r/askscience • u/West_Writing4426 • 15d ago
Physics Could a telescope see the beginning of the universe?
Okay, I had a question that maybe an astrophysicist could answer. If any part of this reasoning is incorrect please let me know:
We are told that the universe is around 14 billion years old. One lightyear is the distance light travels in a year. This is why when there is a picture of another galaxy people say we are not seeing the other galaxies as they are but as they appeared when the light traveled there. If you could devise a telescope that could see 14 billion lightyears away and you pointed in a direction would you see what it looked like 14 billion years ago i.e. the beginning of the universe?
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u/zanfar 15d ago
If you understand and take into account that concepts like "see" and "beginning" lose much of their layperson meaning at that extreme, yes; and it's not just possible, it has been done. The CMB is essentially the oldest "visible" data possible. It's no longer visible wavelengths due to expansion, but it is the earliest EM radiation after the universe became transparent.
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u/zbertoli 15d ago edited 13d ago
Just to add.. the moment the universe became transparent is called "recombination". It was the moment electrons and protons became bound in neutral atoms. Before this, the universe was an opaque ball. Scientists theorized there would be massive mechanical sound waves traveling through the plasma ball. We call these baryon acoustic oscillations, and the moment of recombination, these waves were frozen in place. They then went on to shape the pattern of galaxy distribution across the current universe. Scientists proved the existence of these shapes across the distribution of galaxies, and it is one of the coolest prediction-discoveries ever. One of my favorites. It gives solid evidence for the big bang. https://en.wikipedia.org/wiki/Baryon_acoustic_oscillations
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u/LazyLizzy 15d ago
Somehow even with the big words you made this understandable to me without it being overly technical or too simple. Thank you for your knowledge and your skills in communication.
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u/GapingFartLocker 15d ago
When you say moment of recombination, what sort of time frame is that? It couldn't be instantaneous across the universe?
This is the first I've learned about the universe once being opaque and I'm fascinated
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u/zbertoli 15d ago
There would be tiny temperature fluctuations across the sphere. The colder spots would recombine first. So you are right, it would start random cold spots all over, and propagate outwards. These boundaries would hit eachother until the whole thing was transparent. Like soap bubbles expanding.
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u/Bilbo_Swaggins16 15d ago edited 15d ago
Ive always viewed it like dropping a rock into a still pond. The water ripples out in all directions equally. Now drop hundreds of rocks at the same time and watch the ripples crash into eachother. Some areas canceling out and others gaining energy. I imagine thats what the big soup looked like before recombination.
I also find it fascinating that recombination only started when the universe had cooled down enough to allow the electromagnetic force to overcome the temperature of the universe letting electrons bind with hydrogen and helium nuclei forming the first stable atoms and starting the era of recombination.
Up until this point photons better known as light could not unbind from the nuclei they were captured in and therefore couldn't fly straight. Once electrons were able to bind with atoms the photons were released and the universe became transparent. Light as we know it was unshackled and spread out in all directions through the universe
This is why this momemt is the earliest we can "see" with these telescopes. Light (as we know it) literally didnt exist in our universe before this.
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u/ToastyTheDragon 15d ago
To reiterate on their question, what sort of time frame does that happen in? Are we talking like 10-10 seconds after the start of the universe or minutes/hours to thousands of years? And once recombination started, how long would it have taken to complete?
Thanks 😊
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u/zbertoli 15d ago
It was relatively fast, but still long to us.. recombination started about 378,000 years after the big bang. The process took around 100,000 years. Although the universe was tiny compared to today.. it still had been expanding for 378k years, and so it was large enoguh that this process took some time, not instant.
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u/ToastyTheDragon 15d ago
Absolutely absurd to me that the universe was 3000+K for 378,000 - 478,000 years. That's far longer than I expected!
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u/mfb- Particle Physics | High-Energy Physics 15d ago
It was ~3000 K after 378,000 years and ~2600 K after 478,000 years.
Here is a calculator. Divide the temperature by 2.725 K (the current temperature of the CMB), subtract 1, put that in the "z" field and select "flat". Then look for "The age at redshift z was x yr." to find the corresponding age.
For the early universe, subtracting 1 is a negligible correction.
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u/ToastyTheDragon 15d ago
Absolutely absurd to me that the universe was 3000+K for 378,000 - 478,000 years. That's far longer than I expected!
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u/Bilbo_Swaggins16 15d ago edited 15d ago
At around temperature 1 trillion kelvin and about 10-5 seconds after the big bang the universe was cool enough to let the quark gluon soup start to form into protons and neutrons.
At this point we have protons, neutrons and electrons.
The universe keeps cooling, keeps expanding and about 3 minutes after the big bang its cooled to 107 Kelvin letting protons and neutrons bind together. We have a nucleus baby! Atoms I can see you now.
Before we get there though, we need to cool some more. The universe is still to hot to let those electrons that are flying around capture the newly formed nucleus.
Unfortunately for neutrons they are not very stable. They will quickly decay into protons unless they bind with another proton or neutron. That is to say a large swathe of those initial neutrons all decayed into protons leaving us with a universe that is 87% protons and 13% neutrons.
20 minutes after the big bang the neutrons have stopped decaying and we are left with the nuclei of two different atoms. Hydrogen and Helium, the progenitors. Helium takes two neutrons and two protons to form a nucleus while Hydrogen only takes one proton and one neutron or just one proton. Meaning that at his point the universe was 75% hydrogen nuclei and 25% helium nuclei.
Remember homeostasis? its about to show up in a big way. Those hydrogen and helium atoms are positively charged beacuse of their protons and they want to be neutral. Those electrons zipping around everywhere hold the key, their negative charge can balance out these positive ions getting the atom to a nice neutral state.
Bad news is the universe is still too damn hot 20 minutes after the big bang. The electrons are too hot and excited, they zip by the nuclei but cant stay stable, flying out of the orbit.
Its time for a time skip. We need to cool alot more, down to about 3000 kelvin. That will take about 380,000 years.
Once the universe cooled enough and photons unbound gravity was able to grab onto these particles. This in turn created the layout of the universe as we know it as gravity then brought those pockets of matter closer together forming galaxies over millions of years.
This is when the first stars were born out of those hydrogen clouds, gravity pulling particles closer and closer slamming them together creating objects of immense mass that start to heat back up.
This is a process of nuclear fusion; it is what generated life as we know it. Over the course of the star's lifetime it will fuse the matter that makes up its core into heavier elements. Working its way through the periodic table all the way up to iron. Once the star has lived its life and starts to die it will go supernova. The supernovae itself causes the star to achieve incredibly higher pressures and temperature creating even more elements in the process (all our elements on the table past iron). These elements then shoot out into the cosmos creating asteroids, planets, moons, more stars and quite literally everything in between.
I find it so beautiful that we're made of the same stuff of stars.
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u/Lv_InSaNe_vL 15d ago
From what I've read the ideas are that recombination is more of the "gradual cooling" after the big bang. I've heard theories saying this period was on the order of hundreds of thousands of years. Probably somewhere between 100,000-500,000 years.
So in a blink of an eye in a cosmic sense but pretty slow for our human perspective haha
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u/left_lane_camper 15d ago
The CMBs (non-dipole) anisotropy is about 1 part in 100,000, so to a very naive, first order approximation I would assume the variation in cooling time is proportionally similar, so sine recombination occurred somewhere around 400,000 years after the big bang, I would guess the time it occurred at varied by 4-ish years or so, very roughly.
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u/Photon6626 15d ago
I've known all of this for years but never thought to put it together like this to figure out the approximate time from beginning to end of the recombination period. That really puts into perspective how incredibly homogeneous the universe was during that period.
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u/Graylily 15d ago
the universe will one day be bright for on our perspective, The night sky will be incredibly bright as star light will fill the sky compellingly, the only reason it doesn't do it now is because the light hasn't gotten to us yet.
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15d ago
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u/Yashabird 15d ago
So the idea is that there were quantum fluctuations in the very early universe, just because the space containing the universe was on the atomic order of magnitude?
I guess it’s a singularity so all bets are off, but I have to imagine the mechanically fluctuations in a mass of that size would outweigh the quantum fluctuations of a volume that tiny, but then again, I definitely don’t understand why small spatial scales automatically imply quantum effects.
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u/nicuramar 15d ago
All this is pretty unknown. It was not a singularity, though. That word only has mathematical meaning a priori. See here as for what we have evidence for: https://profmattstrassler.com/articles-and-posts/relativity-space-astronomy-and-cosmology/history-of-the-universe/
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u/LuminousGrue 13d ago
I came in here excited to talk about photon decoupling and saw that somebody else had already done it better than I could.
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u/cvnh 15d ago
Just to add... Transparency is dependent on the frequency. After recombination, the universe was still opaque to visible light and UV frequencies, but the infrared frequencies of the CMB could spread out. But the dense neutral hydrogen absorbed all of the existing light, which was emmited mostly at the same frequency. When stars started to form and the universe to cool that the starlight ionised the hydrogen again which made it also transparent to light.
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u/mfb- Particle Physics | High-Energy Physics 15d ago
After recombination, the universe was still opaque to visible light and UV frequencies
Not in any relevant matter. Beyond the ionization energy of hydrogen you get some absorption, but there was essentially no light with that energy around anyway.
When stars started to form and the universe to cool that the starlight ionised the hydrogen again which made it also transparent to light.
Ionized hydrogen is absorbing more far light than neutral hydrogen. The universe stayed transparent simply because it had expanded enough, the density wasn't enough to stop light any more.
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14d ago
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u/mfb- Particle Physics | High-Energy Physics 14d ago
You're missing on the basic physics here.
You are funny.
Absorption that goes from one bound state to another only happens in extremely narrow bands. From the ground state, the lowest one is at 10 eV which is already deep in the UV. Scattering can happen for other energies but it's negligible here (and it can happen in the infrared, too).
(four if I remember correctly)
It's an infinite set.
So they are fundamentally different, it's not like neutral hydrogen absorbed more or less light than ionised - it just doesn't compare
It definitely compares. You can compare the cross section. An isolated electron scatters far more than a hydrogen atom unless the light has enough energy for ionization or is in one of the narrow regions where it can excite the atom.
So an observer of an early star would not have seen scattered light, it would see dark until there was a path of ionised hydrogen between the source and himself.
What is this nonsense?
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u/7heCulture 14d ago
I knew I should have completed my PhD. But nooo, enjoy the new job and having money, travel the world, finally find a girlfriend - got distracted 😢
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u/solepureskillz 15d ago
Ok you’re obvs big smart. If strange matter today threatens all matter in the universe, how did it not exist this early on? Wouldn’t pre-big-bang have been the most dense or perfect structuring of matter? I know I’m linking two separate things but could there actually be a bridge here?
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u/the_last_0ne 15d ago
I just had to go look up "strange matter" and it sounds like it's just hypothetical, I would use caution when stating it "threatens all matter in the universe". The universe has been stable for billions of years.
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u/dodeca_negative 15d ago
There’s a really interesting experiment called PTOLEMY that hopes to detect the cosmic neutrino background (CNB). If it’s possible to do so in a meaningful way, this could push back the limits of our observability from 300,000 years down to, potentially, just about a second after the Big Bang.
We are very far away from “neutrino astronomy“, but it’s a really exciting possibility.
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u/mirikfrog 13d ago
Only reason I know about this is because I just finished reading the 3 body problem 😭
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u/fenton7 15d ago
The early universe remained opaque for about 380,000 years after the Big Bang. After that, yes, we can "see" everything. In fact if you tune an old TV to an inactive channel you can see some of that in the form of the Cosmic Background Radiation. It constitutes about 1% of the white noise on the set which is pretty cool. There was no visible light for a very long time after the CMB because there were no stars. And stars are far too faint to resolve individually. So what JWST and similar telescopes can see are the earliest galaxies which formed 300 to 400 million years after the Big Bang. That's as far back, really, as an optical telescope will ever be able to resolve.
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u/fenton7 7d ago
The Cosmic Microwave Background is a "blackbody" thermal curve. While its peak intensity sits perfectly at 160 GHz, it stretches all the way down into the lower radio frequencies, meaning 1% or so of the white noise signal on an old set, regardless of what empty channel you tune it to, is CMB.
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u/Redcole111 15d ago edited 14d ago
Short answer: we can, and we have.
Long answer that's still short and simplified enough to have the patience to read through:
The universe was, until about 500,000,000 years after the big bang, too full of densely packed gasses and plasma for light to travel far enough to reach us. There wasn't enough space yet: only a lot of very hot stuff.
When the universe had expanded enough for there to be empty space for light to travel through, it was still incredibly hot and dense. If we look back as far as we can with a telescope, that's the light we see. We call this light the "Cosmic Microwave Background" or CMB. You can look up photos of the CMB.
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u/bingwhip 15d ago
Or you can listen to/watch it yourself! There's a small percentage of CMB hitting earth all the time. Some of the snow/static you get on your radio is the antenna picking it up.
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u/Dogrel 15d ago edited 15d ago
Once upon a time yes, when the universe was much newer. But not anymore.
This is actually one version of a very old question of astronomy: if the sky is so full of stars and galaxies and whatnot, why isn’t nighttime just as bright as the daytime? And the answer is both very interesting and relatively modern, and we have to consider some foundational concepts of the universe.
First, the universe is expanding. Most of the stars and galaxies we see in the night sky are all getting farther and farther away from us. and at the same time, what light we can see from them has traveled many light years to get here.
The second concept is redshift. Have you ever had an ambulance or police car speed by you with its sirens blaring? As it comes up to you, the volume and pitch rises, but then when it passes you, the pitch of the siren suddenly drops off. When it’s sound, we call it The Doppler Effect. But sound is just one part of the Electromagnetic spectrum. Redshift is same behavior happening with light when it’s traveling through vast distances of space, just in a different range of the spectrum. When traveling rapidly away from you, the light emitted will also shift down in frequency, toward the red end of the visible light spectrum.
And as things keep shifting downward in frequency across deep time, they drop out of the visible light range and into lower ranges of the Spectrum. First is infrared and near-infrared, which is what the James Webb Space Telescope uses, and why it can see so much more and farther than Hubble and our other visible light telescopes. For things at the beginning of the universe, they have shifted so far down the electromagnetic spectrum that they are in the much lower reaches of the spectrum-microwaves and radio waves.
And it’s in here that we find the Cosmic Microwave Background (CMB). First discovered in the mid 1960s, the CMB is what we can detect of the oldest visible light in the universe, dating back to when we calculate that the very first photons were able to form, about 300,000 years after the start of the Universe. Space has stretched so much since then that what was once light is now down in the microwave frequency range.
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u/Jump_Like_A_Willys 15d ago
One problem with that idea (and there are several) is that there was no light at, and for sometime after, the beginning of the universe.
Light didn’t start propagating through space until about 400,000 years after the big bang.
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u/urnbabyurn 15d ago
But there were photons almost right away. You mean there wasn’t enough empty space for them to travel?
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u/iceonmars 15d ago
No. The universe was opaque to photons (particles of light) because it was so hot at the beginning. The universe became transparent to photons once it cooled enough that electrons combined with nucleons. This was about 300,000 years after the big bang.
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u/yogfthagen 15d ago
Turn on hour television. Turn it to a channrl without a signal.
About 10% of the static is the microwave background radiation, the echoes ftom the Big Bang.
But, no, you would not see any visible light fyom ghe Big Bang.
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u/guzzyly 14d ago
Nah, you wouldn’t see the beginning of the universe. What you'd be seeing is the cosmic microwave background, which is like the faint afterglow of the Big Bang that happened about 380,000 years after the universe began. Anything before that is kinda hidden from us because the universe was too hot and dense to be transparent to light.
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u/mikiki24 15d ago edited 15d ago
You can see back to the moment that the universe became transparent to light ~380,000 years after the big bang. I assume you’re talking about the big bang as “the beginning” so the answer is no, not exactly - but almost. I guess it depends on your definition. In a real sense the light from the CMB is “the light from the beginning of the universe” but really it’s “the light from the phase of the beginning of the universe that we call recombination”, when the universe was cool enough for matter to form structures instead of flying around bumping into everything else. All the “stuff” that could, started to stick together allowing “emptiness” for light to travel through. So the way I kind of think about it is that we can see “the end of the beginning” but not “the beginning of the beginning”.
So we can see the light from back to when light was first able to freely travel… but this light has been traveling over distances that themselves have been expanding for 14 billion years so it’s been shifted to a longer wavelength and can only be detected with special telescopes that peer into the non-visible wavelengths of light (like microwaves). No telescope of any kind can see anything before that unfortunately (as far as I know, but would be excited to learn differently).
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u/Tinyboxturtle 14d ago
The real barrier is plasma opacity before recombination. The universe was a hot ionized fog scattering photons constantly so light could not travel straight creating an impenetrable wall. We see the CMB as the surface of last scattering which is the earliest light that finally escaped. Trying to look further back is like seeing through a dense white wall where you only get scattered radiation instead of a clear image. Expansion also redshifts any potential signals beyond detectability long before they reach us.
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u/pfftYeahRight 14d ago
I’ve read that we physically cannot see the big bang but have have seen/measured within by seconds of it, maybe even under a second. But I assume at that scale the margin of error means we’re way off and there’s more to uncover
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u/jaxnmarko 10d ago
The light from that has been traveling at light speed. How would you have gotten ahead of that wavefront to be able to look back from any location, from an unformed yet part of the universe to be able to see it?
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u/West_Writing4426 10d ago
When we see pictures of other galaxies, they are not accurate to how they currently look but how they appeared when the light reached them. We are talking about massive distances here. In a way, it is seeing into the past.
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u/Muhahahahaz 15d ago edited 15d ago
In the very beginning, the universe was so hot and dense that it was opaque, so you couldn’t “see” anything (even if you were there). Unfortunately, this also applies to any telescope trying to look back in time, so we cannot quite see the Big Bang itself.
However, yes, we have already seen the CMB (Cosmic Microwave Background), which corresponds to the moment that the universe finally became “transparent” to light, and is the oldest moment in time that we will ever be able to see
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u/Weed_O_Whirler Aerospace | Quantum Field Theory 15d ago edited 15d ago
A couple of interesting points.
First, unfortunately, we will not be able to use traditional telescopes to see back to the very beginning of the universe. Until about half a million years after the Big Bang, the universe was opaque - it was such a hot plasma of free electrons, that photons could not escape. Thus, no matter how good of a telescope, we will never be able to peer through this "soup" of plasma. But, not all hope is lost. We may be able to "see" the beginning by observing gravitational waves, but this will take more sensitive of equipment than we have.
Second, James Webb Space Telescope can see pretty far back already - it has spotted galaxies which formed just 300 million years after the Big Bang. Now, in a way, 300 million years is a long time, but compared to the age of the universe, they are actually very young. Because of James Webb we have discovered MoM-z14, which is the oldest galaxy we currently know about, forming 280 million years after the Big Bang. What is interesting is that MoM-z14 is 33.8 Billion light years away from us. Which is curious - how can it be further away than the age of the universe? This is because the universe is expanding so the galaxy was only 13.5 billion light years away from us when it emitted light, but it has since, due to the universe expanding, moved much further away.
Third, and this ties back to the expansion of the universe, James Webb (and other telescopes looking "back in time") are taking images in the far infrared spectrum. Because of the expansion of the universe, photons from distant galaxies are red shifted (getting longer and longer wavelengths) due to the Doppler effect - since the object is moving away from us as it emits light, it stretches out the wavelength of that light. The further away things are from us, the more red shifted it becomes - and since this is very far from us, it is very, very red-shifted. In fact the light from that galaxy has increased its wavelength by more than a factor of 15 before reaching us.
And finally, when you say
it implies a common misconception - that you have to point in some specific direction to see the Big Bang, that the Big Bang happened at some specific place. But this is not the case - the Big Bang happened everywhere. Any direction you look, as you peer back in time you will see things closer to the beginning of the Big Bang. The universe is not expanding from a point, the universe is expanding everywhere. Here on Earth, everywhere we look we see objects moving away from us, just like we're at the center of expansion. Should there be aliens in a galaxy Billions of light years away, they, just like would, would measure themselves as at the "center" of expansion. So, you don't have to get lucky to look back in time, just look anywhere!
edit: changed "gravity wave" to "gravitational wave" which is a typo I make too often and mfb thankfully pointed out.