James Webb Telescope

[acbytesla]

That’s just it, our observable universe cannot grow using a better telescope. We will just have more detail.

No, that's not correct. We will see more detail and further.

The JWST's larger mirror and infrared cameras will be able to see further into space. It will be able to detect not only more visible light, but light from galaxies previously unseeable because the light waves from them have stretched into the mid-infrared spectrum.

 

[RecoveringYuppy]

No, that's not correct. We will see more detail and further.

The JWST's larger mirror and infrared cameras will be able to see further into space. It will be able to detect not only more visible light, but light from galaxies previously unseeable light because the light waves from them have stretched into the mid-infrared spectrum.

Right, but that isn't a new region of space, it's a new portion of the spectrum.

 

[zooterkin]

Right, but that isn't a new region of space, it's a new portion of the spectrum.

But seeing that part of the spectrum lets us, effectively, see further back in time. (See the diagram towards the bottom of the page on that link.)

 

[slyjoe]

But seeing that part of the spectrum lets us, effectively, see further back in time. (See the diagram towards the bottom of the page on that link.)

By about 700,000,000 years. Certainly not billions.

 

[RecoveringYuppy]

By about 700,000,000 years. Certainly not billions.

And we've already seen further back in time using other parts of the spectrum.

 

[Ziggurat]

That’s just it, our observable universe cannot grow using a better telescope. We will just have more detail.

No, that's not correct. We will see more detail and further.

No, it is correct. The size of the universe we can see (with light) is limited by the CMB, which we already see. That's the observable universe. You would need to use something like neutrinos or gravitational waves to see further, and I don't think our detection technology is good enough yet to do that with either. What JWST will do is allow us to see things within the visible universe that we cannot currently see, but all of it is still closer to us than the CMB, and so it doesn't expand the observable universe.

 

[acbytesla]

By about 700,000,000 years. Certainly not billions.

Much depends on the accuracy of certain accepted hypotheses like the Big Bang. On one hand JWST should be able to see much much farther in distance than the 13.9 billion years away. But since present estimates date the Universe at about 13.9 billion years, that would be the theoretical limit of the observable universe. Further away than that the cosmic radiation background blinds even the MIRIcam.

 

[RecoveringYuppy]

Further away than that the cosmic radiation background blinds even the MIRIcam.

Well then that's a shame the engineers included an instrument that won't be usable.

How far away an object can be seen isn't strictly a function of the instrument. It's a function of both the instrument and the object being observed. In plain English, bright things can be seen further.

 

[Ziggurat]

Well then that's a shame the engineers included an instrument that won't be usable.

How far away an object can be seen isn't strictly a function of the instrument. It's a function of both the instrument and the object being observed. In plain English, bright things can be seen further.

I think you missed his point. The CMB is basically an optical wall. You can't see past the CMB because the source of the CMB is opaque. Even if there were something sufficiently bright behind it, it would still be invisible to us, because light from it could not pass through the CMB source. Not that there are any stars or galaxies past the CMB source anyways, since the CMB predates the first stars and galaxies.

 

[RecoveringYuppy]

I think you missed his point. The CMB is basically an optical wall. You can't see past the CMB because the source of the CMB is opaque. Even if there were something sufficiently bright behind it, it would still be invisible to us, because light from it could not pass through the CMB source. Not that there are any stars or galaxies past the CMB source anyways, since the CMB predates the first stars and galaxies.

No, I got that. I'm not sure he did though from his phrasing.

 

[acbytesla]

Well then that's a shame the engineers included an instrument that won't be usable.

It is usable. It's just limited in its use.

How far away an object can be seen isn't strictly a function of the instrument. It's a function of both the instrument and the object being observed. In plain English, bright things can be seen further.

This goes without saying. But in this case, the limitation is that the light gets lost in the Cosmic Radiation Background.

 

[RecoveringYuppy]

It is usable. It's just limited in its use.

Of course. All devices are limited somehow. But the CMBR doesn't seem to have much relationship here. What limitation do you have in mind (see next question)? My statement was half joking by the way, and half intended to get an explanation.

This goes without saying. But in this case, the limitation is that the light gets lost in the Cosmic Radiation Background.

We can't see back in time before the point that the CMBR was created because the universe was opaque then. Is that what you mean?

 

[Ziggurat]

This goes without saying. But in this case, the limitation is that the light gets lost in the Cosmic Radiation Background.

What do you mean by "gets lost"?

In my original reading of your prior post, I thought you were referring to the fact that the source of the CMB is opaque. Do you instead mean that a source in front of the CMB will be invisible because the CMB will wash out the signal from it? That seems to be how RY is interpreting you.

Because if it's the latter, I don't think that's generally going to be the case. The source of the CMB was only about 3000K at the time. It will have redshifted significantly even before the first stars, and the first stars should mostly have temperatures much higher than 3000K. So even after all the subsequent redshifting, they should have spectra well above the CMB.

 

[acbytesla]

Of course. All devices are limited somehow. But the CMBR doesn't seem to have much relationship here. What limitation do you have in mind (see next question)? My statement was half joking by the way, and half intended to get an explanation.



We can't see back in time before the point that the CMBR was created because the universe was opaque then. Is that what you mean?

Yes. One cannot differentiate between the Cosmic Radiation Background and light from a distant galaxy. I'd describe it kind of like trying to see someone dressed entirely in white against a snowfield.

 

[Ziggurat]

Yes. One cannot differentiate between the Cosmic Radiation Background and light from a distant galaxy. I'd describe it kind of like trying to see someone dressed entirely in white against a snowfield.

I don't think this is correct. If the galaxy is in front of the CMB, then it's going to be emitting at shorter wavelength. The CMB was not actually very hot even at the time, only ~3000K. There's going to be a lot of stars much hotter than that, with spectra at shorter wavelengths than the CMB, no matter how far back you go. So it's not going to be white against white, it's going to be white against red.

 

[RecoveringYuppy]

Yes. One cannot differentiate between the Cosmic Radiation Background and light from a distant galaxy. I'd describe it kind of like trying to see someone dressed entirely in white against a snowfield.

OK. What Ziggurat just said. The CMBR and the light of distant galaxies aren't in the same part of the spectrum. They might overlap a bit but not significantly.

The most distant objects that JWST will be looking at will be hotter and nearer/more recent than the CMBR so they won't overlap much.

 

[acbytesla]

Never mind.

This is one of those subjects that the more I study it, the more confused I become. The combination of expanding universe, the speed of light, the wavelength shifting of light etc, has a tendency to boggle my mind.

Just when I think i understand it, I learn I have to go back to square one.

 

[RecoveringYuppy]

Never mind.

This is one of those subjects that the more I study it, the more confused I become. The combination of expanding universe, the speed of light, the wavelength shifting of light etc, has a tendency to boggle my mind.

Just when I think i understand it learn I have to go back to square one.

No problem. Sorting out how far it is to the edge of the universe is not a simple thing. I certainly don't know it off the top of my head.

 

[acbytesla]

No problem. Sorting out how far it is to the edge of the universe is not a simple thing. I certainly don't know it off the top of my head.

And yet for physicists it seems to be. One of my favorite Youtube channels is Dr. Becky. She seems to be able to explain it as well as anybody.

 

[acbytesla]

No problem. Sorting out how far it is to the edge of the universe is not a simple thing. I certainly don't know it off the top of my head.

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.