reading and hearing of "dark matter" and "dark energy". I'd like to know if the JW telescope has shown any of that dark matter.


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 Post subject: Re: James Web Telescope
PostPosted: 06 Aug 2022, 12:07 
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Username Protected wrote:
“Dark Matter” is a fancy name for “we don’t understand it”. Humans detest mysteries and so quickly make up “answers” to the ones they encounter. Theologians call it “God”, climate scientists call it “adjusting the model”, astrophysicists have adopted “dark matter”.

I don’t like the idea because it tends to suggest an answer when we really have no idea, and so risks missing the truth in favor of a fabrication that validates our expectation. I’d rather just say “we don’t know” and let the science take us to the answer.

I thought dark matter is what I saw earlier this morning when I dropped the kids off at the pool.


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 Post subject: Re: James Web Telescope
PostPosted: 06 Aug 2022, 16:10 
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Its really not.

We know a lot about dark matter, we just don't know what it "is".

We know it has mass and that mass has gravitational effects. We know it not made up of protons, neutrons, electrons, neutrinos, or their anti-particles. We know it doesn't decay at any significant rate. We know its interaction with the the strong or electro-weak forces is extremely small, maybe zero. We know it is relatively cold. We know how much of it there is and have a pretty good idea of how it is distributed.

A lot of experiments are ongoing to detect it expermentally, but that may not be possible if it only couples gravitationally, that would leave indirect measurements as the only way to locate it. (the gravitational interaction would be too weak for any imaginable laboratory experiment).

There are things we don't know, the biggest is the mass of dark matter particles. There is an enormous range of possible masses that fit the data we have so far.





Username Protected wrote:
“Dark Matter” is a fancy name for “we don’t understand it”. Humans detest mysteries and so quickly make up “answers” to the ones they encounter. Theologians call it “God”, climate scientists call it “adjusting the model”, astrophysicists have adopted “dark matter”.

I don’t like the idea because it tends to suggest an answer when we really have no idea, and so risks missing the truth in favor of a fabrication that validates our expectation. I’d rather just say “we don’t know” and let the science take us to the answer.


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 Post subject: Re: James Web Telescope
PostPosted: 06 Aug 2022, 17:50 
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Username Protected wrote:
I’d rather just say “we don’t know” and let the science take us to the answer.

Postulating the existing of dark matter is science in action. Observe the phenomenon, theorize a possible explanation, find ways to test the theory.

There is no path from observation to fact without going through theory.

One could argue there are no facts, only theories which vary in reliability. Newtonian gravity appeared to be fact, explained the universe as we understood it until the late 19th century, then Einstein showed it wasn't entirely correct, for example. Dark matter may yet show Einstein's theory isn't entirely correct, either.

Mike C.

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 Post subject: Re: James Web Telescope
PostPosted: 06 Aug 2022, 23:58 
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Username Protected wrote:
“ Humans detest mysteries and so quickly make up “answers” to the ones they encounter.


It’s worse then that John, we make up everything, we love stories. It’s what separates us for all other life on Earth. We make up rules and regulations to live by, none of them actually exist…

Anyway back to topic!

Andrew


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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 04:43 
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I’m standing underneath the stars tonight, without a telescope. I still feel really small.
For the dog days of summer, this is a beautiful night.


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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 10:56 
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I’m standing underneath the stars tonight, without a telescope. I still feel really small.

On a typical summer day in your area or mine, you look up and see lots of stars.

Now go to Mauna Kea visitor center at night and look up. You will be blown away by the number of stars, easily a thousand times more than you have seen before. There is almost no black between them. The stars, on a moonless night, are so bright you can easily see around you.

A part of the Milky Way from Mauna Kea (click on it to get full resolution):
Attachment:
milky-way-mauna-kea.png

It is a life changing experience to see that many stars with your unaided eyes.

Mike C.


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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 11:25 
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Username Protected wrote:
… You will be blown away by the number of stars, easily a thousand times more than you have seen before. There is almost no black between them.

And, based on what we are seeing from JWST, it seems that most of the “stars” you can see are more likely “galaxies”. The universe is indeed a big place.

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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 11:55 
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Mike,
I remember you previously posting about your star gazing experience at Mauna Kea. Yes, I’m envious. I purposely do not have a yard light. I’m over a mile from the nearest residence with a yard light. It’s not anywhere near as good as I’d like, but it’s still an epic sky for this hillbilly.


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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 12:04 
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It is big, but what you see are stars and planets. The galaxies are too faint for the naked eye (shows just how much better telescopes are than eyes).

Andromeda is supposed to be naked-eye visible in dark skies, but just barely and I've never seen it. The magellenic clouds are visible in the southern hemisphere, but I think those are the only extra-galactic objects you can see with your naked eye


Username Protected wrote:
… You will be blown away by the number of stars, easily a thousand times more than you have seen before. There is almost no black between them.

And, based on what we are seeing from JWST, it seems that most of the “stars” you can see are more likely “galaxies”. The universe is indeed a big place.


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 Post subject: Re: James Web Telescope
PostPosted: 07 Aug 2022, 14:38 
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we recently returned from Spanish Cay (mentioned in the Bahamas thread).

each night we stopped on the way to our hotel room, and could see the milky-way. it looked like a streak of cloud stretching across the sky.

and the amount of rum we had; there was no shortage of philosophizing...

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 Post subject: Re: James Web Telescope
PostPosted: 08 Aug 2022, 00:09 
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Username Protected wrote:
Andromeda is supposed to be naked-eye visible in dark skies, but just barely and I've never seen it.

On my Mauna Kea visit, we did see Andromeda, one of the few galaxies visible to the naked eye. It was quite clearly visible.

A pair of binoculars allowed you to see it wasn't a single point of light, though it sort of looked "smudged" to the naked eye before that.

A 24 inch telescope they had setup gave you a gorgeous picture of a spiral galaxy.

2.5 million light years away. Humans did not exist when the light I saw was generated. It would take 5 million years to ask someone in Andromeda a question and get an answer back, and this is a galaxy that is VERY close to us relatively speaking.

Mike C.

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 Post subject: Re: James Web Telescope
PostPosted: 08 Aug 2022, 07:16 
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Username Protected wrote:
I’d rather just say “we don’t know” and let the science take us to the answer.

Postulating the existing of dark matter is science in action. Observe the phenomenon, theorize a possible explanation, find ways to test the theory.

There is no path from observation to fact without going through theory.

One could argue there are no facts, only theories which vary in reliability. Newtonian gravity appeared to be fact, explained the universe as we understood it until the late 19th century, then Einstein showed it wasn't entirely correct, for example. Dark matter may yet show Einstein's theory isn't entirely correct, either.

Mike C.

Mike, I'd guess that John has no fault with the Scientific Process, but rather with the term Dark Matter.

We have a phenomenon, i.e., the rate of rotation of the outer portions of galaxies, that appears to require more gravity than we assign to the galaxies to conform to our laws of angular momentum and gravity.

But it's been pointed out by, I believe, Sabine Hossenfelder et al. that to call this missing attractive force dark "matter"--implying that it's the result of something made of bosons, i.e., some sort of matter, is presently unjustified by the facts.

All we really know at this point is that there appears be "something" that interacts with regular matter only gravitationally (as best we can determine). But to call this something "matter" (probably just a placeholder) may confuse the issue, at least for the layman.

It may be, as you point out, evidence of our incomplete knowledge of gravity, or it may well be something else.

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 Post subject: Re: James Web Telescope
PostPosted: 08 Aug 2022, 08:35 
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Here's an interesting podcast (365 Days of Astronomy) episode about dark matter and dark energy.

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 Post subject: Re: James Web Telescope
PostPosted: 08 Aug 2022, 12:44 
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If all we had was galaxy rotation data, that would be a reasonable description, but astrophysics progresses rapidly. We have things like the bullet galaxy where the center of gravitational lensing is not in the same place as the visible matter due to a galaxy collision.

From cosmology measurements, there are also pretty detailed fits to the amount of mass in the universe, and that disagrees strongly with the known amount of baryonic matter ( normal stuff) as measured by big bang nucleosynthesis. (if there were more baryonic matter, there would be more helium and heavier elements in the universe).

The problem is that in modern science, the measurements are pretty complex and it takes a lot of background to see how they relate to the things being measured. So unless someone is in the field, its not at all apparent on how statistics on the density of galaxies is realted to the amount of mass density in the universe. (I was involved in instrument design, but I don't understand the phenomenology)

Username Protected wrote:
Mike, I'd guess that John has no fault with the Scientific Process, but rather with the term Dark Matter.

We have a phenomenon, i.e., the rate of rotation of the outer portions of galaxies, that appears to require more gravity than we assign to the galaxies to conform to our laws of angular momentum and gravity.

But it's been pointed out by, I believe, Sabine Hossenfelder et al. that to call this missing attractive force dark "matter"--implying that it's the result of something made of bosons, i.e., some sort of matter, is presently unjustified by the facts.

All we really know at this point is that there appears be "something" that interacts with regular matter only gravitationally (as best we can determine). But to call this something "matter" (probably just a placeholder) may confuse the issue, at least for the layman.

It may be, as you point out, evidence of our incomplete knowledge of gravity, or it may well be something else.


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