The Andromeda Paradox - When is "Now"?

recalibrate okay synchronization in three two one synchronization completely when is now arya and i now both agree on when now is but what about you and me as i'm filming this episode my present is technically your past and your present moment is technically in my future if i was there next to you right now we'd of course both agree on what now is don't don't touch me and it would be after some excruciatingly painful small talk i'm bringing up these differences because my question for you today is does the universe at large have a now okay nothing or is the present moment just a matter of perception now okay let's recalibrate again jesus now entering the facility in 1989 the legendary physicist robert penrose presented a paradox to the public he said consider two nerds very interested in the goings ons in the galaxy nearest our own andromeda and one day these two nerds are walking past each other on the street and they say hello nerd friend i would like to query you as to what is happening right now in the present of andromeda if they had amazing telescopes and didn't have to wait 2.5 million years for the light information to get to them the moving nerd looks at andromeda and says hark stationary brethren i see aliens and their elder councils debating whether or not to invade earth right now who voice but the stationary nerd looks at andromeda and says nary you fool they have already deliberated and their alien fleet is on the way right now to shoot laser beams at our faces the paradox here is that it is theoretically possible for these two nerds to disagree for one nerd to apparently see into the future of the other but how can two simultaneous observations of the present be different well to explain that i need to get changed arya activate carl sagan mode how should we define now how do we suss out what is truly simultaneous well to figure that out from scratch we must first consider the universe not just at one time but at all times i didn't have a turtleneck shut up suppose that we have a camera a camera of the imagination as carl might have and this camera allows us to magically take a snapshot of the entire universe inside of this snapshot in all of three-dimensional space everything should be simultaneous for example me talking to you a student on the other side of the world doing their homework and blurpon from the artemis cluster who's a good friend of mine hashing grebos all day like he usually does they are delicious now if we were to keep taking snapshots eventually would have this abstracted view of all of space and time that we could look at and piece together now many science communicators call this the universal loaf of space-time but that sounds weird and stupid it makes you think of bread i'm hungry you shouldn't be eating as many carbs as you are shut up i'm going to call this totally time every moment that the universe has had is having or will have in this higher dimensional view of t'tala time all time and all events really do exist there's a snapshot where everything is simultaneous for you your present but the past here isn't just a memory and the future isn't uncertain it's all there every single point in time equally as valid as your present it all happens now you might be thinking then if this eternalist view of the universe is true why do all slices as we define them have to look like this why doesn't a snapshot of the universe look like this or even this well that's a good question deactivate carl sagan mode different nows is the very heart of the andromeda paradox a paradox that may be impervious to common sense but not to einstein's theory of relativity oh come on what is what is going on with you today fun fact the andromeda galaxy is on a collision course with the milky way it's a fun fact because that's more than four billion years out and you are definitely not going to make it but whether we're here or not the milky way and andromeda are going to crash together however when this happens it's not going to be the cosmic calamity that you may expect you see space is big it's vast it's bigger than fast we don't have words to describe just how big space is and how large the distance between individual stars are so when you have andromeda with literally trillions of stars moving at 100 kilometers per second towards the milky way when they finally interact there's unlikely to be a single solar collision not one if we were still around in the solar system we probably wouldn't even notice this event happening as a wise man once said whoa now as we explained in our episode about the spaceships paradox how you move through space relativistically speaking can affect how you move through time more specifically if you move really fast through space approach the speed of light you move less in time this fact brings us back to our view of total time and now we should track our two andromeda interested nerds again in total time we will consider moving from left to right as moving from the past to the future so we have our stationary nerd and our moving nerd let's watch what happens as time evolves time presses onward and for our stationary nerd now should look like our slices from before this is their plane of simultaneity where everything in this slice can be considered to be happening at the same time for our moving nerd however who is moving through space and therefore moving through less time their plane can't be moving in the same way can it it must be angled without getting into too much college level physics here the plane of simultaneity must be angled for moving observers because of the nature of the speed of light from both theory and experiment we know that the speed of light remains the same no matter the reference frame for this to be true for moving observers who could look at something and disagree on the speed of it time and space must then shift to accommodate this universal speed limit and how much time and space shifts depends on just how quickly you're going how close you're getting to the speed of light if we go back to our paradox then we can observe that the plane of simultaneity for the moving nerd actually includes a present view of andromeda that is in the past of the stationary nerd two apparently simultaneous observations except one sees aliens and the other sees an alien invasion mbd and we can even calculate the size of this shifting effect but to show you how i must escape to the one place that hasn't been corrupted by capitalism space i'm tim curry from command and conquer andromeda is what astronomers call very far away 2.5 million light years away in fact and so in our view of totality andromeda will also be very far away from our nerds now when you walk past someone on the street your space-time shifting will hardly be anything because when you're walking you're not even close to the speed of light but if your plane angle of simultaneity changes just fractions of a degree it can really add up somewhere really far away like andromeda which is 24 million quadrillion meters away so if we use an equation oh like this one which takes into account time dilation we plug in how far andromeda is away from earth we can see that if you're just walking past someone else at one foot per second which is hardly even a stroll your view of the present in andromeda could differ by as much as a full earth day and if one nerd was going as fast as i am in this awesome spaceship admit it their view of the present moment in a galaxy far away could differ by literally years and kyle i hear you asking in this tone of voice why is there an equation floating in outer space who cares arya take us in the differences between the nows of different observers is called the relativity of simultaneity and it solves the andromeda paradox because of the immutable speed of light two relatively moving observers will never actually agree on what the present moment is they can't this isn't a paradox it's two equally valid assessments of the present moment from different perspectives and because of this it doesn't really make any physical sense in the first place to talk about the now of you and something very far away because of the speed of light and how information travels so when is now well that depends on who you ask until next time now exiting the facility thank you so much to the very nerdy staff at the facility for their direct and substantial support in the creation of this video today i especially want to recognize research assistant solomon de berry and visiting scholar jack akers private eye if you want to join the facility if you want to get on the staff and join the nearly 1200 nerds who every day are coming up with episode ideas for me talking to me in the discord having their own game nights dnd games trivia nights and commander league and radio stations and all the other perks you can go to patreon.com kyle hill right now and get on the staff and if you support the facility just enough you get your name on aria here each and every week and as you can see there's literally hundreds of you so i don't know how i'm gonna pass the look i'm not gonna sugarcoat it this stuff is hard to understand and when i was re-wrapping my mind up around all this uh relativity stuff some videos by my colleague minute physics were very very helpful who did an entire course on relativity and simultaneity and all that stuff so i'd recommend those videos oh still so much more i hope nothing weird happens when i leave just your friendly neighborhood ti-89 here remember to shut off your calculator when you're not using it to save battery even though the batteries decrease by just about one percent a month i still would might appreciate it thank you and thanks for watching i'm so i'm so glad nothing weird happened thanks for watching

Channel: Kyle Hill

Views: 632,315

Rating: 4.9250321 out of 5

Keywords: because science, engineering, kyle hill, learning, math, physics, science, stem, the facility, twin paradox, special relativity, time dilation, paradox, andromeda, galaxy, space time, paradoxes of relativity, roger penrose, kyle hill channel

Id: e0C21L38mCA

Length: 11min 9sec (669 seconds)

Published: Fri Aug 07 2020