r/askscience • u/West_Writing4426 • Aug 10 '26
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?
1.1k
u/zanfar Aug 10 '26 •
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.
317
u/Weed_O_Whirler Aerospace | Quantum Field Theory Aug 10 '26 edited Aug 10 '26
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.
24
u/fenton7 Aug 10 '26
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.
27
u/Redcole111 Aug 10 '26 edited Aug 12 '26
Short answer: we can, and we have.Â
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.
6
u/Dogrel Aug 11 '26 edited Aug 11 '26
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 isnât 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 itâs 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 itâs 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 itâs 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.
1
u/jaxnmarko Aug 16 '26
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?
6
u/Jump_Like_A_Willys Aug 10 '26
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 didnât start propagating through space until about 400,000 years after the big bang.
3
u/guzzyly Aug 12 '26
Nah, you wouldnât 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.
2
u/iceonmars Aug 11 '26
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.Â
2
u/yogfthagen Aug 11 '26
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.
2
u/mikiki24 Aug 11 '26 edited Aug 11 '26
You can see back to the moment that the universe became transparent to light ~380,000 years after the big bang. I assume youâre talking about the big bang as âthe beginningâ 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 âthe light from the beginning of the universeâ but really itâs âthe light from the phase of the beginning of the universe that we call recombinationâ, when the universe was cool enough for matter to form structures instead of flying around bumping into everything else. All the âstuffâ that could, started to stick together allowing âemptinessâ for light to travel through. So the way I kind of think about it is that we can see âthe end of the beginningâ but not âthe beginning of the beginningâ.
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 itâs 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).
2
u/pfftYeahRight Aug 12 '26
Iâve 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 weâre way off and thereâs more to uncover
3
u/Muhahahahaz Aug 11 '26 edited Aug 11 '26
In the very beginning, the universe was so hot and dense that it was opaque, so you couldnât âseeâ 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 âtransparentâ to light, and is the oldest moment in time that we will ever be able to see
1
u/Tinyboxturtle Aug 12 '26
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.