Science Saturday Open Thread: Doppler Effect

 17 replies

Tony does his best to make you smarter, despite the comments section.

This is a guest post by Leaf.

Once upon a time, our illustrious scientific guru deemed to explain the size of the universe. The numbers used to describe the sizes and distances seen in the universe are mind-blowingly ridiculous and are frankly hard to fully comprehend their sheer enormity. That’s a lot of words just to say it’s fucking huge. What if I blow your mind and tell you it’s not only huge, but it’s getting bigger? Now let me blow your mind a second time and tell you that not only is it expanding, it’s speeding up. Let that sink in for a moment. This mind-numbingly huge universe is get bigger, and not only is it getting bigger but the rate at which it is getting bigger is getting faster. 

Now there are many ways I can take this topic, all of which are extremely fascinating. For this I’m going to focus on how we know what we know. You might remember awhile back our esteemed scientific virtuoso talked about spectroscopy. You’ll remember he mentioned that different elements absorb/emit different wavelengths of light and that they leave marks in the light spectrum, like a barcode. Scientists can use these spectral lines to determine the makeup of distant stars. An interesting nugget is the lines from a distant star don’t quite line up with the way they look here on Earth. The patterns are the same, but their location on the light spectrum has shifted. 

Another tidbit our renowned scientific expert recently mentioned (I’m not very original here am I) was that light is a wave. When the source of a wave is moving the waves in front of it are compressed while the waves behind the source get stretched. This is called the Doppler effect. A good real world example of this is a vehicle will sound higher pitched as it is approaching you, but once it passes you the sound gets lower as it moves farther away. 

When it comes to the light spectrum, blue light has a shorter wave length and red light has a longer wavelength. Therefore compressed light waves will appear more blue, while stretched light will appear more red. This is called blueshift and redshift. If something is blueshifted, it is moving toward you. If it is redshifted, it is moving away from you. 

So how does this prove the universe is expanding? As far back s as the late 1840s scientists were attributing the shift in the observed special lines of distant stars to the Doppler effect. But it wasn’t until 1929 that Edwin Hubble measured the redshift in 46 galaxies discovering that galaxies where moving farther away at a rate proportional to their distance (meaning the farther away they were the faster they were moving). This is strong evidence to support the idea of the Big Bang. In an explosion, material around the outer edge of the source will travel the farthest and the fastest. But eventually the energy from the explosion dissipates that material will slow down its rate of travel due to counteracting forces. So one would think that the expansion of the universe would follow that same logic as gravity pulls everything back. At the very least, there is no counteracting force and everything just continues on at the rate they currently are going on into infinity, right? Well in 1998, two separate teams researching supernova used the redshift to compare the the rate of expansion since the supernova occurred. They discovered that it’s extremely likely that the universe is speeding up in its expansion. “How is that possible”, you might ask. That my friends is a topic for another Science Saturday.   

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larch
larch
05/23/2020 1:19 pm

Off topic but this hummingbird drone filming monarch butterflies is stunning:
https://www.youtube.com/watch?v=lWOySU_hAz0

zulu trader
zulu trader
Reply to  larch
05/23/2020 1:23 pm

amazing

BleedingRedAndGold
Reply to  larch
05/23/2020 1:54 pm

Looked like science to me. What I find even more interesting is that monarch migrations span generations, so there’s zero chance of any of them remembering the route in either direction. The monarchs from Canada didn’t pupate there, their ancestors did.

MasterChief
MasterChief
Reply to  larch
05/23/2020 4:36 pm

Terrifying if not for the beautiful wings.

BleedingRedAndGold
Reply to  MasterChief
05/23/2020 4:45 pm

Monarchs are really interesting. Can’t recall if they only lay their eggs on milkweeds, IIRC feeding on them’s what makes their caterpillars poisonous, and I believe some of the toxin stays in the adults, thus the distinctive wing patterns. IIRC there’s another butterfly that mimics the pattern without having any toxins of its own for the protection it gets by doing so.

All that said, I’m fairly sure there are insectivores who can eat a monarch or two without much difficulty, but there’d be a point where it would have to stop eating them until its system clears up. I imagine a critter who eats too many of them and survives it won’t be too eager to consume more.

MasterChief
MasterChief
Reply to  BleedingRedAndGold
05/23/2020 6:12 pm

Late last winter her in CA we had a hug butterfly migration. We decided not to drive around for a couple days because we were smashing so many driving down the road. They weren’t monarchs but they were cool. They came right off the hills behind my house and swept down into the valleys. It was cool to see.

BleedingRedAndGold
05/23/2020 1:16 pm

“How is this possible?” Well, I have a half-assed notion about that, not even up to the hypothesis level, but… You see, a while back I came across the actual quantum physics idea that right down at the bottom of everything matter’s composed of moving quantum fields, and that got me to thinking.

The common understanding of spacetime is that movement is something that happens within space and time, but what if that’s backwards and it’s movement that creates spacetime? The implications of that are considerable, but one interesting one is mathematical and related to the heat death of the universe. You see, if spacetime’s created by movement, what happens when the last stuff stops moving? What if space and time collapse, then what? Mass-energy can’t be created or destroyed, so all the quantum “residue” is still there, it’s just evened out, so if spacetime collapsed down to a mathematical point, would the sudden, massive compression of everything create another Big Bang?

The math’s far beyond me to go father with the notion, but it would account for some stuff, it seems to me.

WaywerdSon
WaywerdSon
Reply to  BleedingRedAndGold
05/23/2020 2:00 pm

It boils down to the total amount of mass in the universe, and we dont really know that figure. We know there is WAY more than we can account for visually, but if there is enough to overcome the expansion and cause a “big crunch” is unknown. The universe will end one of 2 ways, it will either expand until there is so much distance between atoms that nothing can happen and it just peters out, or it collapses into itself and creates a new singularity. Either way, I probably wont be around to see it

BleedingRedAndGold
Reply to  WaywerdSon
05/23/2020 4:05 pm

I’m familiar with that theory, but it follows the standard assumptions of movement being a byproduct of spacetime, what I’m talking about is kind of the opposite of that, that spacetime’s a byproduct of movement. Furthermore I’m talking about when the last quantum field stops moving and there are no atoms and thus no mass or gravity.

At that point, if spacetime’s a byproduct of movement then spacetime would collapse in on itself because there’s no more movement. No more spacetime, all that quantum residue sitting perfectly still becomes a single point again. Granted that I’m idealizing this because I have difficulty believing that a single moving quantum field would support all that space by itself and my expectation that there would be a tipping point involved, but I can’t nerd that well or math that hard to figure it out.

BleedingRedAndGold
Reply to  BleedingRedAndGold
05/23/2020 4:33 pm

And as best as I can figure it would be compatible with the general relativity model, which tells us that velocity affects time just as mass affects space. That’s proven out by the fact that GPS satellites have to correct for the duration difference caused by their velocity. Anyway, if everything that exists comes down to quantum fields in motion and those collective quantum fields affect both space and time by existing and moving then postulating that movement produces spacetime it isn’t much of a stretch.

Of course, this all depends on whether or not the absolute bottom layer of reality actually is just a matter of moving quantum fields. I think. Maybe. But I see no reason at this time to junk it as too bizarre to be true. Physics and its Quantum subset are full of things that are bizarre and counter-intuitive, after all.

vvet818
05/23/2020 10:24 am

If it is redshifted, it is moving away from you.

https://youtu.be/QiaGSz9LQJE

I can understand that.

BleedingRedAndGold
Reply to  vvet818
05/23/2020 1:43 pm

Fun fact, cheetahs can’t run for extended periods, and if one tried it could kill itself from overheating. Good thing our Cheetah only has two legs, right?

zulu trader
zulu trader
05/23/2020 9:46 am

Yeah, but what does the Bible say about it?

Jeremiah 10:12
It is he who made the earth by His power, who established the world by His wisdom, and by His understanding stretched out the heavens.

x

https://giphy.com/gifs/animation-space-explosion-l41JS0g6UPOoKV7Z6

fishbowl72
Reply to  zulu trader
05/23/2020 10:09 am

Jesus this, Moses that, Abraham hit me with a wiffleball bat…

probablyamistake
probablyamistake
Reply to  fishbowl72
05/23/2020 12:38 pm

You should have ducked.

fishbowl72
05/23/2020 9:40 am

I just learned that George Lindsey, the actor who played Goober, was Gene Roddenberry’s first choice to play Spock. He was also a high school science teacher. Doppler THAT.

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