Daniel and Jorge Explain the UniverseDaniel and Jorge explain how the speed of light limits how events play out in the Universe.
Learn more about your ad-choices at https://www.iheartpodcastnetwork.com
See omnystudio.com/listener for privacy information.
If you love iPhone, you'll love Apple Card. It's the credit card designed for iPhone. It gives you unlimited daily cash back that can earn four point four zero percent annual percentage yield. When you open a high Yield savings account through Applecard, apply for Applecard in the wallet app subject to credit approval. Savings is available to Apple Card owners subject to eligibility. Apple Card and Savings by Goldman Sachs Bank USA, Salt Lake City Branch, Member, FDIC terms and more at applecard dot com.
Have you boosted your business with Lenovo Pro yet? Become a Lenovo Pro member for free today and unlock access to Lenovo's exclusive business store for technology expert advisors and essential products and services designed just for you. Visit Lenovo dot com slash Lenovo Pro to sign up for free. That's Lenovo dot Com slash Lenovo Pro Lenovo unlock new AI experiences with Lenovo's think Pad x one carbon powered by Intel Core ultraprocessors.
When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact, but the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
Plug in a HUNDAIV and the extraordinary happens. From the charge time and range in the Ionic five and six to the adventurous spirit of the ConA electric to the six hundred and one horsepower Ionic five and hyundaievs make the extraordinary electrifying.
There's joy in every journey.
EPA estimated threehund of three mile driving range for twenty twenty four in five se sel limited real wheel drive and three out of sixty one mile driving range for twenty twenty four Ionic six S long range real wheel drive with fully charged battery. Actual range may vary. Its a hunt to USA dot com or call five six two three one four four six O three for more details.
Hey or Hey, do you ever wish that the speed of light was faster?
I guess I'm not dissatisfied with the speed of light. I'm just glad it's not slower, because you know, I don't want to wait ten minutes after I flip on a light switch.
But you know, if it was faster and then we could see like further out into the universe. M that's true, and then we might be able to travel further to explore the stars.
Also true. But there's another side to it, as always, Well.
How could it be bad to have a faster speed of light?
Well, if light speed was a million times faster than technically, any alien out there in the universe could kill us instantly with a death ray.
Well, that's true. But you know, witnessing an alien death ray would be pretty cool.
It would be pretty cool for about a nanosecond, and then you'd be dead. Also, I'm pretty sure a death ray would be hot and not cool.
Might still be worth it.
Just for that nanosecond, you would know that eighties.
Existed, as my brain is getting for.
Hi am Jorge Am, a cartoonist and the creator of PhD comics.
Hi, I'm Daniel. I'm a particle physicist, and I don't spend a lot of time worrying about alien deathrays.
You don't, do you know something I don't.
I know that the speed of light protects us from most of the universe shooting us with alien deathrays.
Really like it forms a force field around us, protecting this like a blanket helping us sleep at night.
It just makes it kind of ineffective. If you're going to shoot an alien death ray millions of light years, then you're going to kill your target in millions of years. And like, whose geopolitical strategy really has that long an arc to it?
But what there are patient aliens? Then we're toast.
Then we might literally be toasted.
Welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.
In which we beam our joke rays into your brain, hoping to transmits some of the incredible wonder and knowledge about the universe, all the things that science has learned about this Bonker's wondrous, beautiful, glittering cosmos, and all the things that science is still working on, all the big questions about how the universe got here, where it's going and who lives in it?
Yeah, and how to actually build a joke ray. I mean that's probably the next Noble prize. The question is, doesn't make you grown or does it make you laugh?
Is that where you're going to ask when the aliens come, I'm gonna be like, tell us the secrets of space time And you're like, have you developed the joke Ray yet?
Well? Think about what it would mean for the mental health of humanity. You know, we could just have a laugh about everything.
Laughter is the best medicine. So anytime you go to the doctor, they're just like, yep, we're prescribing you five shots with the Joke Ray.
And then as the aliens as they you know, enslave us and possibly eat us, we could be laughing all the way. But it is a bizarre and jokey universe because it seems like a lot of it is beyond our control or even beyond our ability to ever interact with it.
That's true, and it's also sometimes beyond our ability to really understand. We have one way of thinking about the world where things move and slide and the way time works, But about one hundred years ago we discovered that that wasn't really the way it works, that there were different rules that things change when you move fast or when space is bent, and that we needed new rules and new ideas to understand what actually goes on in this universe.
Yeah, because I guess we realized a few hundred years ago that the universe, the world doesn't really behave the way it behaves like on an everyday basis, like when you're juggling baseball or you know, bouncing at basketball, Like that's one way that we think of the world as working. But really, like if you get down to it, in some situations, it's totally different.
Yeah.
In fact, there are really fundamentally different rules that govern how things move and how time flows. It just happens to be that in certain situations, like when you're moving really slow and when you're far from a black hole, things look a lot simpler. So we're living in so of a simplified corner of a very weird, very complicated universe.
Right, It's almost like we're in a special case, like our perception of the universe. It's like a small example of all the ways that the universe could be.
It's like you're playing the warm up levels on some video game before all the bad guys come in, just you can sort of like figure out how the controls work. Right, That's what we've been doing for physics for like thousands of years and now we finally understand the full scope of the game.
And wouldn't be great if a good respond in this universe? We can just keep trying.
Well, we sort of do. I mean, like physicists start from where previous generations of physicists ended, right, we don't have to start from scratch on physics every single generation, So physics sort of respawns in our minds.
Right, We're going to run out of lives at some point? Do we need to put in more quarters into the arcade of the universe?
That depends on the alien death right.
Or the joke ray Either one might help us or not help us. But yeah, the universe is kind of tricky, And it's tricky not just in like extreme situations like in a black hole or moving a close to the speed of light, because who knows, like we could be moving right now really fast compared to other aliens and other galaxies.
Right we are. We are moving really fast compared to the Sun, and the Sun is moving really fast compared to the center of the galaxy. But all those things are kind of abstract. What really matters is your speed relative to the people who are watching you, and relative to your clock. And so that's something that special relativity has taught us, is that the world looks different from different perspectives. Based on who's doing the measuring. You can get kind of a different account of what's going on and what's happened in the world.
Yeah, you might not agree with your relatives about relativity, but yeah, things are kind of tricky in this universe, and so even physicists sort of struggle with it, right, I mean, it's sort of hard to wrap anyone's head around these topics and how it actually works. And so physicists have some ways to kind of think about how these things work that might help other people.
Yeah, because in science we have our intuition, like give a feeling about how they might work and what might happen and how things are put together. And then there's the mathematics. And the mathematics is what actually happens, what really is going on, the rules that really do control the universe. But sometimes you look in at like a page of equations and you're like, hm, I don't see it. I don't really get it. And for me personally, it's easier to think about these things like geometrically to understand like the relationship in space and time of these things. So sometimes you can get more of an intuition for weird things if you think about their structure and space and time sort of geometrically, like the shapes that are created by all these ideas, Right.
And then you draw cartoons about it, which is where I come in, right exactly. It helps to draw cartoons.
No joke. Cartoons are a great way to visualize this. So that's why you and I work together on a lot of these books, and folks out there should check out our book We Have No Idea, which has all sorts of really clever cartoons visualizing really tricky concepts.
Yeah, and our upcoming book which is coming out in a few months frequently ask questions about the universe, which you can pre order right now. Man, we totally snuck in those book plugs, Daniel, totally unplanned.
I keep getting emails from listeners saying, you guys should write a book. I'm like, what would we not talk about the book enough on the podcast?
I guess we don't. We should talk about it every time.
I think we should, honestly. Anyway, back to the podcast, Yeah.
Back to the podcast. Let's talk about one of these tools that physicists used to kind of wrap your head around some of these triggery concepts about relativity and the speed of light. So today on the podcast, we'll be asking the question what is a light cone? Now, Daniel, this is a light cone? I think, I guess you mean light, not like not heavy cone.
Yes, exactly, light as in photons is in that thing that speeds along at the maximum speed of the universe.
Now, this sounds sort of like maybe a dessert, but maybe we're not desert you want to eat or that would taste very good.
Sounds like the kind of desert your mom would order for you when what you really want is a scoop of ice cream.
He really want is a heavy cone, the heavy cream cone. You don't want the like fat free light cone. But yeah, So this is a concept that comes up in special relativity and it has some pretty interesting consequences about causality and like what's actually real or like what's actually happening or happened in the universe.
Yeah, and it helps you think about what's going on inside a black hole and even possibly maybe allows you to figure out a way to do real life time travel.
Sounds like a very powerful dessert here. All right, Well, before we go on, we just want to give a quick shout out to Bjorn, right he sort of helped inspire this episode. Daniel.
Yeah, thanks Biorn from Sweden who sent me a link to his Solar System inspired music which I listened to while preparing for this podcast. You can find him on Spotify at ort cloud Services. Check them out if you like sort of space ambiance music. Thanks a lot, Biorn for sharing your music.
Yeah, and again that's or Clouds. That's OORT cloud Services on spotif which is a pun because it's like the Orc Cloud and also cloud services.
And what has the orc cloud done for us recently? Well, I guess it delivers spacey music.
And you can upload your pictures to it.
You might never get them back, but yeah, you can upload them.
Well, it probably takes like twenty years just to get there, and then the download speed is probably even worse. All right, Well, we were curious, as usually, how many people out there are familiar with the const we're talking about today, So Daniel went out there into the internet to ask people what is a light cone.
And if you are out there on the internet and always wanted to participate in a podcast, Please write to us two questions at Danielanjorge dot com and you can be unprepared to answer future questions for the podcast.
Right, and if you're not on the internet, please tell us your secret. I mean, I would love to sometimes not be on the internet. I guess we're on the radio too, right, Daniel. I think some stations broadcast is so they might be listening on the radio.
Yeah. So thanks everybody who's out there listening to us on the radio as well. We appreciate all of your support and all of your listening. Did you know that we recently passed fifteen million episode downloads?
Wow? Really, really, it's amazing. That's like fifteen million hours that people have been listening to us.
That's like fifteen million banana jokes at least.
At least because you know, we're a multi banana joke death Ray A joke Ray here.
We try to in our in our best episodes.
Like a shotgun rate joke. Ray. Really, we just splatter banana peels all over the place.
Now, I'm imagining fifteen million tiny bananas coming out of the nozzle of a gun at very.
High speed, coming out of our mouth. That's a little disturbing. But anyways, think about it for a second. If someone asks you what you think a light cone is, what would you say. Here's what people have to say. I would say, that's what comes out of the shiny end of a fleshlight.
I believe this is a space time diagram where it shows a three dimensional object and as you go up, that's time passing, so it makes a cone. Like if you look at the diagram of the Big Bang and we show a tiny point, then it slowly goes up into a cone as time progresses.
I don't know what a light cone is I'm thinking about. There was some propulsion idea that was I think it was largely theoretical, but it was to do with kind of using light to push spacecraft and it would capture the light using light sales. I don't know if that would be to do with it. I remember seeing a model in the Science Museum in London, but it was a cone, but that was probably just because it was made of plastic.
A light con is a representation of how from the light travels from a point. For instance, if you have if I have a flashlight in my hand, then I try it on the light bulbs travel in space and time like a cone.
You can represent that as a cone.
That is something I've heard of before. It's the realm of like what you can see. So it's like ninety three billion light years across is in our observable universe, because that's like how far we could observe or something into space, or like the photons that have reached us from that distance. Although I don't understand how that's bigger than thirteen point eight billion light years since that's the age of the universe. But I'm still quite unclear on that. But I know that the light cone is basically all that we can see within our realm of light, anything that can reach us in any form.
I think a light cone is an ice cream cone that's been left out in the sun too long and all the ice cream melted.
A light cone is an ice cream cone that has no chocolate ice cream in it whatsoever, which is fundamentally flawed, and I think it violates one of the laws of thermodynamics, because why would you want vanilla ice cream when chocolate is an option? So light cones make no.
Sense, all right. A lot of people went with my interpretation, which is that it sounds like a dessert possibly, and that it's light.
Yeah, and we also heard some people throwing shade on vanilla ice cream. Wow, that was rough.
I know, how can you be down on vanilla ice cream? It's like the nicest flavor gets along with everybody.
That's true. I mean I would always pick chocolate over vanilla. But you know, if all you got is vanilla, I'm happy to eat it.
But if you take vanilla and sprinkle chocolate on it, See that's the versatility of vanilla.
Or take chocolate and sprinkle chocolate on it, still better.
But you can't take chocolate and sprinkle vanilla on it.
That's literally when I do that, the vanilla doesn't add to anything. It's just sort of like the substrate.
A lot of mean, it makes most cookies taste good.
It's just sort of vanilla. That's the reason why they call it vanilla vanilla, you know.
Because it's so dependable and and solid and just always there for you.
Right.
Yeah, if somebody reads your writing and they describe it as a vanilla, when you take that as a compliment.
Depends am I writing the back of an ice cream carton? Then it would meet its goal. But yeah, so a light cone, Daniel tell me, this is something I was surprised to see in our topic because it is it's a graphical interpretation of physics, right, And so it's a little tricky to describe on a podcast.
It's a little tricky to describe on a podcast. We'll see how we do. But I thought it was useful because I find that every time we talk about special relativity, I have light cones in my mind. I got these things in my brain. They really helped me think about sort of the structure of space and time, and they lead to a lot of interesting consequences. And so I hope if we can somehow download the concept of a light cone into the minds of our listeners, it'll help them think about special relativity.
We need like a light cone ray to shoot this into people. Maybe.
Yeah, I think it's a podcast starring me and you talking about physics.
Yea throwing out Banema Jones. All right, well we'll step us through it. What is technically a light cone?
So a light cone defines the part of the universe that you can influence, the part of the future that you can visit geometrically, you can think about it like if you turn on a flashlight for a moment, so you shine photons in every direction, they leave you in sort of a sphere. After one second, they are one light second away from you. After one year, they are one light year away from you. So imagine a sphere, and then that sphere is sort of growing as time goes on, right, So that set of spheres versus time as those spheres grow, this is your future light cone. This is the part of the universe that you can influence, where your choices, the things that you do as a person could have sort of an effect downstream. It's very easy to understand why. The reason is that everything that's outside of that growing set of speares you can't influence because information would have to travel faster than the speed of light to get there. So it's a re direct outcome of the fact that we have a maximum speed limit to the universe. It divides the universe into parts you can influence and parts you cannot. So the light cone is the part of the universe including the future. Right we're talking space and time here, the part of the future universe that you can have any sort of influence over.
So I turn on a light like a light bulb, and that light is growing comes out of the light bulb, grows in a sphere, and you're saying, that's the light cone. So really should be called like a light sphere. Maybe, yeah, that'd be a better name. Like the light sphere is the sphere around you which you can reach with light.
The reason it's often called the light cone is that it's hard to draw four dimensions on a sheet of paper. The most we can really draw on a sheet of paper is three dimensions, you know, by having like some perspective, and so you need to have time on there. So you can really only have two other dimensions of space on your sheet of paper. And so when you're drawing these diagrams, people typically treat space as if it was two D surface instead of like our three D world, just to sort of simplify it. So in two dimensions, the sphere we were just talking about becomes a circle.
Right.
Imagine, for example, taking a smooth sheet of water and hitting it somewhere. What happens You get a wave that leaves where you hit it, and it travels outwards. So now you get a set of circles. Now, if you take those set of circles and you extend them like vertically above the surface in time make time that vertical direction. Then what you get is a cone. Right. It starts from a point when you hit the surface of the water, and then as time goes on, that circle gets larger and larger, and that defines a cone. So it's a cone only in a sort of universe that has two spatial dimensions and one time dimension.
Right. It's kind of like if you take a slice of those light spheres we were talking about, Like if you take a slice of it and you see those that circle on that slice growing, and then you imagine that circle growing but growing and also moving up maybe at the same time, then it kind of makes like.
A yeah exactly, and it moves up. Because now we're imagining time to be one of our axes. Right, we have two dimensions of space and we have another direction, which is time. And obviously things just flow forward in time at one second per second, and so this circle just sort of grows in time. If you instead had something which wasn't moving, right, if you just like drew a circle around you, then that circle would slide through time and make a cylinder, right, because it wouldn't be growing. But if it is growing, then it makes a cone. It starts from the point where you've made it, and it makes a cone.
And I guess if you're having troll visual license, you can always just pop on Google images or something and look for light cone. I imagine you'll get a picture of this, right.
How do people do podcasts before Google image search?
Anyway, they probably avoided topics that involved geometry and multiple dimensions. But it's kind of an interesting concept, and I think you as a physicist, you like it because it defines kind of like a volume, right, It defines kind of like a set of space time that is either inside the cone or outside the cone. That's kind of the power of this kind of visualization.
Yeah, and it's not just arbitrary, like you can make whatever shape you want in space time. But this one is special. This one is really important because everything that's inside your future light cone are things that you can influence. Right. You can't send a message to anything outside your future light cone, Like anything outside your future light cone by definition is too far away for any message to reach because you would have to travel faster than the speed of light. And if you can send a message. It means you can't send any information. It means you can't influence it at all. And one of the really tricky, complicated things about special relativity is that it plays sometimes with like the order of events, and it seems to have consequences for causality. So this helps you sort of keep track of that the part of the universe that you can influence, and also looking backwards, the part of the universe that can influence you.
Right, all right, well, let's get into some of these weird consequences for causality and simultan and alien death rays. But first let's take a quick break.
With big wireless providers, what you see is never what you get. Somewhere between the store and your first month's bill, the price you thoughts you were paying magically skyrockets. With Mintmobile, You'll never have to worry about gotcha's ever again. When mint Mobile says fifteen dollars a month for a three month plan, they really mean it. I've used Mintmobile and the call quality is always so crisp and so clear I can recommend it to you, So say bye bye to your overpriced wireless plans, jaw dropping monthly bills and unexpected overages. You can use your own phone with any mint Mobile plan and bring your phone number along with your existing contacts. So dit your overpriced wireless with mint Mobiles deal and get three months a premium wireless service for fifteen bucks a month. To get this new customer offer and your new three month premium wireless plan for just fifteen bucks a month, go to mintmobile dot com slash universe. That's mintmobile dot com slash universe. Cut your wireless bill to fifteen bucks a month. At mintmobile dot com slash universe, forty five dollars upfront payment required equivalent to fifteen dollars per month new customers on first three month plan only. Speeds slower about forty gigabytes on unlimited plan. Additional taxi, s fees, and restrictions apply. Seementt mobile for details.
AI might be the most important new computer technology ever. It's storming every industry and literally billions of dollars are being invested, so buckle up. The problem is that AI needs a lot of speed and processing power, So how do you compete without cost spiraling out of control. It's time to upgrade to the next generation of the cloud Oracle cloud infrastructure or OCI. OCI is a single platform for your infrastructure, database, application development, and AI needs. OCI has fourty eight times the bandwidth of other clouds, offers one consistent price instead of variable regional pricing, and of course, nobody does data better than Oracle, So now you can train your AI models at twice the speed and less than half the cost of other clouds. If you want to do more and spend less, like Uber eight by eight and Data Bricks Mosaic, take your free test drive of OCI at Oracle dot com slash Strategic. That's Oracle dot com slash Strategic Oracle dot com slash Strategic.
If you love iPhone, you'll love Apple Card. It's the credit card designed for iPhone. It gives you unlimited daily cash back that can earn four point four zero percent annual percentage yield. When you open a high Yield savings account through Applecard, apply for Applecard in the wallet app, subject to credit approval. Savings is available to Applecard owners subject to eligibility. Apple Card and Savings by Goldman Sachs Bank USA Salt Lake City Branch Member FDIC terms and more at applecard dot com. When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt. You're probably not thinking about the environmental impact of each and every bite, but the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty fifty. That's why they're working hard every day to find new ways to reduce waste and serve natural resources and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US Dairy tackling greenhouse gases. Many farms use anaerobic digestors that turn the methane from maneuver into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza or lick an ice cream cone, know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit us dairy dot com slash sustainability to learn more.
All right, we're talking about the speed of light, causality the universe, and light cones, which are sort of like a visualization in physics that help you kind of figure out what you can't affect and what you cannot affect, because I guess if something is far enough away, you can't affect it right now, right because you have to wait for the speed of light to get from here, there or there to hear.
It doesn't even have to be far away. Something that's one foot away from you, like literally one foot away from you right now, you can have no influence on what's happening right there, right now, because even if you shot your death ray, it would only affect what's happening a foot away from you. In the time it takes for light to travel from the tip of your deathray one foot. There's nothing you can do about what's happening one foot away from you right now.
Oh wow, that's kind of weird, right to know that there's stuff around me that is unaccessible to me.
Yeah. I mean, even though if you're seeing something that happens a foot away from you, that means it actually happened in the past, so it's already done anyway, right, So all you can do is affect the future, right, That seems obvious. But you also can't affect the future everywhere, Like if you want to change the future of Andromeda, you know intuitively you can't change the future of Andromeda tomorrow or the next day or even the next year. It would take millions of years for any decision you make to affect anything in Andromeda, because nothing you do will get there. No choices you make can propagate that far before a million years, because it's a million light years away.
Right, Yeah, I guess that's the big consequence of having a speed limit in the universe. It is this idea that you know there are things in the present, but you can't really touch them or affect them or even know what they are right now in the same present as you.
That's right. There's a limit on the information and how information travels. It's really fascinating. You can only ever see one slice of the universe, and your slice of the universe might tell a different story from other slices of the universe. And this is really hard to get into your head because you imagine that what we're doing with physics is trying to build up like an absolute picture of the universe, like what's really out there, what is really going on, what happened in the universe, and what's going to happen, And it's hard to accept that one you can never really know everything about what's going on in the universe because you're limited to the slice of information you're going to get, but also that what you do learn about the universe might not be like the absolute truth. It might just be like what things look like from your perspective, right.
I think we talked about this once in the podcast. It's like, imagine like how the human society was before the internet or before telecommunications, you know, when we had to rely on writing letters and you know, waiting for newspaper to be delivered to your door. It's like, there could be things happening right now in other parts of the Earth, but you know it'll be a long time before you find out about them, or you know that they actually happened at the same time that they happen.
That's right, and speeding up our communications has sort of expanded our cone of understanding. Right, It's shrunk the time it gets for information to get here, but not too zero. Even with cell phones and speed of light electronics, you still can't know exactly what's happening across the world right now. There's still a time delay. And that's why it's cool to see in some of these TV shows that they really incorporate that you know that if you're trying to coordinate your army on Mars from your base on Earth, it takes time for your messages to get there. If this battle going on around you know, the atmosphere of Jupiter, that by the time you've heard about a beginning, it's probably over already and there's nothing you can do to change the outcome.
I guess like before, when you had a battlely you had to like send a messenger or send a scout or something you had, there was just huge delay, and so now things are faster, but there's still limited, like there's still no simultaneity, Like there's still no ability to know what is going on right now somewhere else.
Yeah, exactly. And the same concept this light cone, which tells you, like what you can influence, it also works in the other direction. You have like a backwards light cone. If you think in the other direction, like how close does somebody have to be to me to shoot a death ray and hit me right now. You know, if somebody is in Andromeda and they shoot a death ray at you, you're safe for a few million years, right Nobody in Andromeda can kill you right now. Even if they shot their death ray one hundred thousand years ago and it's been hurtling towards you for one hundred thousand years, you're still safe. It's not going to get here for a while because they are not in your backwards light cone yet.
But if they shot it a million years ago, it would be hitting us right now potentially. And if they shoot it right now, they were still going to get hit, but it's going to be a million years from.
Now, that's right. If they shoot it right now, it's not in our past light cone, but our past light cone moves up this time access and eventually they will be inside our past light cone, and yes, it will get here right but you're safe right now. Right now, there's this past light cone that dictates all the things that could be influencing what's happening at your location, and somebody really far away or even a foot away, can't influence what's happening to you right now. They can only influence your future.
Right well, they can't influence you right now. But I mean, it doesn't mean you're safe from a death ray, because they could have shot it a while ago and you would still die from the death ray arriving now.
You're right, And the weirdest thing, the worst thing about death rays is that they travel at the fastest speed possible, so there's literally no way to get any warning. Right the moment you see it is the moment it arrives, the moment it impacts you.
But hopefully, you know, a million years ago, you know, we were just cave men and women, and you know we didn't do anything to Offendi's.
Agents, hopefully, Or maybe it's a natural process, maybe the gamma rays from a supernova that blew up you know, a while ago, and those sterilizing death rays are just now arriving here at Earth.
Man, this like cone makes me feel not at all safer, Daniel, I see how you can draw comfort from this light cone. It's like a pretty flimsy protection against giant gamma ray bers.
It just means that somebody's got a plan ahead. If they really want to fry us now, they're got to either be close by or they have that planned ahead.
So that that's exploding. Start are you saying it's not very good at planning so we're saved? Is that it's a procrastinator.
It saves us from procrastinators exactly.
But what about type A supernovas? Oh, the kind of plants ahead.
There's nothing we can do.
Yeah, we're toast all right, So it sort of protects us, and I think it also kind of affects what we might agree on.
Is kind of a consistent history of the universe, right, Yeah, it's really interesting. The whole universe can be divided into three regions. You have your future like cone, your past like cone, and then there's everything else, right, And physicists call this the absolute elsewhere. It sounds like an awesome name for a Netflix show or something. So the absolute elsewhere is the spot that you can't affect, you can't influence, right, And that's really interesting because things that happen in the absolute elsewhere, you might disagree with people about the order in which they happen. Like you might look at a series of events and say A happens before B, and somebody else might look at it and say, no, No, I think B happens before A and you could both be right. If these two things are not inside each other's like cones, so these events don't have overlapping like cones, then they can be differently ordered and not affect anything from a causality point.
You WHOA, So I guess I can have a light cone and you can have a light cone. And if those two don't interact, what do you mean like if they don't touch, then we were looking at literally like different universes.
Well, they will eventually touch, right, because their light cones will eventually impact, and so there is some overlap in their light cone far in the future where both of them can influence. But it doesn't matter which one happened first, Right, It doesn't matter if A happen and then B or B happened and then A. And because these two events are the events themselves are not inside each other's l like cones. Right, B is not in a's like cone, and A is not in b's like cone. Even though the two light cones do overlap, if they are not inside each other's like cones, then you can swap their order just by changing your speed. If you decide to zip by them in a spaceship that's close to the speed of light, you will see one happen before the other, and if you go in the other direction at nearly the speed of light, you will see the opposite order of events. And it all works out downstream. Because these two things aren't causally linked. They're not inside each other's light cones, so you're free to change their order of events.
But then you know, the two of you who are involved would have a different interpretation, right, Like one of them will see one thing happening before the other.
Yeah, exactly, but there is no absolute definition of what happened. First, all the observers have their own interpretation, and they're all correct because the answer depends on your position. That's not true for two events where one is inside the other one's light cone. If I shoot a joke ray and I hit you in the head, then you laugh, right.
Put it on joke mode. Please, there's dead it's fun, and then there's joke.
Right, it'll put it on banana mode. So I hit the ray and the banana hits you in the head. Right now, you are in my light cone. Because the two events me pressing the button on the gun and you having a banana arrived in your mouth. They're not at the same time. What happens before the other, and there's a causal structure for them. I have to press the button before the banana ray arrives at your head. And that's okay, because the banana arriving at your head is an event in my future. It's inside my light code. But for example, you and I both have these guns and we point them in random directions or whatever, and we try to fire them at the same time. Some people might say we fired them at the same time. Other people flying by the spaceship might disagree about who pressed their trigger first.
Right, because they would be moving, and because of the way that light, how long light takes to get to them, and the speed limit of the universe, they might reconstruct the events in a different way.
Yeah, but it's not just because how long light takes to get to them. Even if you factor that in, right, if you account for how long it takes the signals and the images to appear, there's still a difference in the order of events. And that's because time flows differently based on where you are and how fast you are going, So your speed affects how you see time. Flowing, and so you can see one event happening before the other. You can see Jorge presses button first, or somebody else going in the other direction can see Daniel press their button first, even if they account for the trendsit mission delay from light.
But they would be wrong, I guess what I mean. They would have their own interpretation, but other people would have their different interpretation.
Yeah, but nobody's right or everybody's right. You know, if these two events are not inside each other's light cones, right, their light cones can overlap in the future. But if the two events themselves are not inside each other's light cones, then their order is not well defined.
And this is all because the universe has a speed limit, right, Like if it didn't have a speed limit, then you could talk about like an absolute history of the universe.
That's right, exactly, And that speed limit defines the size of this cone. Right. Imagine, for example, if the speed of light was much much slower, then your light cone would be narrower. The part of the universe, the part of the future that you could influence, would be a much smaller part of the universe. If you shot death rays in every direction and the speed of light was much smaller, then you would kill a smaller fraction of the universe. Or if you shot joke rays, you would make a smaller fraction in the universe laugh. Then if the speed of light was ten times faster than it is, the influence more of the universe and aliens out there with their joke rais could make us laugh more effectively. So this number the speed of light really changes the whole structure of causality of space.
Right, but what if you make like a light joke like.
This vanilla is the best ha ha, that's a joke.
Like a light vanilla joke. Yeah, that wouldn't harm anyone and people would just let it go by. But it really is sort of like a cone. I'm thinking like a dog cone. You know those cones they put on dogs, yes, so that they don't harm themselves or just to protect them. It really is like a cone that you put on our we put on our heads that kind of limit what we can see and what we can interact with, right.
It sort of does. Now I'm imagining you with one of these on your head trying to eat a banana even though you can't get it.
I'd be like Daniel, shoot me with the banana, shoot me exactly.
Then you need me to shoot you with the banana.
Ray or I could shoot one up in the air and then catch it, and the cone would help me catch this.
There you go. There you go pretty soon to be surrounded with bananas.
I'd have a cone around my head, filmed with banana, and.
I'll come along with a scoop of vanilla on top.
There you go.
And then, But the amazing thing to me is that we still don't know why the speed of light is this number. You know, it has such a dramatic effect on what part of the universe we can see, and what part of the universe we can influence, and how the universe is sort of like tied together, you know what effects what It really changes everything, And it's just like a number we measure it. We don't know why it is what it is. It could have been bigger, it could have been smaller, for all we know. Our laws of physics just have like an empty spot there. I feel like, right in the number you measure, there's no reason it has to be this or that that we know of. And that's like a real mystery, you know. It makes you wonder why it's this and not something else.
All right, cool, Well, let's get into now what consequences is this light cone has in the universe and possibly in our ability to travel through time. But first, let's take another quick break.
When you pop a piece of cheese into your mouth or enjoy a rich spoonful of Greek yogurt, you're probably not thinking about the environmental impact of each and every bite. But the people in the dairy industry are. US Dairy has set themselves some ambitious sustainability goals, including being greenhouse gas neutral by twenty to fifty. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. Take water, for example, most dairy farms reuse water up to four times the same water cools the milk, cleans equipment, washes the barn, and irrigates the crops. How is US dairy tackling greenhouse gases? Many farms use anaerobic digestors that turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. So the next time you grab a slice of pizza, or lick an ice cream cone. Know that dairy farmers and processors around the country are using the latest practices and innovations to provide the nutrient dense dairy products we love with less of an impact. Visit usdairy dot com slash sustainability to learn more.
There are children, friends, and families walking, riding, passing the roads every day. Remember they're real people with loved ones who need them to get home safely. Protect our cyclists and pedestrians because they're people too. Go safely California from the California Office of Traffic Safety and Caltrans.
Hey, there's Ryan Seacrests for Safeway. After a summer is spent enjoying the outdoors follows the perfect time to stock up on all your self care favorites for you and your entire family. Now through October first shop in store or online and safe when you purchase items like flown Aise allergy relief, Colgate toothpaste, addvil Kaplitz or Colgate toothbrushes, get back into your self care routine. Offer ends October First. Promotions may vary, restrictions apply. Visit safeway dot com for more details.
Plucky Land slots asking people, what's the weirdest place you've gotten lucky?
Lucky in line at the Delhi I guess ah, in my dentist's office more than once. Actually, do I have to say?
Yes?
You do?
In the car before my kids PTA meeting?
Really?
Yes, excuse me?
What's the weirdest place you've gotten lucky?
I never win and tell you have it.
You could get lucky anywhere playing at lucky landslots dot com.
Play for free right now?
Are you feeling lucky?
No purchase necessary veg't group would be preporit to buy low et plus terms and conditions apply.
All right.
We're talking about light codes and the speed of light and whether or not we can affect things in the universe that are happening right now, which is basically no, right, Like, we can't affect anything else in the universe happening at this moment.
That's right, nothing except for what's happening right here, right now, or stuff that's happening in the future. But at this very moment, you can't affect anything except for exactly the spot where you are.
Well, technically nothing, right because even things that are one millimeters away from my eye in the present moment I can't even see or effect.
That's true. We have to go down to zero millimeters. And that's even only if you believe in free will and if your brain operates instantaneously. So technically you're right. Any decision you make right now can only influence the.
Future, except that maybe there's a possibility to use this concept to do time travel, Daniel, so explain that to me.
Yes, So, what we talked about so far, this idea of light cones these circles of light expanding out into the universe and into your future. This is the way we think about space. If it's not curved, so we call space flat. If it's just sort of like has no shape to it, if there's no bending of it that affects like the path of photons. And we know that space can be bent. We know that, for example, everything with mass and energy bend space, like the Sun bends space. That's why the Earth is moving around it instead of just flying off into deep space. We know that you bend space because you have mass, and so everything out there changes the shape of space, which means it changes how light goes through it. Remember that gravity is not just like a force that tugs on things because light, for example, has no mass, but gravity can affect its path because gravity change which is the very shape of space, and light travels through that space. And so we know that things are more complicated when space gets curved. So what we've talked about so far is only in the event that the universe is empty and there's no curvature, there's no mass or anything that changes the shape. So in flat space, when there's a lot of mass around, things get curved and things get pretty different and weird. These light cones, which you can imagine sort of like going up and going down now start to get tilted.
Right. This is this something we can actually see, right, You can see light getting bent out there in space by heavy objects.
Yeah, it's called gravitational lensing. If there's like a really big heavy object between us and some source of light, like a background galaxy, then as those photons come towards Earth, they get bent around that massive object. And this is one way we can detect, for example, the existence of dark matter and try to figure out like roughly where it is based on how it distorts the light that's passing near it or through it. So it's definitely a real thing that's happening. It's something we've observed. We're sure it is true.
So if space can bend light, or bend space can sort of affect the trajectory of light, that would make sense that it would bend these light cones that we have to kind of figure out what we can't see and cannot see in.
The universe exactly, because the shape of the light cone is defined by where light goes right where light can reach, and so if space is bent in a way that light can't get somewhere, then the light cones are also bent. So this idea of them being like simple cones is only in flat space. Near something really massive, they bend towards the mass, right, because light moves towards mass. Right. If you have, for example, the Sun, and you shoot a photon near the Sun, it will get curved sort of in the direction of the Sun. And if you have a black hole, then it's going to get curved towards the black hole. So as you get closer and closer something massive, these light cones tilt more and more.
Whoa, they start to look like maybe horns and not so much cones.
Or yeah, or like bow ties or something yeah, or like bugle.
Do you remember that snack the little light cones curved cones. Yeah, exactly, Yeah, light bugles. We'll call it.
Light bugles exactly. And so inside a black hole, of course, you can think about what happens to a photon. Well, a photon inside a black hole always goes towards the center, not because gravity is so strong, but because the shape of space requires it, because there's only one direction inside a black hole. So inside a black hole, these things have tilted totally sideways. You shoot a photon and it goes just towards the singularity. All the light cones are now tilted towards the center. You hear people say sometimes this thing that inside a black hole, space and time switch rolls. Right. This is like a geometric way to understand that, because now instead of time flowing up, it's sort of flowing sideways, right, because the light cone has tilted over by forty five degrees.
WHOA, I guess I don't understand it at all. So the light cone tilts and somehow time and space switch decisions. Is that what you just said?
Yeah, because your future, all possible futures are the singularity, and so the only way to move forward in time is to move in this one direction of space, and so sort of like moving through space towards the singularity is the same thing as moving forwards in time. And you can graft that geometrically by thinking about the light zone being tilted over from being vertical to being horizontal.
It's like there's only space and time become one way and everything goes in the same direction. Yeah, exactly, all right, And so then how does that relate to time travel? You said it might be possible to do time travel.
Yeah, it might be possible to do time travel. If you use these cones, you can construct this really weird structure, right, So we talked about how near something really heavy, these cones can tilt like up to forty five degrees right towards like the center of a black hole. Now, imagine if you could have a cone that tilted more than forty five degrees, And what that means is that you're tilting so that part of the light cone is now in the past, right, So it's possible if you could do this, it would mean that these particles are moving not just into the future, but like the future is now dipping into the past.
What you mean you bend the light cone so much it wraps around and touches kind of the past light cone.
Mm hmm exactly, And you think, is this possible? Does not contradict itself? Well, remember that, like the definition of time and the definition of space depends a little bit on how fast you're going and the environment you're in, and that gets even more complicated when space is bent. And so what you can have is like a particle moving forward into its future, like its local time still says I'm moving forward in the future one second, then the next second, then the next second, but it could be moving into the past from the point of view of another observer. So like from a distant observer who's watching this from far away, whose space isn't curved, they could see that particle moving into like their past, even though if it's still moving into its own future.
Whoa wait, are you saying that space and time actually curve around itself or it only looks curved around to a different observer.
Now, the structure of it is actually curved. And people think in some weird configurations, if there's a very special arrangement of mass, then you might be able to construct a structure of space that allows particles to have their local future, their personal timeline extend into like the past from the point of view of other observers.
Oh, from the point of view of other observers, But the particle itself wouldn't be traveling into the past, or like me, I wouldn't be traveling into the past.
Well, it's like into their own future. But that's sort of like what happens on a time travel show. Right. If you are on a time travel show and you want to go into the past, you're still living your life forward on your timeline. Right, you were forty six years old in seven days and two minutes, and then when you go into the past, you're not like younger again, right, You're just like keep going forward. Now you're forty seven years, two days and five minutes and seven minutes and ten minutes. So what you want is your own timeline to continue, but you want the structure of space around you to change so that your timeline, your future now goes into like the rest of the universe's past. So this is called in physics, it's called a closed timelike curve because if you can till a bunch of these cones just the right way, then you can make this path that loops on around itself and comes back to the same point where it originated. So it's like shooting a light beam and having it hit you in the back of.
The head, almost like a wormhole kind of in time.
Almost like a wormhole. Yeah, it's not actually a wormhole, because a wormhole is like a shortcut between two distant locations. This is like a structure in space. It's like a loop in space time, right. It is a complicated reconnection and rearrangement of how space works, But it's technically a little bit different from.
A wormhole, right, wouldn't you be stuck in this loop like you'd it'd be like groundhogs day for this particle. It'd just be reliving, going around and around and around. It thinks it's going in the future, but really it's like revisiting the same time over and over and over.
Exactly. It's a structure that reinforces itself, and it's only stable if it does revisit itself. And so you're right, you wouldn't like to get to go back and choose a different flavor of ice cream or set your death ray to banana instead of death right, you have to make the same choices over and over again. It's like this self supporting structure in space and time so not recommended.
Well, unless you want to keep watching the same shows maybe, or if you really like vanilla and you want to eat only vanilla flavor for the rest of your lives for eternity.
Yeah, exactly. And this is something which is theoretically conceivable, like people have worked this out on paper and it seems like it might work. But again, general relativity doesn't tell us like how to bend space to make this happen. People are like, if you could bend space in this particular way, then we think this could happen. That doesn't mean necessarily we know how to make space bend in that particular way. You know. People have ideas, they have this crazy structure that's like an infinite spinning cylinder of dust, and they do the calculations. They think maybe that would allow for these closed timeline curves to happen. But other people think it's impossible, there's no way it could work, and that we have to just sort of throw up our hands and say, let's figure it out. When we get the unified theory of everything.
Well, you're saying that it according to the equations, it's possible, or like you know, anything that can bend, if you bend it enough, this will happen. But we don't know if it's physically possible to do it.
We don't know if it's physically possible. If you believe general relativity is absolutely true and you can construct an infinite spinning cylinder of dust, then you should believe this is physically possible and can actually happen. Personally, I don't think general relativity is a true theory of nature because it ignores quantum mechanics, and so it can't be correct. And we need some updated version. And it might be that in that updated version and incorporates quantum mechanics, this doesn't work anymore. So this could be like sort of like a singularity of a black hole, like a sign that the theory is wrong because it predicts this sort of nonsense result.
Right, because I guess if it's a closed loop, how would you even get into that loop? Right?
Yeah, you have to have somebody else build that infinite spinding cylinder for you in the infinite past, because you'll always be in that loop.
So it might exist and there might be a particle stuck in it or from the beginning of time, but you wouldn't be able to get in or out of it.
That's right. If it exists, it would be stuck sort of forever. But you know, now we're talking about like construction of a time loop, so we're talking about the variation of the loop as a function of time. So it's like an extra level of meta time there, which gets tricky.
You can't just use the same vanilla equations. You get to go extra spicy or sprinkle some bugles on for some extra crunchiness. All right, So that's the like one I guess, and I guess you're saying. It's one way that it helps you think about all these weird situations of space and black holes and bending time and space time looping around itself. You use that in your everyday you know, theoretical mus I do.
And also when people write to me and they ask me some like crazy question about special relativity involving you know, spaceships and snowballs whatever, I usually end up drawing like cones so I can understand, like, well, this happened there. What will this person see or is it possible for them to know this. It's just a nice way to sort of like separate things because in physics problems because much simpler when you can separate and say these things are independent from those things, so I can just deal with it on its own. They're not like entangled. So like cone shows you how to like disentangle all the causal threads of the universe into a bunch of different packets.
Right, Yeah, everything's better with the snow cone.
That's our next episode. What is a physics snow cone?
It's a cone where physicis you says no all the time, It's no. Can I travel back in time? Snow?
Yes?
All right, Well, hopefully it helps all of you out there think about causality and what we can and cannot effect about the present and maybe makes you appreciate a little bit more where you are and what we're able to see of this big, crazy universe. Well, thanks for joining us, see you next time.
Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows.
Have you boosted your business with Lenovo Pro yet. Become a Lenovo Pro member for free today and unlock access to Lenovo's exclusive business store for technology expert advisors and essential products and services designed just for you. Visit Lenovo dot com slash Lenovo Pro to sign up up for free. That's Lenovo dot com slash Lenovo Pro. Lenovo unlock new AI experiences with Lenovo's think Pad x one carbon powered by Intel Core ultraprocessors.
When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases. Many farms use anaerobic digestors to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last Sustainability to learn more.
There are children, friends, and families walking riding on paths and roads every day. Remember they're real people with loved ones who need them to.
Get home safely.
Protect our cyclists and pedestrians because they're people too. Go safely, California from the California Office of Traffic Safety and Caltrans
