Krishna: The photon (from Ancient Greek phôs, phōtós means 'light') is a type of elementary particle that serves as the quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force (3). 

In fact, once it expanded and cooled down a bit, the entire universe was merely as hot and as dense as the core of a star like our sun. It was cool enough for ionized atoms of hydrogen to form.

Because the universe has the conditions of the core of a star, it had the temperature and pressure to actually fuse hydrogen into helium and other heavier elements. Based on the ratio of those elements we see in the universe today: 74% hydrogen, 25% helium and 1% miscellaneous, we know how long the universe was in this "whole universe is a star" condition.

It lasted about 17 minutes (Universe's time scale). From 3 minutes after the Big Bang until about 20 minutes after the Big Bang. 

The fusion process generates photons of gamma radiation. In the core of our sun, these photons bounce from atom to atom, eventually making their way out of the core, through the sun's radiative zone, and eventually out into space. This process can take tens of thousands of years. But in the early universe, there was nowhere for these primordial photons of gamma radiation to go. Everywhere was more hot, dense universe.

The universe was continuing to expand, and finally, just a few hundred thousand years after the Big Bang, the universe was finally cool enough for these atoms of hydrogen and helium to attract free electrons, turning them into neutral atoms.

And this is the earliest possible light that astronomers can see.

The cosmic microwave background radiation. Because the universe has been expanding over the 13.8 billion years from then until now, the those earliest photons were stretched out, or red-shifted, from ultraviolet and visible light into the microwave end of the spectrum.

If you could see the universe with microwave eyes, you'd see that first blast of radiation in all directions. 

After that first blast of light, everything was dark, there were no stars or galaxies, just enormous amounts of these primordial elements. At the beginning of these dark ages, the temperature of the entire universe was about 4000 kelvin. Compare that with the 2.7 kelvin we see today. By the end of the dark ages, 150 million years later, the temperature was a more reasonable 60 kelvin (1).

The universe had a lot of settling to do. The cold gas is the key to making stars, and so it’s been since the beginning. And the Big Bang was nothing if not hot. The material it made took millennia to settle down just enough to form the simplest atoms, a single proton and electron joining forces to form hydrogen. To calm down enough for those atoms to stick together, for gravity to take hold and start collapsing clouds of hydrogen gas, took much longer (4).

For the next 850 million years or so, these elements came together into monster stars of pure hydrogen and helium. Without heavier elements, they were free to form stars with dozens or even hundreds of times the mass of our own sun. These are the Population III stars, or the first stars, and we don't have telescopes powerful enough to see them yet. Astronomers indirectly estimate that those first stars formed about 560 million years after the Big Bang.

Then, those first stars exploded as supernovae, more massive stars formed and they detonated as well. It's seriously difficult to imagine what that time must have looked like, with stars going off like fireworks. But we know it was so common and so violent that it lit up the whole universe in an era called reionization. Most of the universe was hot plasma.

Stars like these would burn hotter than a star like our sun, and that in turn would unleash powerful amounts of ultraviolet radiation. When scientists look for this first generation of stars (confusingly called Population III stars), that fingerprint of brilliant UV light on the star’s surroundings is what they look for. Some even purport to have found it, at only 190 million years post-Big Bang, half the age of the universe that scientists expected.

So the universe birthed enormous stars, which burned through their nearly-pure hydrogen fuel quickly, in only a few million years. Physics only requires about 100 solar masses before a star is destined to end its life as a supernova. So these behemoths definitely exploded, unleashing a slew of heavy elements into the cosmos, polluting it and changing the composition of the universe forever more.

These massive stars and the black holes they created attracted more stars around them, and the first galaxies began to emerge. Stars of all sizes were born in new stellar nurseries. And the universe as we know it now finally began to appear (4).

Origin Of Light in the Sun

You asked about a single first photon. That is difficult to answer because we can only think about a flash of light, not a single photon.

Footnotes:

1. https://phys.org/news/2016-11-universe.html#:~:text=This%20was%20th....

2. https://svs.gsfc.nasa.gov/11084

3. https://en.wikipedia.org/wiki/Photon#:~:text=The%20photon%20(from%20Ancient%20Greek,carrier%20for%20the%20electromagnetic%20force.

4. https://astronomy.com/news/2018/10/when-the-lights-first-turned-on-...

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Q based on this artile .....

Q: Did the universe originate 13 billion years ago? 

Krishna: Scientists' earlier models estimate the universe to be 13.8 billion years in age, based on the big-bang expanding universe concept.

However, some scientists are proposing new models and these new theories suggest that it's been around for twice as long as thought!

I am posting here an article from THE CONVERSATION ( under a creative common licence) which tells us why.

 

How old is the universe exactly?

Early universe observations by the James Webb Space Telescope (JWST) cannot be explained by current cosmological models. These models estimate the universe to be 13.8 billion years in age, based on the big-bang expanding universe concept.

My research proposes a model that determines the universe's age to be 26.7 billion years, which accounts for the JWST's "impossible early galaxy" observations.

Impossible early galaxies refer to the fact that some galaxies dating to the cosmic dawn—500 to 800 million years after the big bang—have disks and bulges similar to those which have passed through a long period of evolution. And smaller in size galaxies are apparently more massive than larger ones, which is quite the opposite of expectation.

Frequency and distance

This age estimate is derived from the universe's expansion rate by measuring the redshift of spectral lines in the light emitted by distant galaxies. An earlier explanation of the redshift was based on the hypothesis that light loses energy as it travels cosmic distances. This "tired light" explanation was rejected as it could not explain many observations.

The redshift of light is similar to the Doppler effect on sound: noises appear to have higher frequency (pitch) when approaching, and lower when receding. Redshift, a lower light frequency, indicates when an object is receding from us; the larger the galaxy distance, the higher the recessional speed and redshift.

An alternative explanation for the redshift was due to the Doppler effect: Distant galaxies are receding from us at speeds proportional to their distance, indicating that the universe is expanding. The expanding universe model became favored by most astronomers after two astronomers working for Bell Labs, Arno Penzias and Robert Wilson, accidentally discovered cosmic microwave background (CMB) radiation in 1964, which the steady-state model could not satisfactorily explain.

The rate of expansion essentially determines the age of the universe. Until the launch of the Hubble Space Telescope in the 1990s, uncertainty in the expansion rate estimated the universe's age ranging from seven to 20 billion years. Other observations led to the currently accepted value of 13.8 billion years, putting the big-bang model on the cosmology pedestal.

A NASA animation showing how light from distant galaxies is stretched by the expansion of the universe.

Limitations of previous models

Research published last year proposed to resolve the impossible early galaxy problem using the tired light model. However, tired light cannot satisfactorily explain other cosmological observations like supernovae redshifts and uniformity of the cosmic microwave background.

I attempted to combine the standard big-bang model with the tired light model to see how it fits the supernovae data and the JWST data, but it did not fit the latter well. It did, however, increase the universe's age to 19.3 billion years.

Next, I tried creating a hybrid model comprising the tired light and a cosmological model I had developed based on the evolving coupling constants proposed by British physicist Paul .... This fitted both the data well, but almost doubled the universe's age.

The new model stretches galaxy formation time 10 to 20 fold over the standard model, giving enough time for the formation of well-evolved "impossible" early galaxies as observed.

As with any model, it will need to provide a satisfactory explanation for all those observations that are satisfied by the standard cosmological model.

Mixing models

The approach of mixing two models to explain new observations is not new. Isaac Newton considered that light propagates as particles in his theory of light, which prevailed until it was replaced by the wave theory of light in the 19th century to explain diffraction patterns observed with monochromatic light.

Albert Einstein resurrected the particle-like nature of light to explain the photoelectric effect—that light has dual characteristics: particle-like in some observations and wave-like in others. It has since become well-established that all particles have such dual characteristics.

Another way of measuring the age of the universe is to estimate the age of stars in globular clusters in our own galaxy—the Milky Way. Globular clusters include up to a million stars, all of which appear to have formed at the same time in the early universe.

Assuming all galaxies and clusters started to form simultaneously, the age of the oldest star in the cluster should provide the age of the universe (less the time when the galaxies began to form). For some stars such as Methuselah, believed to be oldest in the galaxy, astrophysical modeling yields an age greater than the age of the universe determined using the st..., which is impossible.

Einstein believed that the universe is the same observed from any point at any time—homogeneous, isotropic and timeless. To explain the observed redshift of distant galaxies in such a steady-state universe, which appeared to increase in proportion to their distance (Hubble's law), Swiss astronomer Fritz Zwicky, proposed the tired light theory in 1929.

New information

While some Hubble Space Telescope observations did point towards the impossible early galaxy problem, it was not until the launch of JWST in December 2021, and the data it provided since mid-2022, that this problem was firmly established.

To defend the standard big-bang model, astronomers have tried to resolve the problem by compressing the timeline for forming massive stars and primordial black holes accreting mass at unphysically high rates.

However, a consensus is developing towards new physics to explain these JWST observations.

This article is republished from The CONVERSATION under a Creative Commons license. Read the original article.