We can see things moving faster than light

imagine a galaxy and its light took 25 000 years to get to us how far away is that galaxy uh 25 000 light years away beautiful now imagine a galaxy that it took the light 13.4 billion years for the light to get to us how far away do you think that galaxy is i would imagine it's 13.4 billion light years away the answer is actually 32 billion light years how does that work wait yes i got the first one right there's a galaxy that we actually discovered in 2016. it's called gnz11 it took about 13.4 billion years for that light to get to us but the galaxy right now is 32 billion light years away how is that possible i don't know brain's already broken the universe was just like this stagnant thing you know like all these rocks are where they are and light is emitted from that rock all the way over to this rock if nothing moved and it took 13.4 billion years for the light to get across from one to the other then they would be 13.4 billion layers apart but imagine the space between all the rocks and dirt imagine that's all expanding with the rocks so as lights traveling across the distance between the rocks is getting bigger and bigger so even though it only took 13.4 billion years for the light to get from gmz11 to us we are now 32 billion light years away from that galaxy the universe expanded in that time yeah i think this is one of the most unintuitive things about the universe space itself can expand when i first learned that the universe is 13.8 billion years old so the edge of it should be 13.8 billion light years away so they always talk about distance when they talk about light years but it's not it's 46 and a half billion light years away i have to call myself out here because when i talk about the size of the universe what i meant was the size of the observable universe which is the sphere of stuff that we have been able to see so far because light has had enough time to get to us our observable universe is growing we don't know how big the universe is we don't even know if it has size anyway the observable universe is a lot bigger than i thought i was so confused how is it possible for the universe to be so much bigger than light has had time to get to us that concept to me is so confusing and mind-bending but it comes because all of space is expanding and stretching in the entire universe space is not this stagnant thing it's not like this field of rocks all of the space-time is spreading apart there's more and more space being created and the effect of that is that space is expanding with galaxies and carrying them apart from each other you start to notice that galaxies are actually receding away from us so the further away they are the faster they're moving away from us something that's a mega parsec away from us is moving at 70 kilometers per second away something that's twice that so two megaparsecs is moving at 140 kilometers you can keep going eventually until you get to 299 000 kilometers per second do you know what that speed is is that the speed of light yes yeah it's the speed of light so eventually you get to that speed and you plug it into your equation and you get that the distance away from us to a galaxy that's moving away from us at the speed of light is about 14 billion light years away and that is far within the boundary of the edge of our universe here's us we're you know where we are at the center of our observable universe and then if you go in all directions out 14 billion light years you get a sphere and that sphere is called the hubble sphere beyond which everything is moving away from us faster than the speed of light and it's not a little bit of stuff it is 97 of all galaxies in the universe are moving away from us faster than the speed of light it's not just a couple it's crazy just trying to process it honestly here's a question do you think that we can see things that are moving away from us faster than the speed of light well now that you said it it doesn't sound like we could or will ever be able to right [Music] before we learn how things can move faster than the speed of light i want to share the sponsor of this video 3m and also my masterpiece turn the lights off and we're going to turn the flash on and take a picture again it's so bright ah this is made with 3ms retro reflective tape how they work totally surprised me if you look closely at the material there's these microscopic beads with perfect reflection angles so that more light reflects directly back the direction it came 3m is a pioneer in developing the science behind retroreflection and has been advancing the technology in new and groundbreaking ways for 80 years their products keep you safer by making you more visible in any kind of weather or condition situation like running at night which i like to do and it looks kind of rainbowy sometimes ah that's so cool that's because it's it's little glass beads like little raindrops you probably have a 3m product within arm's reach in your room wherever you are you know i think that science is amazing but the people who take it and are super creative and make technology that's where the butter is at as a company their mission is improving lives with science which is why they want to inspire the next generation of stem innovators so every october 3m's young scientist challenge allows students to meet their superheroes and work with 3m mentors to turn their ideas into reality the finalists of this challenge are being announced in a few days but they hold the challenge every october so maybe you know someone who can participate all right thank you so much to 3m for supporting physics girl and now back to me explaining to levi how things can move faster than the speed of light slide transition that was good yeah how is it possible that something is moving faster than the speed of light if the speed of light is the fastest thing in the universe the fastest thing like the the ultimate speed limit the universal speed limit what you're referencing is einstein's special theory of relativity which says that nothing can move through the universe through space faster than the speed of light and that's true but space itself can expand and the space between two objects can expand such that it moves those objects apart faster than the speed of light so nothing is actually violating special relativity nothing is moving through space faster than the speed of light here's a question do you think that we can see things that are moving away from us faster than the speed of light well now that you said it it doesn't sound like we could or will ever be able to right if if something moves faster than the speed of light we will never see it via light it's a good guess i mean that's like what you would intuitively think yes we'll never see that galaxy as it is we'll only see it for how it was when the light left it so what you're saying is like you can imagine getting light from a distant galaxy that the light was emitted like far in the past when things were a lot closer together and then now we're seeing that light but we will never see those galaxies as they are now okay you are right and wrong cool i'm glad i'm glad i came so okay that galaxy we talked about at the beginning gm z11 that galaxy is about 31.96 billion light years away from us now so that galaxy is moving away from us like three times the speed of light or something like that but you're right we're seeing it as it was 13.4 billion years ago now it might not even be there anymore like all the stars might have burned out it might have been swallowed by another galaxy it's crazy to think that there's a galaxy we're seeing that might not even be in existence anymore no that's crazy so you're right there are some galaxies that are spaces expanding them away from us fast enough that we will never see them as they are now but there are some galaxies that are outside of our hubble sphere so meaning that they're moving away from us faster than the speed of light but we will be able to see them as they are now so they're emitting light now and it will get to us this is crazy you look confused you should be you're correct it's okay the galaxy's moving away from us faster than the speed of light it emits light at us and initially that that light moves away from us but it's traveling through space until it gets inside of our hubble sphere and it's no longer moving away from us um let me draw it here's us and then here's like shells of distance away from us so imagine like this is the hubble sphere so this galaxy is moving away from us faster than the speed of light because of the expansion of the universe emits light toward us which initially you know because the light was emitted from this object going faster the speed of light it's going to be moving away from us so the light's moving away but it it's making its way slowly this way even though this part is moving away from us it's making its way slowly and then eventually it's going to get to distances that are think about it like this so remember how i talked about how consecutive distances or distances that are further and further away from us are moving faster and faster so this right here is say moving i don't know 10. this one's moving 20. so as the light goes this way now it's going into space that's moving less and less fast away from us because the expansion rate of the universe or the hubble parameter is slowing down which means that the stuff that's now at that first circle is not moving away from us as fast as the stuff that was there does that make sense the light does this crazy path where like almost like a boomerang it's like it goes forward ignore this light emitted here goes forward away from us and then comes back toward us and eventually gets to us does that make sense no it doesn't make sense but it's cr so as light gets closer to us it starts moving faster and faster relative to us there are galaxies that are outside of what we call the event horizon the cosmic event horizon isn't and outside of that all the galaxies and stars outside of that we'll never be able to contact them they'll never be able to send light to us and the hubble sphere the edge of it is the event horizon no those are actually two different things the hubble sphere is inside that everything's moving less than the speed of light event horizon is everything that we can see there's actually a boundary between those two it's like a shell between those two stuff that's moving away from us faster the speed of light but the light being emitted from those things now will eventually get to us that's what's inside that shell it's like this magical shell and our hubble sphere is also expanding more light is coming inside of our sphere of things that are moving away from away from us faster than the speed of light because the universe is expanding but since the universe is expanding then light can be emitted from a galaxy initially like this is so nuts but the light will move away from us to start and then eventually stop and then start coming toward us relative to us which seems like that's violating relativity but it's not because it's moving through space still at the speed of light because space is expanding do objects get bigger when the universe expands great question um objects do not get bigger no actually so things can be easily pushed and pulled through space it's almost like they had like space has no friction i can easily pull you toward me i won't because i like this camera like i'm overcoming i don't know space so easily gravity overcomes the expansion of space up until you get to something like a hundred million light years so the local clusters of galaxies are not really affected by the expansion of space i mean yeah things are in space and then space expands and moves and the things go with it but that's not true if there's something else there to overcome that movement [Music] you

Channel: Physics Girl

Views: 2,325,183

Keywords: physics girl, dianna cowern

Id: q67vH0SKahU

Length: 11min 53sec (713 seconds)

Published: Fri Oct 15 2021