Inspired by the JWST images, could such a telescope be theoretically be made? I recall College physics that said the universe was opaque for the first few hundred thousands years post Big Bang so, I would have thought, no.
Here’s what Wikipedia has to say about this:
In other words, for the first 370,000 years, the universe was opaque, so we cannot see light from then. The earliest light we can see comes from when atoms began to form, but this light is so redshifted* that it appears to us as microwaves, not visible light (hence Cosmic Microwave Background Radiation, CMBR). This “light” is absolutely everywhere.
After that it took some time for the newly formed atoms to collapse into stars where fusion can happen, so while the universe is transparent there isn’t really any light for us to look at.
Once stars and galaxies form the light from them does travel here, so in terms of pulling up a telescope and looking far enough out and back to see the early universe, that’s the best we can do (other than the CMBR).
*Redshifting is caused by the expansion of the universe WITHIN a wave. If a wave has a wavelength of X, but the space the wave takes up becomes bigger because the universe is expanding, the wave becomes bigger; the type of light is determined by the length of the wave, so if the wave is stretched out, the type of light (or electromagnetic radiation, since we’re out of the visible light range here) will change, from red light to infrared to microwaves (and, in the distant future, the CMBR will be redshifted even further, into radio waves).
And “opacity” depends on what you’re looking at. Before recombination, it was opaque to pretty much all wavelengths of light, but light of various wavelengths isn’t the only option. Neutrinos can penetrate things that light can’t, so that lets you see earlier… but surprisingly not all that much earlier, perhaps to 200,000 years. The next step past that, though, is gravitational waves, and a suitable gravitational wave observatory could detect all the way back to a tiny fraction of a second (just how tiny a fraction of a second would be one of the myriad questions such an observatory would answer).
Preliminary designs do exist for a gravitational-wave instrument that could do this, but it’d be about two or three generations more advanced than LISA, which is itself still in the “Cross your fingers and hope it launches someday” stage.
And if you’re wondering what gravity waves they would be detecting before anything had coalesced, it’s early quantum fluctuations, which (weirdly) should be detectable - and with technology that’s not too far away. As in - something I hope to see within my lifetime.
Potentially maybe, but from what I know on the topic, I don’t think that method can work. They’re counting on being able to subtract out all of the foreground in order to see the cosmological background, but at least in the wavelength range of ground-based detectors, there are potential combinations of foreground objects that could exactly mimic the background, and so you can never be sure if you’ve subtracted away all of the foreground.
The meaning of the words “transparent” and “opaque”, in this context, are unclear to me.
In my experience, these words refer to whether light is able to pass through something. If they can pass through, the object is transparent; if not, it is opaque. But in this context you seem to be talking about the creation of new photons, and the opacity results from the lack of any light source at all. And then, at age 370,000, it’s NOT the case that one could see through stuff, but rather that one could see the stuff itself.
Am I close?
The opacity comes from the fact that a photon could not go very far (comparatively) before it encountered a charged particle and was absorbed.
There was plenty of light source, as the gas was emitting light, it just didn’t go far.
Think of it as a red hot frying pan. It’s emitting light, but the only thing you can actually see is the surface.
We see the CMB as being emitted at exactly the temperature at which hydrogen is ionized, as as soon as it dropped below that temperature, the universe was no longer opaque. Then it red-shifted to microwaves from there.
No, “transparent” and “opaque” have their usual meanings, here. Both before and after recombination, photons were continually being created. But before recombination, any photons that were created didn’t get very far before being absorbed again. After recombination, all of a sudden, whatever photons were created could continue on forever, or nearly so.
Thank you both!
The Sun is an almost perfect analogy. In the interior, photons are constantly emitted but then immediately reabsorbed, so the Sun is opaque. We see only the surface of the Sun, from where emitted photons can travel toward us through transparent space unimpeded.
https://image.gsfc.nasa.gov/poetry/ask/a11354.html
The surface of the Sun is analogous to the surface of last scattering that we “see” as the CMBR. The remaining conceptual difficulty is that this “surface” of last scattering was defined by a change in conditions through time (with temperature falling and conditions changing everywhere) rather than a change in conditions across space like the interior vs the surface of the Sun. So the surface of last scattering occurred at a specific moment in time everywhere simultaneously.
Actually, I should correct myself, here:
Before recombination, photons were continually created. After recombination, far, far fewer photons were created, until the birth of the first stars. This is precisely because of the transparency: Things are equally good at absorbing and emitting light, so something that’s not absorbing much won’t emit much, either.
I think I asked this in some way before, in response to a post.
Really big long base gravitational wave detector.
I think about all the highly accurate atomic clocks we have out there on the GPS satellites at various orbit heights. Geostationary and otherwise. Always relaying their timing to earth bases with atomic clocks. Would a gravitational wave cause detectable shifts in the clock times? Not talking about measuring some apparent position shift, but a timing shift. I have no idea if the frequency of sampling and comparing of the timing signals is capable of discerning such a shift and triangulating the source point.
Maybe it is not in place due to being of no practical use. But maybe bases dedicated to it, with the required discrimination can be built?
Or am I just incorrect in the basic concept that it could detect waves?
To elaborate on my maybe worthless idea.
As a gravity wave crosses the array of satellites, each one in the wave will experience a different time frame. Gravity influencing the time passage relative to another place in a different gravity situation.
So a clock will experience a slower or faster time rate in the wave. Knowing the position of the satellites and noting when and by how much their timing shifted may show direction and intensity of a wave?
By the same token, even today photons generated by a couple hydrogen atoms fusing at the core of the sun takes 100,000 years to get to the surface whereupon they fly in eight minutes all the way to Earth.
This is a good thing because on the way they get transformed from gamma rays to the more visible light we prefer.
In principle, yes. But in practice, using any existing set of man-made satellites, it’d require ludicrous levels of precision, far, far beyond anything plausible for what we have.
On the other hand, if you use really long baselines, it becomes plausible. One technique for searching for gravitational waves (which I don’t think has yet been successful, but which looks promising) is pulsar timing: You look at a whole bunch of pulsars, all of them many lightyears from Earth, and look for patterns in the timing of the pulses from them, from extremely low-frequency gravitational waves passing through the space between us and them.
…and presumably we’ll never be able to see the moment of the big bang, even ignoring the period the Universe was opaque, due to the limitations of Planck time which means we could only see back to 10−44 seconds?
It’s not even clear that there was a “moment of the big bang”. Currently, one of the most promising models is what’s called “eternal inflation”: Basically, the idea is that inflation goes on forever. It’s unstable, so every so often a bit of it collapses, but those collapsed bits can only expand at the speed of light, and more inflationary space is continually created faster than those non-inflationary bubbles can grow, so there’s always inflation going on continually, somewhere.
If this model is correct, then even if we had the physics to fully comprehend what’s going on during inflation, and the as-yet undreamt-of instruments (because we’d need that physics to dream them up) to probe back deeper into the inflationary era, we’d still never get back to The Beginning, because there was no beginning (or rather, the point in time which could most reasonably be described as “The Beginning” would be when our particular pocket of non-inflation started collapsing).
LIGO detects gravitational waves by detecting a change in the mirrors’ distance of 1/10,000 a proton diameter, which I found pretty impressive. I suspect though, trying to detect one through time shifts would be several orders of magnitude higher.
Unfrotunately we cannot see the big bang even in theory. Viewing the big bang would mean seeing to the particle horizon whch is the boundary of the observable Universe, but unfortunately redshift diverges at this biundary. However we can, ignoring the opacity of the early Universe and other such trifling problems, see arbitarily close to the big bang.
What I find an interesting coincidence is that that distance is also, to within an order of magnitude, the measured upper bound on the diameter of the electron. Those two are the top contenders for “smallest distance ever measured”, using completely unrelated technologies, and they’re almost exactly the same.