thanks to brilliant for helping support this episode hey crazies there's this super uniform microwave static coming from all directions seriously all directions it's the cosmic microwave background the CMB tune your radio telescope to the right frequency range and you get static no matter which way you point it here static there static everywhere static which you know is kind of weird but what is it where did it come from and frankly why should we care this episode was made possible by generous supporters on patreon so we noticed pretty quickly that the static wasn't all the same frequency as you turn the frequency knob the signal gradually gets louder hits a peak and then gets quieter again we can even figure out the intensity of each of those frequencies and plot it on a graph when we do that we get something that looks like this it's a thermal spectrum what's a thermal spectrum it's light emitted because of temperature so you've got a rock sitting on a table the reason you can see it is because light is reflecting off of it but let's say you painted it with the blackest paint you could find now we'd call it a black body which is just an object that's black when cold it might not be able to reflect light anymore but it would still be emitting light in infrared just because it's at room temperature that light is made by the molecules inside the rock if we make the rock really hot though we can get it to emit visible light the thermal spectrum which is peak in a different place we could even figure out the temperature based on where the peak is as it turns out the CMB is also a thermal spectrum it just Peaks in the microwave range instead of the visible range based on where it Peaks we know whatever is emitting this light is about 2.7 Kelvin and let me tell you this spectrum is as close to perfection as you can get just to give you an idea of how perfect this is the sun's thermal spectrum compared to the ideal curve based on its temperature it might be close enough to call the Sun a blackbody but it's not perfect doing the same comparison for the CMB gives us this look how beautifully it matches hmm good stuff it's as close to a perfect thermal spectrum as you're gonna get which leads to an obvious question what the heck is emitting this thing could space itself be emitting it I mean space is pretty black seriously check this out I can color this paper with a sharpie and it seems pretty black right now look what happens when I poke a hole in it and put a dark void behind it see how much blacker that dark void is space is the blackest black but hold up if this black void started emitting light we have to assume there was some kind of matter inside it after all the temperature is atomic jiggles and you can't have atomic jiggles without atoms hmm let's see for something that cold it's a pretty strong signal like seriously 2.7 Kelvin just a few degrees above absolute zero that's cold plus it's coming from every direction what could possibly be everywhere wait a minute microwaves are just the type of light and the speed of light is finite if this thing's coming from far enough away it could be coming from the distant past to the timeline no no not when it was discovered when it was made if you want to learn about the discovery of the CMB you can check out physics girls video it's a good one you might even recognize a name or two in the end credits but no I mean the cosmic timeline we're talking billions of years ago before there were humans before the earth formed before the first stars in the galaxy lit up before there were even atoms in the universe space was filled with plasma that's not the stuff in my blood right no you you definitely don't want this kind of plasma in your blood plasma is a soup of charged particles it's way too hot for neutral to exist but say you and one of my clones are floating around in it with invincibility powers you'd both see a pale orange light coming from every direction not from everywhere in the universe though during the plasma years the universe was about 80 million light years across but you could only see a few thousand light years in any direction that's only one ten thousandth of the way across the universe see light doesn't get very far in a plasma it keeps bumping into charges like protons and electrons it was like a very violent pinball game the light was constantly being created and destroyed that light was far more likely to be coming from nearby if my clone were to drift away from you he gradually be obscured by a fog of particles that all changes when neutral atoms happen the universe was continuously expanding and cooling off when it got to an age of about 380,000 years old it dropped below a temperature of 3000 Kelvin that plasma that was filling the universe stopped being a plasma electrons and protons came together to form neutral hydrogen with the charges gone light was free to move through the universe unobstructed the universe became transparent we called that period in cosmic history recombination because names are dumb sometimes the light emitted during that time is the same light we're receiving as the CMB that static we get from all directions was created during recombination when the universe was only about 380,000 years old at the time the temperature was 3000 Kelvin so the distribution peaked in the near infrared there was quite a bit of visible light in there hence all the orange you'd see if you were around back then but a long time has passed the universe is much bigger and much cooler now it peaks in the microwave range that corresponds to a temperature of 2.7 Kelvin it's still a thermal spectrum just a much colder one but remember how I said the spectrum was as close to perfect as you can get well close to perfect not the same as perfect there are some tiny temperature variations the CMB has spots the blue spots are slightly colder and the orange spots are slightly hotter of course this is the universe so those spots are enormous today there are about 550 million light years across like I said enormous but when those spots were made the universe was 1,100 times smaller they were only about half a million light years across at the moment of recombination and those spots were made with sound waves the density of that primordial plasma wasn't perfectly uniform the slightly more dense parts collapsed under gravity and then rebounded in a shock wave that travelled over half the speed of light that's how we know how big they are before recombination when everything was a plasma matter and light were coupled remember the pinball game light didn't get very far without interacting with matter so any changes in the structure of matter were accompanied by the same changes in the pattern of light but during recombination everything changed light became decoupled from matter and the pattern of light was frozen that pattern is what we see in the Cosmic Microwave Background this is a map of the structure of the universe when it was only 380,000 years old and that map tells us a ton about the universe like a crap time stuff that lets us model the entire timeline of cosmic history of course the CMB is not the only place we get that information it's important to collect corroborating data from multiple sources like patterns in the location of galaxies this structure matches the CMB that simulation was created by a supercomputer called Mira I got to see it in person a couple years ago it was a great experience there's a blog if you're interested anyway modeling is important because we can only see as far back as the CMB it's the oldest light in the universe any physical record of the universe before that was destroyed almost immediately all we have for that era are the models and data we collect from particle accelerators so what's the CMB it's the Cosmic Microwave Background it's cosmic because it fills the observable universe probably the entire universe to its microwave because it peaks in the microwave range of the electromagnetic spectrum and it's a background because it's a very uniform signal coming from all directions the CMB is a thermal spectrum leftover from when the universe was only 380,000 years old the CMB is an afterglow from the Big Bang it's a record of the distant past so got any questions about the Cosmic Microwave Background please ask in the comments thanks for liking and sharing this video don't forget to subscribe if you'd like to keep up with us and until next time remember it's okay to be a little crazy if you want to learn more about cosmology brilliant is a good place to start their astronomy course begins by teaching you the tools scientists use to study the universe it ultimately ends with several cosmology quizzes one of which is on the cosmic microwave background astronomy is just one of over 60 interactive courses and math science and computer science that brilliant has to offer try adding some learning structure to your day by setting a goal to improve yourself and then work at that goal just a little bit every day brilliant makes that possible with interactive explorations and a mobile app that you can take with you wherever you go if this sounds like a service you'd like to use go to brilliant org slash science asylum today the first 200 subscribers will get 20% off an annual subscription [Music] if gravity is a gradient in time how can gravity affect photons they don't perceive time right right photons don't personally experience time but they're not taking the measurements we are in an our reference frame they are traveling through space and time anyway thanks for watching
