The Universe has a Redshift and its Increasing

Super fact 79 : Distant galaxies appear redder (redshifted) because of the universe’s expansion. The farther away the galaxy, the redder it is. This cosmological redshift is also increasing because the Universe’s expansion is accelerating. Our Universe is getting more and more red every day.

Esther’s writing prompt: January 14 : Red

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Many people are aware that the Universe is expanding but may not know that this results in a measurable redshift. The faster a galaxy is moving away from us the redder it appears. This is called the cosmological redshift. Measuring these redshifts was how we discovered that our Universe is expanding.

Cosmological redshift vector illustration. Stretched and original space wavelength with earth and distant galaxy. Doppler effect astronomical phenomenon distance example. | The Universe has a Redshift and its Increasing
As the Universe expands and galaxies are moving away from each other the light will be stretched. Stretched light with longer wavelengths are more red. The phenomenon is called redshift. Shutterstock Asset id: 1180828402 by VectorMine.

At the end of the 1990’s it was also discovered that the Universe’s expansion was accelerating. This discovery came from measuring the redshifts (and apparent dimness) of distant Type Ia supernovae. I should add that measuring the increase in the cosmological redshift directly is difficult. However, it is expected to be possible when the Extremely Large Telescope (ELT) starts gathering data in 2027. I can add that there are also other types of evidence showing that the Universe’s expansion is accelerating.

Another surprising aspect is, if the Big Bang was like an explosion, gravity would pull back the galaxies making the expansion slow down and perhaps eventually even reverse. However, the opposite is happening. A common explanation is that a repulsive force, a sort of anti-gravity, referred to as dark energy, is responsible for this acceleration.

I call this a super fact because this is an observed phenomenon, it is important knowledge for how we view the world, and it is surprising. Many people have heard bits and pieces of this but do not have the fuller picture.

The Doppler Effect

The cosmological redshift is an example of the so called doppler effect. The doppler effect is the change in the frequency or wavelength of a wave in relation to an observer if the origin of the wave and the observer are moving compared to each other. If an object is moving towards you, let say an ambulance, the frequency of its sound will be higher (wavelength shorter).

After it passes you and moves away from the frequency will be lower (wavelength longer). In other words, the sound changes when the ambulance passes you. The same is true for other kinds of waves, including waves on the water, and light. If a light is travelling towards you at a high speed, it will look bluer. If a light is travelling away from you at a high speed it will look redder. The latter is what is called a redshift, cosmological redshift in our case.

The object is indicated by a red dot, and a red arrow indicates the direction of motion.
Change of wavelength caused by motion of the source. When an object moves toward you the wavelengths get shorter and the frequency higher. When an object moves away from you the wavelengths get longer and the frequency lower. Original: Tkarcher Vector:  Tatoute, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/&gt;, via Wikimedia Commons
An animation illustrating how the Doppler effect causes a car engine or siren to sound higher in pitch when it is approaching than when it is receding. The red circles represent sound waves.
The Doppler effect causes a car engine or siren to sound higher in pitch when it is approaching than when it is receding. The red circles represent sound waves. Charly Whisky 18:20, 27 January 2007, CC BY-SA 3.0 <http://creativecommons.org/licenses/by-sa/3.0/&gt;, via Wikimedia Commons

Below is a three minute video explaining the doppler effect and redshift.

I can add that the constancy of the speed of light in vacuum changes the exact size of the doppler effect. The doppler effect remains as is for the most part but the formulas for the classical doppler effect, which you would use for sound, and the relativistic doppler effect, which you would use for light in space, are different. It is just to pick the right formula.

Doppler Effect Formula on a green chalkboard. Education. Science. Formula. Vector illustration. | The Universe has a Redshift and its Increasing
The classical formula for the doppler effect. There is a medium (air) but you don’t need to consider the constancy of the speed of light in vacuum. You use it for sound and water waves. Shutterstock Asset id: 2365938267 by Sasha701.
Relativistic Doppler Effect Formula on a black chalkboard. Education. Science. Formula. Vector illustration.
The relativistic formula for the doppler effect considers the constancy of the speed of light in vacuum but there is no medium to worry about. You use this formula for the doppler effect of light in space. Shutterstock Asset id: 2416786951 by Sasha701.

Measuring redshift

A common misconception is that astronomers take pictures of distant galaxies and somehow measure the “redness” of them, but that is not the case. When you take a spectrum of a heated element (such as hydrogen or helium in stars) it creates characteristic dark lines in the spectrum — like a fingerprint. Everything on the periodic table has its own characteristic fingerprint of lines at characteristic frequencies. In addition to measuring the cosmological redshift it makes it possible to identify the elements in a star and their proportions. See the picture below.

The top shows a colorful spectrum from blue to red with absorption lines in black. The bottom portion of the picture shows the same thing expect the black absorption lines have moved a bit to the right.
Visualization of redshifted absorption lines are redshifted due to velocity away from observer. Top lines are for an object at rest and in the bottom picture the object is moving away. Maxmath12, CC0, via Wikimedia Commons. This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication.

Expanding Universe Hazy IPA

Expanding Universe is a Hazy IPA, or a so called New England style IPA from First State Brewing, ABV 6.5%, IBU 25 (IBU = International Bitter Units). The fact that it is an IPA (India Pale Ale) means that it is Ale and therefore not a Lager. The fact that it is an IPA means that it is hop-forward and has an intense flavor and aroma. The fact that it is a Hazy / New England style IPA means that it is more fruity than bitter and looks cloudy, hazy, like juice. The flavor of Expanding Universe is mango, pineapple, and grapefruit. It has a low bitterness, it is fruity, juicy, and it is great if you like New England IPAs.

The picture shows a glass with yellow to light orange hazy liquid. There are green plants in the background.
Expanding Universe ABV 6.5%, IBU 25.

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Author: thomasstigwikman

My name is Thomas Wikman. I am a software/robotics engineer with a background in physics. I am currently retired. I took early retirement. I am a dog lover, and especially a Leonberger lover, a home brewer, craft beer enthusiast, I’m learning French, and I am an avid reader. I live in Dallas, Texas, but I am originally from Sweden. I am married to Claudia, and we have three children. I have two blogs. The first feature the crazy adventures of our Leonberger Le Bronco von der Löwenhöhle as well as information on Leonbergers. The second blog, superfactful, feature information and facts I think are very interesting. With this blog I would like to create a list of facts that are accepted as true among the experts of the field and yet disputed amongst the public or highly surprising. These facts are special and in lieu of a better word I call them super-facts.

45 thoughts on “The Universe has a Redshift and its Increasing”

    1. No you are right Jacqui. Most people have heard of the expansion of the Universe. However, that it is red shifted as a result might be surprising and that the expansion is accelerating and therefore the redshift increasing might be surprising too. In fact if the dark energy explanation is correct and dark energy keeps increasing then it would keep expanding faster and faster and eventually ripping the Universe apart.

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  4. WOW Thomas…. your wealth of knowledge is unimaginable my friend. The pieces are slowly being put together.. Will we ever know the bigger picture of the Universe? I doubt it.
    But like the universe…. We are expanding our consciousness 🙂 xx
    Another mega fact finding post my friend x

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  5. This is fascinating! I’m sitting here listening to my carpet cleaners work, and it’s making me think of the Doppler effect you mentioned. The sound of their equipment definitely changes as they move around the room. It’s neat to connect that everyday experience to something as huge as the universe expanding. Thanks for making such a complex topic so easy to understand

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  7. Lulu: “Our Dada says he remembers watching Cosmos or something back in the day where Carl Sagan or whoever said they didn’t yet know if the universe would collapse back on itself and make another Big Bang or if it would expand forever until everything eventually ran out of energy and winked out. Our Dada was rooting for another Big Bang, but oh well. Not like he will be around to see it either way.”Charlee: “What?!”

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    1. Yes Lulu I remember that too. That the Universe is expanding faster seems to contradict that the universe would collapse back on itself. However, I read today that recent observations seem to show that dark energy is weakening and if that is true the expansion of the Universe could halt and reverse itself so the universe would collapse back on itself afterall. Charlee and Lulu I hope your Dada will be around to find out. According to a book I’ve read there is a restaurant at the end of the Universe.

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          1. If they allow dogs, I’m up for it! We’ll sneak the cats in too. Seriously though I would be happier to know that the universe will eventually collapse in on itself and start over than burn out. (I will mention that there’s a relatively recent book trilogy where this becomes a late plot point, but won’t name the series, because spoilers.)

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  10. Thanks for the good post. You’ve touched on a big part of what I do in my “day” job with the DESI survey at Kitt Peak National Observatory. I also was one of the observers that took data that led to the initial discovery of the accelerating universe.

    I think a common misconception is that we take pictures of distant galaxies and somehow measure the “redness” of them. That’s not actually what we do. When you take a spectrum of a heated element (such as hydrogen or helium in stars) it creates characteristic dark lines in the spectrum — like a fingerprint. Everything on the periodic table has it’s own characteristic fingerprint of lines at characteristic frequencies. The further away something is, the more those exact pattern of lines “shift” redward in the spectrum. So, if you measure one of the sun’s principal helium lines at a wavelength of 587.5nm, you’ll find that same line at a higher value (or in the red direction) for a redshifted galaxy. The difference in that value gives you the redshift of the galaxy according to the equations you gave.

    With the DESI survey we typically obtain tens of thousands of galactic spectra per night with the objective of creating the largest redshift map to date. Many of the most exciting discoveries about the expansion history of the universe are coming out of the DESI survey. Here’s one recent press release from just under a year ago: https://noirlab.edu/public/news/noirlab2512/

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    1. “I also was one of the observers that took data that led to the initial discovery of the accelerating universe.” – wow that is very exciting. Congratulations ! Regarding the common misconception that you astronomers somehow measure the “redness” of them made me realize that I should probably add a paragraph about that. I knew about this, I just didn’t say anything about it. So I added a brief section “Measuring redshift” (and a picture) towards the end. Also, thank you so much David for commenting and adding this very useful and enlightening information. It is a special treat everytime you comment and add to one of my astronomy related posts.

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      1. Thank you, Thomas. Yes, I suspected you did know. Interestingly, I know science writers who don’t like discussing spectra because they think their hard for the general public to understand. However, I think it’s just a matter of breaking down the information into familiar pieces. The principals really aren’t that difficult, it’s just something that requires a few steps to understand.

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  13. Fascinating stuff! The video was interesting and helpful. For some reason, I’ve never been a fan of the color red, even since childhood. (Deep greens and blues are the colors I choose… as James Taylor sang.)

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        1. You are right, so many people are colorblind. I recently read that dogs are not colorblind but the colors they see is shifted compared to us. They have a hard time with red, brown and orange, but they see blue and violet well and they can see ultraviolet, which we cannot see.

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