James Webb Telescope

[Steve]

Let's try this again. The CMB is the reason we cannot see further back in time than about 13.6 billion years back or 13.6 billion years away. It does blot out everything, but not in the way I described. And yes, a better description is the universe would have been more of an opaque orange. According to some of the latest hypotheses the CMB would have made the universe too hot for subatomic particles to combine to make hydrogen which is needed to make stars.

I find this hypothesis strange since stars are far hotter. Time to revisit the physics.

There was a time when the early universe was far, far hotter than any star. And there was a time when it was far too hot for the atoms that make up elements to exist. Hydrogen is not created in stars. These are not hypotheses and none of this is the least bit controversial. Perhaps you are just not explaining well where you see a problem?

 

[acbytesla]

There was a time when the early universe was far, far hotter than any star. And there was a time when it was far too hot for the atoms that make up elements to exist. Hydrogen is not created in stars. These are not hypotheses and none of this is the least bit controversial. Perhaps you are just not explaining well where you see a problem?

My impression was that it was too hot to combine into elements like helium or hydrogen but that it is was colder than say temperatures in the corona of a star. But maybe I misunderstood. I've been watching astronomy videos almost non-stop since JWST was launched.

Time to watch some more.

 

[RecoveringYuppy]

And yes, a better description is the universe would have been more of an opaque orange.

Like the surface of some stars.

According to some of the latest hypotheses the CMB would have made the universe too hot for subatomic particles to combine to make hydrogen which is needed to make stars.

Comparable to the surface of a star. It's a plasma and we wouldn't be talking exotic subatomic particles at this time. It would be ordinary protons (hydrogen nuclei), alpha particles (helium nuclei), and electrons. Very much similar to the stuff on the surface of the Sun.

I find this hypothesis strange since stars are far hotter. Time to revisit the physics.

The temperature at the time of the origin of the CMB is comparable to the surfaces of stars for the same reason. The surface of the star is the point where the star becomes transparent to light. The time of the CMB was when the universe became transparent to light. At the time of the origin of the CMB the universe was completely filled with stuff at the temperatures typical of the surface of stars. And the surfaces of stars are hot, yes, but not exotically hot. They compare to the center of our planet for example, and aren't hard to create in labs. Some limited phenomena that happen in your house (fluorescent lights) are in or near that range on a small scale.

 

[acbytesla]

Like the surface of some stars.


Comparable to the surface of a star. It's a plasma and we wouldn't be talking exotic subatomic particles at this time. It would be ordinary protons (hydrogen nuclei), alpha particles (helium nuclei), and electrons. Very much similar to the stuff on the surface of the Sun.



The temperature at the time of the origin of the CMB is comparable to the surfaces of stars for the same reason. The surface of the star is the point where the star becomes transparent to light. The time of the CMB was when the universe became transparent to light. At the time of the origin of the CMB the universe was completely filled with stuff at the temperatures typical of the surface of stars. And the surfaces of stars are hot, yes, but not exotically hot. They compare to the center of our planet for example, and aren't hard to create in labs. Some limited phenomena that happen in your house (fluorescent lights) are in or near that range on a small scale.

Yeah, the surface of the Sun is not very hot at all compared to its corona. The CMB just after the Big Bang is estimated be around 3,000 Kelvin or about 5,000 degrees Fahrenheit. Whereas the Sun's surface is estimated to be about 6,000 Fahrenheit and its corona around 2 million degrees Fahrenheit.

This is where I get lost in the story. The CMB at this time is just not that hot. But still, it seems to be the perfect temperature to blind us from seeing further back and further away.

 

[RecoveringYuppy]

Blinding isn't the right way to think of it, it's blocking. It's a hot dense plasma that is opaque to light just like the stuff that is right under the surface of the Sun. Then it transitions to something like what is above the surface of the Sun which is transparent to light. And BTW that part would be the photosphere, not the Corona. The photosphere is a better analogy to the universe right after the origin of the CMB.

 

[acbytesla]

Blinding isn't the right way to think of it, it's blocking. It's a hot dense plasma that is opaque to light just like the stuff that is right under the surface of the Sun. Then it transitions to something like what is above the surface of the Sun which is transparent to light. And BTW that part would be the photosphere, not the Corona. The photosphere is a better analogy to the universe right after the origin of the CMB.

I was just saying that the CMB at this time is not really insanely hot. That its temperature is far lower than parts of our own star not to mention the temperatures of White and Blue Stars.

It seems strange to me that this soup of CMB of about 3000 Kelvin blocks out all these celestial objects that are much much hotter.

 

[RecoveringYuppy]

It seems strange to me that this soup of CMB of about 3000 Kelvin blocks out all these celestial objects that are much much hotter.

It doesn't block out any celestial objects. The entire universe had the consistency of the surface of a star at that time. Celestial objects came in to existence later.

 

[Puppycow]

Fascinating discussion.

Anyway, today is 100 days since the launch. MIRI is down to 26K according to the latest update. 19 deg. away from the target of 7K. The temperature plot looks more linear than I expected it to be. I thought the rate would be fastest at the beginning and slow down as it approached the target temp, but if anything it has sped up, dropping 15.8 deg. in the last 2 days.

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

 

[acbytesla]

It doesn't block out any celestial objects. The entire universe had the consistency of the surface of a star at that time. Celestial objects came in to existence later.

I would argue that we don't know that. Isn't it possible that there are stars and galaxies that predated this period, but we have no way to see them because of the CMB? We can only hypothesize anything before this period of time.

But admittedly my grasp of this science is very limited.

 

[RecoveringYuppy]

I would argue that we don't know that. Isn't it possible that there are stars and galaxies that predated this period, but we have no way to see them because of the CMB? We can only hypothesize anything before this period of time.

Well, no. We understand how materials at higher temperatures and pressures work so we're not just hypothesizing about anything that came before the decoupling. Our understanding of physics seems capable of projecting back a couple hundreds of thousands of years prior to that point.

We also know the universe was incredibly uniform at the decoupling. And how can you have stars and galaxies in a universe that is entirely filled with a plasma comparable to the surface of a star?

BTW the phrase "comparable to the surface" is a bit glib. It's comparable in chemical composition and temperature. Pressure and density are not so comparable. These details don't matter so far in this conversation though.

 

[smartcooky]

Fascinating discussion.

Anyway, today is 100 days since the launch. MIRI is down to 26K according to the latest update. 19 deg. away from the target of 7K. The temperature plot looks more linear than I expected it to be. I thought the rate would be fastest at the beginning and slow down as it approached the target temp, but if anything it has sped up, dropping 15.8 deg. in the last 2 days.

https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html

Passive cooling tends to follow that trend (which you can see by looking at the earlier lines in the plots) but active cooling tends to drive the temperature down quickly in a near-linear fashion, although remember, 7K is is getting near to absolute zero, so it could flatten out a little near the end.

ETA: From the Where is Webb page

"To manage the cooldown process, MIRI also has heaters onboard, to protect its sensitive components from the risk of ice forming. The Webb team has begun progressively adjusting both the cryocooler and these heaters, to ensure a slow, controlled, stable cooldown for the instrument. Soon, the team will turn off MIRI’s heaters entirely, to bring the instrument down to its operating temperature of less than 7 kelvins (-447 degrees Fahrenheit, or -266 degrees Celsius). "​

Judging by the way the temperature suddenly plunged today and yesterday...

... I would say they have now turned those heaters off.

 

[acbytesla]

Well, no. We understand how materials at higher temperatures and pressures work so we're not just hypothesizing about anything that came before the decoupling. Our understanding of physics seems capable of projecting back a couple hundreds of thousands of years prior to that point.
We also know the universe was incredibly uniform at the decoupling. And how can you have stars and galaxies in a universe that is entirely filled with a plasma comparable to the surface of a star?

BTW the phrase "comparable to the surface" is a bit glib. It's comparable in chemical composition and temperature. Pressure and density are not so comparable. These details don't matter so far in this conversation though.

We're not? I know man has created transuranium elements through fission. But has man synthesized lighter elements like helium, hydrogen or lithium etc? Now I have to learn particle physics.

By the way, I'm not debating you. I am trying grasp what is still a mystery to me.

 

[RecoveringYuppy]

We're not? I know man has created transuranium elements through fission. But has man synthesized lighter elements like helium, hydrogen or lithium etc?

Yes. Our fusion reactions in hydrogen bombs and particle accelerators have been synthesizing via fusion for quite a while. We've even created protons and anti-protons (that's hydrogen and anti-hydrogen) in accelerators.

 

[Ziggurat]

It seems strange to me that this soup of CMB of about 3000 Kelvin blocks out all these celestial objects that are much much hotter.

Why is that strange? The photosphere of the sun does the same thing. It’s a mere 6000K, but it blocks light from the core, which is millions of degrees.

You don’t need to be hot to be opaque.

 

[BowlOfRed]

We're not? I know man has created transuranium elements through fission

Not fission, but fusion. Just a form that takes energy rather than produces it.

But has man synthesized lighter elements like helium, hydrogen or lithium etc? Now I have to learn particle physics.

Yes, all sorts of common and nearly impossible isotopes have been created in accelerators and the energies and probabilities that are needed to create one from another are pretty well understood.

And you have to go back a long way prior to photon decoupling to have to worry about it anyway. The universe should be cool enough for nuclei to be stable (outside of stars, anyway) after about 20 minutes.

 

[Cheetah]

Ziggurat explained it well.

I would argue that we don't know that. Isn't it possible that there are stars and galaxies that predated this period, but we have no way to see them because of the CMB? We can only hypothesize anything before this period of time.

But admittedly my grasp of this science is very limited.

There cannot be any celestial objects beyond the CMB. If you could see beyond the CMB, all you would observe is the universe growing ever hotter and denser.
I wonder if it’s theoretically possible using gravity waves?

 

[RecoveringYuppy]

Ziggurat explained it well.

There cannot be any celestial objects beyond the CMB. If you could see beyond the CMB, all you would observe is the universe growing ever hotter and denser.
I wonder if it’s theoretically possible using gravity waves?

Yep, that's theoretically possible. Also possible that neutrinos can be observed from beyond that point.

 

[acbytesla]

Not fission, but fusion. Just a form that takes energy rather than produces it.

No, i meant fission. The process of fission (not fusion) results in the formation of elements including plutonium, xenon, strontium, ceasium and others. The man-made transuranic elements are the result of fission reactions.

 

[Puppycow]

Judging by the way the temperature suddenly plunged today and yesterday...

... I would say they have now turned those heaters off.

That or maybe it has variable output. The Where is Webb page says it is in "stage 4" whereas the most recent blog post on the mission blog says that it is turned on in "two stages".

Final Cooldown: Track MIRI's temperature (trace 1) to its target operational level (below 7K) with the cryo-cooler now in stage 4.

Interspersed within the initial MIMF observations, the two stages of the cooler will be turned on to bring MIRI to its operating temperature.

 

[Ziggurat]

No, i meant fission. The process of fission (not fusion) results in the formation of elements including plutonium, xenon, strontium, ceasium and others. The man-made transuranic elements are the result of fission reactions.

This is wrong. Fission creates lighter elements than you start with, not heavier elements.

For example, plutonium is primarily created by neutron capture and beta decay from uranium. Which is neither fission nor fusion, but is closer to fusion than fission. Some of the really heavy synthetic elements are created by even more exotic methods.