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Jzz

May 10, 2021
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Hi Jzz - nothing amiss!

Actually, some of the hiss of radio/tv static is CMB!

Most electromagnetic radiation (of all wavelengths) is generated by so-called thermal sources: fusion or other forms of heating. (Some is "non-thermal", generated by, primarily magnetic fields and their interaction with electrons).

These thermal sources (stars, gas clouds, etc) radiate at all wavelengths (more or less) but the peak fo their emission varies with temperature, and the photons with wavelengths off the peak could be few and far between. For example, the Sun's surface is some 6,000 degrees. The peak of emission of the solar surface is in the middle of the visible part of the spectrum (of course), but there are also other photons, X-ray, gamma-ray, UV, radio, IR. But at lower numbers. A cold gas cloud (the state that most hydrogen is in for a galaxy like ours) emits most of its electromagnetic radiation in the radio. There are SOME photons at other wavelengths but relatively few. Certainly the gas clouds absorb photons, and the energy imparted lead to that 21cm wavelength emission line I mentioned originally.

Keep in mind that most hydrogen is locked up in stars (only about 10%, give or take, is in the form of interstellar gas clouds).

By the way, I'm not saying the universe is quiescent - far from it. But the preceeding gives a (very high level) picture of the electromagnetic radiation field. And you are correct about the neutrinos (but they are barely interacting with anything). By the way, there are far more photons zipping around than there are particles of matter, and they are mostly the microwave photons from the CMB.

Dr. Joe
Dr Joe. Your superb answers are very much appreciated. I am very much indebted to hear these explanations at first hand. However, I should point out that the explanation of the hyperfine transitions in atoms is not so facilely explained as present theories make out. If you remember Lamb and Bethe working on the problem of hyperfine structure transitions in the late 1940’s, came to the conclusions that the electron as it orbits the nucleus is constantly emitting and absorbing ‘virtual photons’. (i.e., undergoing virtual transitions) this is the Lamb shift. These virtual photons are exactly the same as ordinary photons with the exception that the interactions last for such short periods of time that they are to al purposes ignored by the laws of conservation of energy and momentum. Therefore, the idea of a spin flip is not entertained in this theory. These virtual transitions explain how the electron self regulates its energy and is able to remain in orbit around the nucleus without falling in. Surely such a theory is, if not better, at least equally acceptable as the sometimes wave sometimes particle theory of quantum mechanics?

To diverge for a moment. How does mainstream physics use this explanation and then blandly state that the term photon frequency is a misnomer, it doesn’t exist it is a mathematical abstraction used to explain the energy of a photon. Yet, in these hyperfine structure transitions, photon frequencies are very clearly seen. The crucial point is that microwaves with a frequency of 1420405751.768(2) Hz have such extremely low energy that they cannot possibly overcome the opposing electrostatic and lets’ face it even gravitational forces within the atom. Therefore, what happens is that when an atom is raised to a metastable state the only way in which it can release its energy is to emit ‘conduction photons’ which form micro currents that radiate at exactly 1420405751.768(2) Hz! Which is the excess energy gained. Thus, it is possible for the atom to mediate its energy by emitting conductions photons which give rise to micro currents that radiate at 1420405751.768(2) Hz.

Again, the 21 cm hydrogen line is of huge importance, its redshift allows the rotational speed of galaxies to be calculated and its relatively long wave-length also enables the mapping of the Galaxies and of the Universe. How can this be explained by these two conflicting ideas? Same result, different solutions to getting there. I had written a paper on this entitled: “Some new ideas in Physics” (see link below😊 It gets interesting from about the last para on page 13.

 

DrJoePesce

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Agreed, I understand all that you’ve said, but my argument is more nuanced, perhaps.

Let’s make your rubber band 2 meters in length (1m L&R) so a 1cm stretch on both ends, keeping the middle point the same, becomes an expansion of 1%. But, and this is my question, any given segment will also stretch 1%. So the first mm in length from the center will stretch, in this case, 10 microns.

So, if our universe has expanded, say, 10% since its nascent days many billions of years ago, it’s hard to expect our galaxy to have expanded that same 10%, again ignoring dwarf consumptions.😉

Worse, since most atomic H is primordial, it seems likely that its electron’s orbit will not now be 1100x greater in radius from the proton due to expansion since Recombination.

Or am I still missing something?

Thanks for your patience!

Perhaps others can assist us .

iPhone
The expansion rate is something like 65 km per second per Megaparsec (implying that it is operating on the largest scales).

If we "down convert" that to the expansion rate on the centimeter scale, my back-of-the envelope calculation gives 10^-24 km per second per cm. So expansion on the cm scale is miniscule, even over the age of the universe. (Again, in the distant future this will change.) Remember also that because this is so small, local effects of gravity, strong and weak nuclear force, are far more important and dominate the universal expansion. That's why our satellite galaxies are flying away from us, and the Milky Way isn't being torn apart. Yet.... That will happen in the future.
 
The expansion rate is something like 65 km per second per Megaparsec (implying that it is operating on the largest scales).

If we "down convert" that to the expansion rate on the centimeter scale, my back-of-the envelope calculation gives 10^-24 km per second per cm. So expansion on the cm scale is miniscule, even over the age of the universe. (Again, in the distant future this will change.)
Agreed, but this is still ~1/2 mm/cm since Recombination.

Remember also that because this is so small, local effects of gravity, strong and weak nuclear force, are far more important and dominate the universal expansion. That's why our satellite galaxies are flying away from us, and the Milky Way isn't being torn apart.
Yes, this is the clarity I’ve been seeking since I had inferred that space is expanding at all levels. IOW, galaxies and the radii of atoms as well, which seemed unlikely.

Thanks.
 

DrJoePesce

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The expansion rate is something like 65 km per second per Megaparsec (implying that it is operating on the largest scales).

If we "down convert" that to the expansion rate on the centimeter scale, my back-of-the envelope calculation gives 10^-24 km per second per cm. So expansion on the cm scale is miniscule, even over the age of the universe. (Again, in the distant future this will change.) Remember also that because this is so small, local effects of gravity, strong and weak nuclear force, are far more important and dominate the universal expansion. That's why our satellite galaxies are flying away from us, and the Milky Way isn't being torn apart. Yet.... That will happen in the future.
And I think I know what the disconnect is - and it's my fault!

I've brought us the cm/m scale with the numbers above. But we need to go further, and everything I've said above is actually a billionth or 10 billionth smaller for the atomic scales (so my numbers above should be 10^-33 or 10^-34 on those scales).

Dr. Joe
 
I think napkins are too small for these numbers. :)

So, here is my Excel attempt at it...

View: https://imgur.com/a/YBYCdC9


This, if correct, shows about 1 cm of expansion for each original cm from 13.8 Gyrs ago. But this isn't quite correct since the expansion rate at 2 cm is 2x that for 1 cm, thus the actual expansion for 1 cm would stretch it's original length to become about 2.5 cm.

Thanks for your diligence on this interesting topic. :)
 
Mar 27, 2020
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I recently read that the observable universe is some 93 billion light years across. And yet, the universe's age is less than 13 billion years. So is expansion faster than the speed of light? How do we account for this discrepancy? Thanks, Joe!
 
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DrJoePesce

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I recently read that the observable universe is some 93 billion light years across. And yet, the universe's age is less than 13 billion years. So is expansion faster than the speed of light? How do we account for this discrepancy? Thanks, Joe!
Thanks for the question Josh. These sorts of things are mind numbing, aren't they? One thing first: The age of the universe is measured from the cosmic microwave background (CMB) as 13.8 billion years.

The 93 billion light year diameter (assuming the universe is a sphere) comes from the assumption that inflation is constant, and over 13.8 billion years that's the size you get if so.

Remember, we talk about the observable universe having a radius of 13.8 billion light years. There are parts of the universe that are not observable, right? Even if we ignore the constant inflation issue, the diameter of the universe is at least 27.7 billion light years. Meaning that there are parts of the universe that can't "communicate" with each other (or, put another way, that will be forever beyond the visible (observable) horizon from each other).

By the way, this, and the finding that the temperature fluctuations of the CMB are minuscule, led to the modification of the big bang theory, creating the inflationary model which is in force today. In a nutshell, the small temperature variations mean that very early in its history all parts of the universe were in contact with each other, and the temperature was able to smooth out everywhere. But the universe today is too large for that to have ever happened. This is called the "isotropy problem".

Thus, inflation was postulated: The temperatures smoothed out when the universe was very small, and then inflation kicked in and it inflated from the size of an atom to the size of a grapefruit in a minuscule fraction of a second. After that, it expanded at a more or less constant rate. This inflationary epoch was caused by what we now call dark energy. And dark energy kicked in again about a billion years ago and caused the expansion to accelerate.

Coming back to a universe with diameter 93 billion light years: That implies the universe is expanding faster than the speed of light (as it certainly did during that inflationary period I just mentioned). And the answer is yes it does. Remember, that while we measure expansion by measuring the recessional velocity of galaxies, the galaxies themselves are not moving, but rather the space between them is expanding. Because of this we don't violate the ultimate speed limit, because "stuff" isn't moving faster than light.

I hope that helps in a small way to shed some light on this. There are all sorts of factors at play here to get the ultimate answer regarding the size of the universe:

- was inflation really constant? (I don't think it has been over the past 1 billion years, for example). Were there other such fluctuations over the history of the universe? And there are some indications the acceleration is slowing.

- the shape of the universe affects the size as well. The above assumes the universe is sphere (which I think is correct, for what my opinion is worth!), but it could be flat or saddle shaped.

Dr. Joe
 
Jun 17, 2022
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Dear Dr Joe,

I live in the UK and one of the things that I love about the summer months is when it's hot and I get to sit in the garden at night and stare up into the sky.

This always gets me thinking about several theoretical existential questions, the main one always being, is space infinite?

I read that alot of experts believe that we exist within a spatial doughnut, however, I think this is a cop out for those that can't comprehend infinite mass.

What is your theory on this?

Thanks,
Poodlepupboy
 

DrJoePesce

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Dear Dr Joe,

I live in the UK and one of the things that I love about the summer months is when it's hot and I get to sit in the garden at night and stare up into the sky.

This always gets me thinking about several theoretical existential questions, the main one always being, is space infinite?

I read that alot of experts believe that we exist within a spatial doughnut, however, I think this is a cop out for those that can't comprehend infinite mass.

What is your theory on this?

Thanks,
Poodlepupboy

Hi Poodlepupboy!

That sounds lovely! I have a nice place to look up and think, too.

The full answer to your excellent question is a complicated one and requires a lot of speculation that may or may not be sound. So let's skip that.

I think the answer is no, it's not infinite. One (maybe partial) answer to this is the answer to the so-called Olber's Paradox. If the universe were infinite, the night sky would not be dark. Why? Because, if so, everywhere we look we will eventually encounter photons from a star. Hence, the night sky will not be dark. Hans Olbers thought about this in the 19th century. The answer to the paradox is that the universe is not infinite!

One thing I would like to gently correct: We don't have a universe with infinite mass.
Otherwise, we would have collapsed into a black hole, or be on our way to collapsing. The universe is not collapsing, but rather expanding and that puts a limit on the mass present in the universe. Mass = gravity so if there's enough mass it will slow the expansion. If even more, it will stop the expansion and reverse it

Keep looking up and thinking!

Dr Joe
 
Jun 17, 2022
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Hi Poodlepupboy!

That sounds lovely! I have a nice place to look up and think, too.

The full answer to your excellent question is a complicated one and requires a lot of speculation that may or may not be sound. So let's skip that.

I think the answer is no, it's not infinite. One (maybe partial) answer to this is the answer to the so-called Olber's Paradox. If the universe were infinite, the night sky would not be dark. Why? Because, if so, everywhere we look we will eventually encounter photons from a star. Hence, the night sky will not be dark. Hans Olbers thought about this in the 19th century. The answer to the paradox is that the universe is not infinite!

One thing I would like to gently correct: We don't have a universe with infinite mass.
Otherwise, we would have collapsed into a black hole, or be on our way to collapsing. The universe is not collapsing, but rather expanding and that puts a limit on the mass present in the universe. Mass = gravity so if there's enough mass it will slow the expansion. If even more, it will stop the expansion and reverse it

Keep looking up and thinking!

Dr Joe
Thank for your message Dr Joe,

Your response made me feel somewhat of a hypocrit in that I always condescended those who couldn't grasp on to the fact that space was infinite whereas I cannot actually comprehend space not being infinite.

Would be good to learn more about this as I can't imagine space having an edge (maybe we're the intergalactic christopher columbus' 😅).

I supposed I've always fantasized that the possibility of infnlinte space means the endless possibility of life out there, however, this almost link's to string theory, I think, but not quite.

Wish I had like-minded folk around here to talk with about this as space is humanities only hope...
 
Apr 29, 2022
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Dr. Joe,

What do you think of the new James Webb Space telescope images and how do you think that that will affect how the public sees space?
 

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Dr. Joe,

What do you think of the new James Webb Space telescope images and how do you think that that will affect how the public sees space?
Hi Orion! '

I've just posted some pieces from an interview at NSF showing my reactions (also here: https://www.youtube.com/watch?v=ulWAn623l9Q). The summary is: The images are fantastic, and the JWST is a phenomenal instrument, as we expected it to be. I am really excited to see what comes from it's (hopefully) very long tenure.

In addition to it's place in science history (and the provision of data that will advance human understanding), the role JWST, and these outreach events, play in the broader human experience are incalculable.

I have no doubt that some young child somewhere on Earth will see these images and that will spark a desire to become an astrophysicist. And it will be more than one: Lots of children will be influenced this way (by the way, it seems this is the common path for an individual to take to become a professional astronomer - influence like this at a very early age - it's my story, in fact).

This is great - it's great for the field and for human knowledge advancement.

But of even greater importance, millions of individuals will be inspired by these amazing images: inspired in life, in art, in an appreciation of science. Some of them might go into STEM fields. The majority won't but they will have become advocates for astronomy. And, as I've said many times before, astronomy is a gateway science. JWST sparks an interest, and then the individual's eyes are open to the whole world of STEM.

This is why the broader impact (as we at NSF call it) aspect of scientific research is so vitally important.

But you asked perhaps a slightly different question: Our astronomical observations influence how the public understands, and expects to see future, scientific results. I have a wonderful friend and colleague who is an astrosociologist and has studied how presentation of images (think the Event Horizon Telescope black hole images) impacts people; it's fascinating.

JWST is observing in a non-intuitive region of the electromagnetic spectrum (that we can't otherwise see with our eyes). This has a much larger impact than one might expect (think images from radio telescopes, which are something that are otherwise completely alien to our sensory experience). Having said that, JWST images are in a region of the electromagnetic spectrum that isn't too far removed from the visual portion we experience. So, things look more or less as we intuitively think they should be. I think the bigger impact, though, is that JWST is such a spectacular instrument we are seeing unprecedented detail - and that will definitely impact how all of us expect to see astronomical images from now on.

Dr Joe
 

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Hi Joe

Is it possible to build a combined (planet-wide) optical telescope similar to the EHT radio telescope that pictured a black hole and would we then be able to look at nearby star systems and their planets with resolutions comparable to the EHT image?

Thanks
Hi Joshua - thanks for the post. It's been quiet around here and I was just going to see how everyone is doing. I guess you are all poring over the JWST images!

Inteferometery! It's a subject near to my heart, as the official responsible for most of the US's radio astronomy facilities, through the NSF's National Radio Astronomy Observatory (NRAO.edu).

The observatories in my portfolio - the Very Large Array (VLA), the Very Long Baseline Array (VLBA), and the Atacama Large Millimeter/submm Array (ALMA) - are all interferometers working in the radio portion of the electromagnetic spectrum.

You ask about an optical interferometer. Such an instrument is possible. But optical photons have much higher frequency than the radio photons we are detecting with the arrays discussed above. There are other issues, but fundamentally the time-stamping requirement is far more stringent in the optical than in the radio, so much so that we don't really have the technology to do this. So what is done in the limited experiments to date is create optical delay lines (using fiber optics) to delay the optical signal from the various telescopes in the array. This is difficult, and I think can only be done for telescopes relatively close together.

Bottom line: An optical interferometer is possible, but it's technically difficult and not feasible with current technology.

With such an interferometer, we would indeed be able to see exquisite detail in astronomical objects. Note the objects you mention are, to a greater or lesser extent, already visible with radio telescopes as well as single mirror optical/infrared telescopes.

Now let me go back to the radio inteferometer example to give a bit more detail on what is happening.

Each element of the array observes the astronomical target simultaneously and, together, they form the equivalent of a single dish in the radio (or mirror in the optical) whose diameter is the distance between the most distant elements of the array. (It's not exactly like a single dish/mirror, because lots of photons from the astronomical source are lost between the individual telescopes, so the array doesn't have the sensitivity of a single dish/mirror but the resolution - the ability to see fine detail - is far superior to a single dish/mirror).

This activity is easier said than done, however. Fundamentally, as the photons come in to each telescope, and are converted into an electrical signal, a time stamp is injected into the data stream. For the radio, this has to be done at the nano-second (1 billionth of a second) scale. The data stream of each telescope is then compared to those of all the other telescopes in the array and the time-stamping allows the data to be lined up and the single telescope simulated. The computing requirements for this are enormous and is done by a dedicated supercomputer called a correlator: The correlator at ALMA is the fastest computer on Earth, but it only does lots of multiplication operations, and not much else.

Hope this helps!

Dr Joe
 
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Mar 27, 2020
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Joe -- as a gravitational wave passes, do atoms and molecules distort, or just the fabric of space time in which they reside? If just the fabric, is the fabric the only "material" directly affected (save teh stretching of photons)?
 

DrJoePesce

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Is it possible to use planets as telescopes for real world applications? As presented in this video.

View: https://www.youtube.com/watch?v=jgOTZe07eHA&t=1551s
Thanks for this. Very interesting. Certainly this is possible, theoretically, but as noted in the video it would be very difficult to do in practice. Gravitational lensing, of the sort this video mentions (but with stars), has been used in astronomical satellite missions.

Dr Joe
 

DrJoePesce

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Joe -- as a gravitational wave passes, do atoms and molecules distort, or just the fabric of space time in which they reside? If just the fabric, is the fabric the only "material" directly affected (save teh stretching of photons)?
Hey Josh, Thanks for the great question. The waves are affecting space time, which is the material being stretched and compressed.

But everything is embedded in space time, since space time is being distorted, the subatomic particles that make up atoms and molecules are being distorted too.

As for stretching of photons: Are you referring to the so-called redshift (light that has traveled from distant objects has been shifted redward, the more distant the redder)? That's a different process: As those photons are traveling through space, space is expanding and that is what stretches (makes longer) their wavelengths, hence making them redder.

Or, do you mean, the gravitational redshift of photons escaping from near a black hole (or any gravitating mass for that matter)? In this case, the distortion of space time caused by the gravitating mass stretches the photons' wavelength as they pull away from the mass. This is known as gravitational redshift (and is a redshift because, again, the wavelength is stretched and gets longer, the longer wavelength the redder the photon). These processes, though involving the distortion of space time (from expansion in the former example and gravity in the latter), are not the same as a gravitational wave traveling through space.

Dr Joe
 

Catastrophe

"There never was a good war, or a bad peace."
Hi Dr Joe, you wrote above
The waves are affecting space time, which is the material being stretched and compressed.
To the non expert (me :) ) it seems more and more that we are reverting to the good, old, discredited aether. Is there a fairly quick and easy answer to highlight the differences? Many thanks in advance,

Cat :)
 

DrJoePesce

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Hi Dr Joe, you wrote aboveTo the non expert (me :) ) it seems more and more that we are reverting to the good, old, discredited aether. Is there a fairly quick and easy answer to highlight the differences? Many thanks in advance,

Cat :)
Hi Cat! Well, aether in the "classical" sense, fills/permeates space. What I'm talking about in the extract above IS space: The fabric of space itself is affected by the gravitational wave as it travels (at the speed of light) through space.

Dr Joe
 

Catastrophe

"There never was a good war, or a bad peace."
Thank you Dr Joe. What I had in mind, was that the old aether (if I understand it correctly, and it is about 65 years since I first came across the MME) related to the difference between Newtonian space as a mathematical coordinate system with no physical reality, and a 'space' which was inhabited by a 'real' substance able to 'carry', or facilitate propagation of light. IIRC, the MME came down against the latter.

When you put
space time, which is the material being stretched and compressed
it just 'rang a little bell' with me, as it sounded just like the classical aether, and just what the MME 'disproved'. I asked the question in a genuine desire to better understand the difference., and to understand where I have got it wrong. I am not a cosmologist - just a humble retired chemical engineer, interested in the subject. My expertise was in surfactant chemistry, on which inter alia I edited a book for Marcel Dekker. I have never been a professional astrophysicist.

Cat :)
 

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