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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

Verified Expert
Mar 31, 2020
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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

Verified Expert
Mar 31, 2020
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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

Verified Expert
Mar 31, 2020
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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...
 

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