“The Doppler red-shift of light observed from distant stars and galaxies gives evidence that the universe is expanding (moving away from a central point)”. This sentence sort of justifies The BigBang Theory. If there were not such a thing (a great explosion), can we explain red-shift and blue-shift with circular motion of galaxies? Why blue-shift, anyway? If there was one explosion, how can some rocks be accelerating towards us?
Galaxies are still gravitationally attracted to each other, so when they’re close by they may still be moving towards us. Far away, though, they’re inevitably moving away rapidly, because the rate is roughly proportional to distance. Galactic motion is only a small modifier on top of that.
Circular motion can’t account for this observation. Aside from a giant and unlikely coincidence, there’s not much to explain the Hubble constant except for the metric expansion of space. It’s not an explosion so much as it is that there’s a constantly increasing amount of space between any two objects.
Redshift and blueshift are not exactly literal. “Red” just means toward lower frequencies, and blue means toward higher frequencies. It depends on your starting point, and it’s only literally red or blue when the starting point is roughly white and the amount is not too much. Very distant galaxies get redshifted down to radio waves. Extreme blueshifted things (like the jets emitted by some black holes) might really be in the gamma ray range.
(Many years ago, if asked about the color of the fancy sports car that my aunt then owned, I used to reply “the way my aunt drives it, it’s blue in the front and red in the back.”)
The Big Bang, despite its name, was not an explosion. Fiurthermore, there’s no point that it’s expanding out from. (These are probably the most common misunderstandings about the BB.) The BB is an expansion of space, the entire universe, which started off as an extremely small volume, infinitesimal in fact. Think of it as more space coming into being in between all the galaxy clusters.
As far as blue-shifted galaxies, there’s only a very small number relative to the total number of galaies in the universe. They’re mostly in the Local Group, but I believe a few in other nearby clusters. Everything else in the universe is redshifted.
I don’t think any galaxies get redshifted to that extreme. The Cosmological Background Radiation was initially emitted in the UV and is now in the radio part of the spectrum. But that has a redshift z > 1000. Distant galaxies have a redshift z of around 10 or 12. That will shift their light, which was initially bluish, into the infrared. Which is why JWST is mostly an infrared telescope. It was intended to see those galaxies.
It’s worth mentioning that the JWST’s operation in the infrared also allows it to penetrate clouds of dust and gas that are relatively opaque to the higher frequencies of visible light.
There is no central point. The Big Bang was not an explosion in space - it was the creation of space (actually, space-time).
The classic analogy here is to imagine a balloon that starts out infinitely small, then expands to a huge size. Which point on the expanded balloon’s surface is the center of that surface?
Or, the starting point was here. No matter where you go, the starting point is always where you are.
Perhaps it’s more of an omniplosion?
Yes - because all points in space were once infinitely close together, every one of them has an equal claim to be the center.
I like that word.
Good catch–you’re right. I had to look up a chart to see where the radio/IR threshold is, and it was surprisingly far down–300 GHz. The CMB itself is not too far from this at 160 GHz.
There may be early stars with redshifts greater than the early galaxies, but they still wouldn’t be quite at radio range. Though 300 GHz is of course an arbitrary threshold; it’s all EM waves in the end.
It took a fairly long time after the CMB (“the surface of last scattering”) to when the first structures could have formed. So there’s a pretty big observational gap when the radio/IR transition actually happened.
Note that the redshift parameter z is not linear with respect time. A z ~ 1 is half way back to the Big Bang, while the CMB has a z > 1000 (I’ve heard different numbers for it, but all between 1000 and 1100). I don’t keep track of what galaxy or other object has the highest measured z, but somewhere around 11 to 13. No doubt JWST will break whatever the pre-JWST record is, if it hasn’t already.
13.20 according to April findings.
The OP puts the sentence “The Doppler red-shift of light observed from distant stars and galaxies gives evidence that the universe is expanding (moving away from a central point)”. into quotes. Goggling brings up several sites that include the sentence, all of which appear to be sincere attempts to explain the Big Bang.
That’s too bad, since it’s not just wrong but grossly misleading, as others have said. Unless you already know that it’s wrong, there’s no good warning that you’re going down a bad path. It’s why some people blanketly condemn the internet. They shouldn’t: books probably have similar ratios of bad information to good. Nevertheless, the problem is real.
Additional question.
Recently I planned (to do, but did not) a conversion program from technical drawing to G-code. In CNC machining you have straight paths (or line segments) G0/G1 and arcs G2/G3. Those commands have different number of parameters and I was tempted to cut corners and use arc-command (using ridiculously long Radius) to replace linear movement.
Now, In physics everything seems to be revolving - is linear movement a real thing or could it be just circular movement in riculously short time period? Let’s take a hard example - gravitation. It seems straight, but if you follow two planetary objects for a few days where are the straight forces…
The straight forces are towards the other object. And I’m not even sure what it would mean to have non-straight forces… Forces are vectors, not paths.