WEBVTT

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For

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six years ago we did an episode about the speed of light and why we can't travel that fast.

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Now it's still high time.

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att göra en fortsättning på det avsnittet och prata om hur vi ska göra då om vi vill ta oss ljusår bort utan att behöva frysa ner oss och spendera tiotusentals år på ett generationsskett.

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Mm,

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och det visade sig att det räckte inte riktigt med ett avsnitt för att förklara det här.

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Nej,

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vi fick det lite i två delar.

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Först lite tid och rum och sånt.

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Och så fortsätter vi i nästa avsnitt med självaste resan i...

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Ja,

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och tiden går,

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så det är bara att dra igång här.

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Jag heter Susanna Levenhaupt.

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Jag heter Marcus Pettersson.

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Och du lyssnar på

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Har vi åkt till Mars än?

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Okej,

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så nästa avsnitt kommer att handla om maskhål och tipsresor.

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And to make it easier to understand,

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we have some other things to keep an eye on.

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Yes,

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the speed of light,

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for example.

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It's 299,792,458 meters per second.

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That's about 300 million meters per second.

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That's

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300,000 kilometers per second in vacuum.

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Do you want to put it in perspective?

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And like four and a half laps around the Earth in one second?

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That fast?

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And time?

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What is that?

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Well,

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you could think it's a simple thing,

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but not.

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So before we start talking about time travel and travel through mass holes that can move us light years in just seconds,

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let's start from the beginning.

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Sören Holst,

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university lecturer in theoretical music at Stockholm University.

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What is time?

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You can answer that question in different ways,

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but the easiest answer is to say that time is what you measure with a clock.

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And that might sound a little trivial,

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but it's actually more deep-seated than you might think.

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But the other answer that you can also give,

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and that is also deeper than it sounds,

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is that time is one of the dimensions in space-time.

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And space-time is...

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both space and time as one unit.

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And one can say that the basic insight in

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Einstein's special relativity theory is that one cannot see space and time as separate,

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but that one must see them as one unit,

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which we call space-time.

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And time is one of those dimensions.

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Yes,

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and it was also Einstein who said that the easiest way to explain time is to measure it with a clock.

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Yes,

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exactly.

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But you also told me when we talked earlier that my clock doesn't have to go in the same tempo as your clock.

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No,

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so that's also one of the core insights here in the special relativity theory.

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And it sounds very strange if you have,

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so to speak,

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a Newtonian picture of space and time,

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that is,

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the picture that also rotted in physics before relativity theory,

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before Einstein came up with his relativity theory.

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Then you thought,

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even in physics...

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That time is something universal,

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it's the same for everyone,

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it's ticking on no matter what we do,

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what we are somewhere in the universe.

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It's what drives the scenes forward,

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and it's universal and absolute.

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And I think it's just in contrast to what Einstein says,

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that time is what we measure with a clock,

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to get away from this idea of the absolute universal time that Newton thinks of.

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Einstein says,

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well...

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We shouldn't think of a universal time,

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but think that time is what you measure on your clock.

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And that insight in combination with the fundamental thing here is space-time as a whole.

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That makes it a little less strange that time can go differently fast depending on how you move.

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And actually also a bit dependent on where you are in the universe.

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But let's keep in mind that time may depend on its movement.

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There are several ways to understand why it is so.

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And one way is to connect it with the speed of light,

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which I know you've talked about earlier.

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And...

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Then you might feel that the speed of light is universal.

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It's the same speed for everyone.

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So no matter who measures the speed of light,

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you get the same value.

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It's also the case that the speed of light is a max speed,

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so nothing can move faster than the speed of light.

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But if we focus on this strange condition that whoever measures the speed of light in a vacuum gets the same value.

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By the way,

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what is that value?

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Do you remember that?

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299

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000.

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Something.

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Yes,

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exactly.

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Good.

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Kilometers per second.

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Exactly.

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Okay,

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but the point now is that the speed is the same for everyone who measures it.

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And that actually has a lot to do with the fact that time goes differently quickly depending on how we move.

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Because you can express it in different ways.

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The reason that the speed of light can be the same for all observers is simply that our clocks go differently depending on...

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So if a light pulse passes us here in the studio,

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and you Marcus decide to try to go past this light pulse,

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so you set off in the same direction as the light pulse in your super fast spaceship,

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then the claim is that you will still think that the light pulse is decreasing with the speed of light.

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How fast you even move,

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even if you move at 99%

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of the speed of light,

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you will think that the light is decreasing from you.

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So if you move at 99%

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of the speed of light,

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you will think that the light is decreasing

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with the speed of light.

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The reason is that it can be that your clocks go slower than mine and Susannas studio clock here,

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when you move.

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Exactly.

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So if we say that I can go 99.9%

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of the speed of light,

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and then

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I look at the light and it moves away from me...

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In the speed of light.

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The difference is 0.1%.

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And then my clock goes 0.1%

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of the speed that yours does.

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Yes,

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almost.

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Say yes.

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There is a complication.

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It's not just the time that goes differently when you move.

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The lines you measure up also become different in a corresponding way.

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If you want to express it completely correctly,

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you should take into account that as well.

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But if we move away from that complication,

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it's about as you say.

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I thought it felt nice.

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Do you know what a reasonable explanation is?

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Yes.

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So then we can,

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we take that,

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we say that it's true.

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Yes,

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so let me try to make an analogy.

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So,

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so let's skip time first.

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Just think of the room.

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Think,

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think,

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think of the studio table in here.

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Consider two points on the studio table.

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You can draw a lot of different curves between those two points on the studio table.

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and those curves are different lengths,

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of course.

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And it's clear that the straightest path between two different points on the table is the shortest path,

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right?

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Yes.

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So if you first draw a straight line and measure how long it is,

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then it has a certain length.

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If you then make a crooked line,

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then it will be longer.

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Okay.

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Now,

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Marcus,

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we can imagine that you would ask me now,

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why is it that the crooked line becomes longer?

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But I understand that.

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Yes,

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but the question is if you do that.

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The question is if you don't just feel that you understand it,

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because you're so used to it being like that.

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The reason it's like that is that this study table has a certain geometry.

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It's about some geometric laws here that say it's like that.

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And the answer when it comes to space-time,

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and that time can go differently depending on how you move,

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is actually completely analogous.

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Space-time has a geometry.

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that light has these characteristics and time has these characteristics.

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And there are a lot of other characteristics too.

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But if we do it more concretely,

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then we say that we look at a space journey.

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Okay,

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so Susanna,

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we say that you take off in a super fast spaceship.

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And me and Marcus,

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we sit and wait for you here in the studio.

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And our studio clocks are ticking here somehow.

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So you leave,

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on a long journey,

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and then you come back.

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It may have been a few days here,

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we have been sitting and waiting for you for a few days in the studio when you came back.

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Then we can say that the event when you left us,

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it's one point in the room time.

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The event when you came back to us,

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it's another point in the room time.

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You're back to the same point in the room,

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namely the studio,

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but it's a different time,

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so it's a different point in the room time.

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Yes,

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and Marcus,

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we've been sitting here and waiting for you all the time,

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so we can say that we've moved on a straight line in the room time.

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But you've moved on a crooked line in the room time,

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because you've moved away from us first and then back.

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So if we were to draw this in the room time,

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in some way,

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it would be...

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A curvy line that you've moved around in the time.

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And the time along your line is different than the time along our line.

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Very analogous in fact,

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that the distance in the room is different depending on which curve you take between two points.

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So there is one important difference here,

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and that is that when you come back,

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say that it has been,

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what did I say,

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a couple of days for us.

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We've been sitting here waiting for two days.

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When you come back,

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say that it might have only been a few hours for you.

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That's what it could be if you moved at a speed close to the speed of light.

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The closer to the speed of light you moved,

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the greater the effect would be,

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that is,

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the shorter the time would have been for you.

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So you've moved on a crooked line in the room time,

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and it's shorter than the straight line that Marcus and I have moved on.

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So the difference is that the space-time has a different kind of geometry than the space.

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And the fact is that one can express the core in the special relativity theory in this way,

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by saying that in the space-time it is the case that the straight line between two points is the longest.

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So it's the opposite of the room,

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but it's still like that,

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it goes back to geometry,

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geometric properties.

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And now Marcus thinks,

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why does the room-time have that geometry?

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And the answer will be that we don't know.

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What Einstein discovered is that if you assume that the room-time has that geometry,

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then you can explain extremely many things in physics,

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which makes all modern physics today based on relativity theory and his insights on this.

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But we have no fundamental answer to why space-time has this strange geometry.

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Can you explain this with the distance?

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It also changed when I moved fast.

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Yes.

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If I go at 99.99999%

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of the light speed,

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the distance becomes shorter.

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Yes.

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Why?

262
00:12:12.217 --> 00:12:15.579
Then we have to ask ourselves what do you mean by the distance here?

263
00:12:15.619 --> 00:12:16.740
Because in space time,

264
00:12:16.820 --> 00:12:21.462
if you want to mark a distance between two points in space time,

265
00:12:21.522 --> 00:12:23.543
you have to talk about at what time both points meet.

266
00:12:23.583 --> 00:12:29.187
9.47 I go on a straight line at 99.999 the speed of light to

267
00:12:29.607 --> 00:12:30.467
Mars. And I know,

268
00:12:30.468 --> 00:12:32.168
a really stupid place for both points to move,

269
00:12:32.169 --> 00:12:33.669
but we assume that they stand still.

270
00:12:33.670 --> 00:12:33.729
Yes,

271
00:12:33.730 --> 00:12:33.829
we do.

272
00:12:33.830 --> 00:12:33.989
Exactly.

273
00:12:34.089 --> 00:12:35.610
But the question is,

274
00:12:35.630 --> 00:12:39.032
on your clock you can absolutely say,

275
00:12:39.132 --> 00:12:40.533
now the clock is this much.

276
00:12:41.089 --> 00:12:43.932
But if you're talking about the distance to Mars,

277
00:12:44.192 --> 00:12:49.396
then you want to ask yourself what time zone you're considering to compare with.

278
00:12:49.397 --> 00:12:50.838
Let's make an analogy.

279
00:12:51.338 --> 00:12:52.939
Say you're driving on the motorway.

280
00:12:53.160 --> 00:12:53.380
Okay,

281
00:12:53.381 --> 00:12:54.361
you have a car in front of you.

282
00:12:54.401 --> 00:12:59.505
You wonder how far the distance to the car in front of you is.

283
00:12:59.506 --> 00:12:59.725
I wonder.

284
00:12:59.726 --> 00:12:59.986
Yes,

285
00:13:00.026 --> 00:13:03.649
and you might think it's 10 meters.

286
00:13:04.661 --> 00:13:05.302
It's too short a pause.

287
00:13:05.303 --> 00:13:05.942
I was going to say that.

288
00:13:05.943 --> 00:13:08.544
The road is completely...

289
00:13:09.665 --> 00:13:10.585
Let me try it this way.

290
00:13:11.406 --> 00:13:13.087
Say that there's an explosion in the sun.

291
00:13:13.088 --> 00:13:15.209
Do you see it now?

292
00:13:15.210 --> 00:13:16.209
I say it in eight minutes.

293
00:13:16.349 --> 00:13:17.150
Exactly!

294
00:13:17.310 --> 00:13:18.411
That's right.

295
00:13:18.412 --> 00:13:21.113
So if you see it now,

296
00:13:21.193 --> 00:13:21.793
then you say,

297
00:13:21.794 --> 00:13:24.275
it happened eight minutes ago.

298
00:13:24.276 --> 00:13:25.556
And then you say,

299
00:13:25.557 --> 00:13:31.700
it happened at the same time as I drank a cup of coffee eight minutes ago.

300
00:13:31.701 --> 00:13:32.821
That's a concept of simultaneity.

301
00:13:32.881 --> 00:13:42.407
You have connected different times on the sun with different times on the earth and said that the explosion happened at the same time I drank a cup of coffee eight minutes ago.

302
00:13:42.707 --> 00:13:43.367
But I see it now.

303
00:13:43.368 --> 00:13:44.408
You see it now,

304
00:13:44.488 --> 00:13:45.729
exactly.

305
00:13:45.769 --> 00:13:56.215
Someone who passes you and the sun in a super fast space-travel won't think that those two points are simultaneous.

306
00:13:56.216 --> 00:13:57.095
And therefore,

307
00:13:57.135 --> 00:14:00.037
that person will also measure another distance between...

308
00:14:00.545 --> 00:14:02.126
Jorden och solen än vad du gör.

309
00:14:02.687 --> 00:14:08.512
Kommer den personen att uppfatta att det sker samtidigt som Marcus ser?

310
00:14:09.052 --> 00:14:17.099
Alla kommer vi överens om att det finns en händelse när Marcus ser explosionen och det finns en annan händelse när explosionen äger rum.

311
00:14:17.219 --> 00:14:19.781
Och det finns en tredje händelse när Marcus dricker kaffe.

312
00:14:20.521 --> 00:14:27.887
Men man kommer vara lite oeniga om vilka tids- och rumskoordinater man ska fästa på de där händelserna.

313
00:14:28.308 --> 00:14:30.049
Och det är det som gör att...

314
00:14:30.169 --> 00:14:33.532
The distance is different depending on who measures them.

315
00:14:33.632 --> 00:14:38.277
You use different conventions for your coordinates.

316
00:14:38.397 --> 00:14:40.519
How to divide the room time into room and time,

317
00:14:40.520 --> 00:14:40.940
you could say.

318
00:14:40.941 --> 00:14:41.420
Right.

319
00:14:41.421 --> 00:14:45.084
And since the solar radiation goes in the speed of light,

320
00:14:45.085 --> 00:14:47.626
it's everywhere at the same time.

321
00:14:47.747 --> 00:14:53.192
But it only goes in 99.999%

322
00:14:53.193 --> 00:14:54.073
of the speed of light.

323
00:14:55.470 --> 00:14:57.212
then it's not really everywhere at the same time.

324
00:14:57.312 --> 00:14:57.472
Yes,

325
00:14:57.512 --> 00:14:58.293
that's right.

326
00:14:58.294 --> 00:14:59.674
But the time before it is very short.

327
00:14:59.734 --> 00:15:00.455
Exactly.

328
00:15:00.555 --> 00:15:01.677
Which means that as it is connected,

329
00:15:01.678 --> 00:15:02.838
the distance is also short.

330
00:15:02.858 --> 00:15:03.018
Yes,

331
00:15:03.038 --> 00:15:03.739
that's right.

332
00:15:04.227 --> 00:15:07.788
Why didn't you say that?

333
00:15:07.908 --> 00:15:08.088
Yeah,

334
00:15:08.089 --> 00:15:11.749
so it's for an extra complication layer to measure distance.

335
00:15:11.750 --> 00:15:12.869
It's easier to keep it to...

336
00:15:12.870 --> 00:15:18.991
It's easier to keep it to just measure the time that flows on one's own clock.

337
00:15:18.992 --> 00:15:19.411
Can I just ask,

338
00:15:19.431 --> 00:15:21.392
because we're talking about room time,

339
00:15:21.393 --> 00:15:22.872
we're talking about room and we're talking about time.

340
00:15:22.873 --> 00:15:26.773
I understand how to measure time and I understand how to measure room.

341
00:15:27.113 --> 00:15:30.554
But what do you measure room time in for unity?

342
00:15:30.555 --> 00:15:33.955
I would say that you measure distance in room time on your clock.

343
00:15:34.115 --> 00:15:35.656
As time?

344
00:15:35.657 --> 00:15:35.736
Yes.

345
00:15:35.737 --> 00:15:42.422
The fact is that even spatial distances can be measured as time.

346
00:15:42.423 --> 00:15:51.370
And we do that when we talk about how many light years it is somewhere.

347
00:15:51.371 --> 00:15:52.811
If I say that it is four light years to

348
00:15:53.572 --> 00:15:54.372
Alpha Centauri,

349
00:15:54.713 --> 00:15:59.156
then it means that it takes the light four years to travel to Alpha Centauri.

350
00:15:59.176 --> 00:16:02.019
So I express a distance with a time.

351
00:16:02.743 --> 00:16:05.985
Given the fact that the speed of light is what it is,

352
00:16:06.345 --> 00:16:07.566
so to speak,

353
00:16:07.567 --> 00:16:10.448
we can actually express all distances as times.

354
00:16:10.449 --> 00:16:15.511
Distance between two spatial points,

355
00:16:15.512 --> 00:16:17.932
like distance from the Earth to a star somewhere,

356
00:16:17.952 --> 00:16:20.293
then we measure it in light years,

357
00:16:20.294 --> 00:16:20.554
that is,

358
00:16:20.555 --> 00:16:23.815
the time that the light takes to go there.

359
00:16:23.835 --> 00:16:28.798
If it is the time that flows between two time-like separated events,

360
00:16:28.818 --> 00:16:29.219
as they say,

361
00:16:29.220 --> 00:16:29.879
for example

362
00:16:29.899 --> 00:16:30.099
For example,

363
00:16:30.100 --> 00:16:34.482
when you left the studio and came back to your studio on your journey,

364
00:16:34.862 --> 00:16:36.784
we measure it with a clock,

365
00:16:36.884 --> 00:16:40.746
but in both cases we can express it as a time.

366
00:16:40.846 --> 00:16:41.107
Right,

367
00:16:41.147 --> 00:16:46.930
and that's when my time is different.

368
00:16:46.970 --> 00:16:47.111
Yes,

369
00:16:47.112 --> 00:16:47.611
it's shorter.

370
00:16:47.612 --> 00:16:52.814
You age less during your journey than when Marcus and I age here in the studio.

371
00:16:52.834 --> 00:16:59.659
In the beginning you were a bit concerned that time is also affected by time.

372
00:16:59.759 --> 00:17:02.220
of where we are.

373
00:17:02.240 --> 00:17:02.360
Yes,

374
00:17:02.420 --> 00:17:08.464
so what we have talked about so far is actually the special relativity theory.

375
00:17:08.544 --> 00:17:12.826
But Einstein has also come up with another relativity theory,

376
00:17:13.226 --> 00:17:15.167
namely the general relativity theory,

377
00:17:15.267 --> 00:17:17.609
which is Einstein's theory for gravitation,

378
00:17:18.289 --> 00:17:21.151
how gravitation works.

379
00:17:21.152 --> 00:17:27.834
And he explains gravitation by saying that space-time not only has this geometry we have talked about now,

380
00:17:28.034 --> 00:17:29.075
but also it is curved.

381
00:17:30.359 --> 00:17:32.000
It has an even more strange geometry.

382
00:17:32.600 --> 00:17:38.804
The extra component of the geometry of space-time explains the phenomenon of gravity.

383
00:17:38.805 --> 00:17:42.726
And that means,

384
00:17:42.766 --> 00:17:43.207
in turn,

385
00:17:43.208 --> 00:17:46.068
that in areas with very strong gravity,

386
00:17:46.108 --> 00:17:49.310
like at very heavy stars,

387
00:17:49.330 --> 00:17:50.611
or neutron stars,

388
00:17:50.612 --> 00:17:51.892
or even black holes,

389
00:17:52.392 --> 00:17:55.214
in the vicinity of them,

390
00:17:55.234 --> 00:17:57.355
space-time will be curved in such a way that

391
00:17:57.375 --> 00:18:04.599
That time goes very slowly for someone who is close to the neutron star or the black hole.

392
00:18:04.600 --> 00:18:07.301
So in that sense,

393
00:18:07.401 --> 00:18:10.462
time also goes differently quickly depending on where you are,

394
00:18:10.943 --> 00:18:13.024
how strong the gravitation is where you are,

395
00:18:13.244 --> 00:18:13.644
you can say.

396
00:18:13.664 --> 00:18:23.270
And it is so clear that it even gives effect if you are close to the surface of the earth or higher up from the earth.

397
00:18:23.271 --> 00:18:24.430
In principle,

398
00:18:24.431 --> 00:18:24.650
yes.

399
00:18:24.651 --> 00:18:25.251
In practice,

400
00:18:25.311 --> 00:18:25.431
no.

401
00:18:26.111 --> 00:18:26.451
Yes,

402
00:18:26.452 --> 00:18:27.672
you can measure the effect.

403
00:18:27.833 --> 00:18:29.054
It is extremely small.

404
00:18:29.055 --> 00:18:35.899
It actually has one practical allocation area,

405
00:18:35.900 --> 00:18:37.721
and that is this position determination system.

406
00:18:37.722 --> 00:18:41.384
You know that you determine your position via satellites.

407
00:18:42.565 --> 00:18:47.329
And the satellites are on a different height than what we do.

408
00:18:47.349 --> 00:18:51.913
And they also move in relation to us.

409
00:18:51.953 --> 00:18:54.175
And in order to be able to...

410
00:18:54.176 --> 00:18:54.235
Yes.

411
00:18:54.255 --> 00:19:00.060
The whole technique is based on the fact that you can compare time here on Earth with the time on board the satellites.

412
00:19:00.061 --> 00:19:08.968
And that makes both of these effects that we have talked about actually important for this system to work properly.

413
00:19:09.508 --> 00:19:15.833
So you have to take into account both that the clocks go too slowly in the satellites because the satellites move,

414
00:19:15.914 --> 00:19:21.939
and you have to take into account that the clocks in the satellites move faster.

415
00:19:22.727 --> 00:19:26.248
than on Earth because they are further away from Earth.

416
00:19:26.249 --> 00:19:28.369
Those two effects are in the same order of magnitude,

417
00:19:28.409 --> 00:19:29.629
but they are not really the same,

418
00:19:29.709 --> 00:19:30.869
they don't take each other out,

419
00:19:30.889 --> 00:19:34.010
so you have to take care of both for this GPS system,

420
00:19:34.150 --> 00:19:35.831
the position determination system,

421
00:19:35.911 --> 00:19:36.591
to work.

422
00:19:37.431 --> 00:19:37.711
Okay,

423
00:19:37.971 --> 00:19:40.172
we have a little bit of a hunch on what time it is.

424
00:19:40.173 --> 00:19:40.292
Yes,

425
00:19:41.152 --> 00:19:49.074
like half an hour into the conversation and we start to land on what time and room time it is.

426
00:19:49.094 --> 00:19:50.074
But that's good,

427
00:19:50.134 --> 00:19:51.595
that's really the basis.

428
00:19:52.135 --> 00:19:53.516
Then you walk away and understand the rest.

429
00:19:53.517 --> 00:19:53.617
Yes,

430
00:19:53.618 --> 00:19:54.758
this thing about traveling in time.

431
00:19:54.759 --> 00:19:55.979
That's right.

432
00:19:55.999 --> 00:19:56.520
Is it possible?

433
00:19:56.820 --> 00:19:57.601
Yes,

434
00:19:57.602 --> 00:20:02.466
if it is possible,

435
00:20:02.546 --> 00:20:04.728
you will find out in the next episode,

436
00:20:04.729 --> 00:20:06.490
which will be released in just a few days.

437
00:20:06.930 --> 00:20:08.731
Men spännande det där sista,

438
00:20:09.231 --> 00:20:14.272
om att hastighet och avstånd till jorden ger effekt på tiden i satelliter,

439
00:20:15.012 --> 00:20:18.613
som ju ligger ganska nära jorden och rör sig relativt sakta.

440
00:20:19.373 --> 00:20:22.174
Så då kan ni ju tänka er hur det är på längre avstånd,

441
00:20:22.434 --> 00:20:24.635
som miljontals ljusår,

442
00:20:25.035 --> 00:20:26.655
i höga hastigheter,

443
00:20:27.095 --> 00:20:28.356
som ljusets hastighet.

444
00:20:28.616 --> 00:20:28.736
Ja,

445
00:20:28.856 --> 00:20:30.937
alltså jag har jättesvårt att tänka mig det.

446
00:20:31.677 --> 00:20:34.517
Också lite svårt att tänka på det här som Sören nämnde,

447
00:20:34.698 --> 00:20:36.378
att avstånd krymper.

448
00:20:36.458 --> 00:20:37.999
when we move fast.

449
00:20:38.479 --> 00:20:42.461
It's like a perfect way to make this subject even more confusing.

450
00:20:43.442 --> 00:20:47.184
But now we have at least a little tip on what time is.

451
00:20:47.185 --> 00:20:49.285
And we're ready for the next episode,

452
00:20:49.305 --> 00:20:51.626
where we're going to talk about traveling in time.

453
00:20:52.067 --> 00:20:53.267
Absolutely,

454
00:20:53.467 --> 00:20:58.750
but before we learn to travel through time and space via mass holes,

455
00:20:58.751 --> 00:21:00.991
we have to stick to the usual way.

456
00:21:01.091 --> 00:21:04.273
Spacecrafts and rocket engines.

457
00:21:04.274 --> 00:21:05.494
And then we can use gravity.

458
00:21:05.994 --> 00:21:08.516
When we're going far out in the solar system,

459
00:21:09.176 --> 00:21:10.938
or like with Voyager 1 and 2,

460
00:21:10.998 --> 00:21:12.759
out of the solar system,

461
00:21:12.779 --> 00:21:18.383
it takes a very long time if you just accelerate with the engines.

462
00:21:18.544 --> 00:21:21.106
And the fuel easily runs out.

463
00:21:21.107 --> 00:21:23.607
But then you can use something called a gravitational slung,

464
00:21:24.128 --> 00:21:25.129
or gravity assist.

465
00:21:25.829 --> 00:21:30.533
You simply take the help of one of the planets on the way out to give the rocket a little extra push.

466
00:21:31.033 --> 00:21:32.174
René Laufer is...

467
00:21:32.274 --> 00:21:34.396
professor in space technology at

468
00:21:34.956 --> 00:21:37.999
Space Campus at Luleå Techniska Universitet.

469
00:21:38.519 --> 00:21:42.783
And we asked him to explain more about Gravity Assist and what we can do with it.

470
00:21:43.603 --> 00:21:46.686
Gravity Assist helps us save fuel.

471
00:21:47.146 --> 00:21:47.747
And that's great,

472
00:21:47.927 --> 00:21:52.150
because when we launch rockets and spacecraft into space,

473
00:21:52.651 --> 00:21:55.633
the majority of what we launch into space is fuel,

474
00:21:55.693 --> 00:21:56.154
basically.

475
00:21:56.294 --> 00:21:57.315
Rockets are 90%

476
00:21:57.435 --> 00:21:57.655
fuel.

477
00:21:57.895 --> 00:22:00.517
So if we can save fuel by going somewhere,

478
00:22:00.638 --> 00:22:01.118
that's great.

479
00:22:01.914 --> 00:22:04.856
One great way to do this is so-called gravity assist.

480
00:22:05.096 --> 00:22:11.520
So we use kind of a slingshot maneuver and we fly very close to a planetary body,

481
00:22:12.040 --> 00:22:12.900
the bigger the better,

482
00:22:13.001 --> 00:22:14.662
so Jupiter is wonderful actually,

483
00:22:15.422 --> 00:22:29.050
and then we get basically caught by the gravitational pull from this large body and this tiny spacecraft basically is thrown like a slingshot around the planetary body and thrown with...

484
00:22:29.310 --> 00:22:30.891
even higher velocity than before,

485
00:22:30.991 --> 00:22:33.812
further away from that planetary body.

486
00:22:33.872 --> 00:22:35.813
So that's the simple explanation.

487
00:22:36.793 --> 00:22:37.354
In reality,

488
00:22:37.434 --> 00:22:39.095
it's of course a little bit more complex.

489
00:22:39.415 --> 00:22:47.778
It's not so simple to fly precisely and so close to a body without crashing into something or having the wrong trajectory.

490
00:22:48.299 --> 00:22:50.200
But we have demonstrated this many times.

491
00:22:50.480 --> 00:22:53.181
The Pioneer 10 and 11 probes showed it already.

492
00:22:53.301 --> 00:22:55.302
Then the famous Voyager 1 and 2 probes.

493
00:22:56.062 --> 00:23:01.887
enabled with gravity assist to do this grand tour through the gas giants of the outer solar system.

494
00:23:03.068 --> 00:23:07.371
What we actually do is actually a little bit of energy transfer.

495
00:23:08.012 --> 00:23:16.999
So a little bit of the energy of this gigantic planetary body while it orbits the sun is basically transferred to this tiny spacecraft.

496
00:23:17.660 --> 00:23:22.043
And it has this tremendous effect because of this huge difference of mass.

497
00:23:22.544 --> 00:23:22.964
Jupiter,

498
00:23:24.245 --> 00:23:24.946
huge mass.

499
00:23:25.326 --> 00:23:25.686
You know,

500
00:23:26.127 --> 00:23:28.268
more than 100 times the mass of Earth,

501
00:23:28.549 --> 00:23:29.309
something like that,

502
00:23:29.690 --> 00:23:36.255
and this tiny little spacecraft that is maybe the mass of a little van or something like this.

503
00:23:36.715 --> 00:23:38.317
And when you fly close by,

504
00:23:38.397 --> 00:23:39.778
you transfer a little bit of energy,

505
00:23:39.918 --> 00:23:41.219
of the momentum,

506
00:23:41.539 --> 00:23:46.323
the energy of the planetary body moving in the solar system to this tiny little spacecraft,

507
00:23:46.683 --> 00:23:48.905
and that turns into additional velocity.

508
00:23:49.486 --> 00:23:50.887
So with the Voyager spacecrafts,

509
00:23:50.907 --> 00:23:54.690
we have seen that this was enough to increase every time.

510
00:23:55.434 --> 00:23:57.456
It flew by another planetary body,

511
00:23:58.216 --> 00:23:58.617
Jupiter,

512
00:23:59.037 --> 00:23:59.737
then Saturn,

513
00:24:00.118 --> 00:24:00.858
then Uranus,

514
00:24:01.058 --> 00:24:01.799
then Neptune,

515
00:24:02.540 --> 00:24:10.926
was enough to always increase the velocity and at the end of the day get enough velocity to even leave the solar system.

516
00:24:11.546 --> 00:24:15.950
And because you go so close to something that is like Jupiter,

517
00:24:16.050 --> 00:24:16.670
it's so big,

518
00:24:17.091 --> 00:24:18.612
it's lots and lots of gravity,

519
00:24:19.052 --> 00:24:21.114
how do you leave the planet?

520
00:24:21.514 --> 00:24:21.714
Well,

521
00:24:21.834 --> 00:24:22.234
actually,

522
00:24:22.394 --> 00:24:30.278
you are already on a trajectory that doesn't bring you into the situation that you become an orbiter of that planet.

523
00:24:30.738 --> 00:24:35.060
So to get really from one planetary body to another in spaceflight,

524
00:24:35.061 --> 00:24:35.340
you know,

525
00:24:35.420 --> 00:24:36.440
we launch from Earth.

526
00:24:36.821 --> 00:24:42.063
We accelerate enough to leave the Earth gravitational sphere of influence.

527
00:24:42.363 --> 00:24:43.743
Then we fly to another planet.

528
00:24:43.784 --> 00:24:44.164
And then,

529
00:24:44.264 --> 00:24:44.544
again,

530
00:24:44.564 --> 00:24:49.426
we do a maneuver that we basically transfer energy to...

531
00:24:50.338 --> 00:24:57.246
fly from a trajectory that would basically pass by another planetary body like Mars to enter an orbit around Mars.

532
00:24:57.587 --> 00:25:00.470
So there's always dedicated maneuvers that we do.

533
00:25:01.711 --> 00:25:05.295
It's a decision that we do and we fire an engine and things like this.

534
00:25:05.636 --> 00:25:09.260
So when we come to Jupiter and we do this the right way,

535
00:25:09.720 --> 00:25:11.481
Precise navigation is the key here.

536
00:25:11.962 --> 00:25:15.584
Then we don't end up in the orbit around Jupiter.

537
00:25:15.644 --> 00:25:18.106
We basically come to Jupiter,

538
00:25:18.726 --> 00:25:19.727
fly very fast,

539
00:25:19.787 --> 00:25:22.489
and then we are thrown like a slingshot further out,

540
00:25:22.889 --> 00:25:26.072
and we leave Jupiter faster than we came in.

541
00:25:26.832 --> 00:25:31.315
And then we are never entering an orbit around Jupiter.

542
00:25:31.756 --> 00:25:33.277
Could you do this around...

543
00:25:33.537 --> 00:25:33.817
I mean,

544
00:25:33.877 --> 00:25:34.537
Jupiter is big,

545
00:25:34.557 --> 00:25:35.658
but the Sun is bigger.

546
00:25:36.859 --> 00:25:37.980
Can we do it around the Sun?

547
00:25:38.488 --> 00:25:39.008
We can,

548
00:25:39.209 --> 00:25:42.591
and many people already thought about that and said,

549
00:25:42.671 --> 00:25:43.051
you know,

550
00:25:43.531 --> 00:25:46.854
one day when we want to have other probes,

551
00:25:47.334 --> 00:25:48.255
not human spaceflight,

552
00:25:48.475 --> 00:25:48.775
probes,

553
00:25:48.835 --> 00:25:49.656
robotic probes,

554
00:25:50.036 --> 00:25:54.099
that we want to get to the outer edges of our solar system even faster,

555
00:25:54.639 --> 00:26:00.223
we should not do it the way as it was done with the Voyager probes or with flying

556
00:26:00.563 --> 00:26:03.045
New Horizons to Pluto and further outwards.

557
00:26:03.785 --> 00:26:07.608
We should just first fly inwards and do this gravity assist.

558
00:26:07.908 --> 00:26:18.055
at the Sun and get such a huge slingshot trajectory that we are much faster at the edges of the solar system and shorten flight times.

559
00:26:18.355 --> 00:26:18.475
So,

560
00:26:18.555 --> 00:26:19.136
an example,

561
00:26:19.176 --> 00:26:20.356
if we want to explore,

562
00:26:20.436 --> 00:26:20.777
you know,

563
00:26:20.837 --> 00:26:27.081
the outer areas of our solar system or even have faster interstellar probes,

564
00:26:27.481 --> 00:26:29.382
then doing a slingshot at the Sun,

565
00:26:29.603 --> 00:26:31.804
a gravity assist in the Sun would be the way to do.

566
00:26:32.224 --> 00:26:34.146
And could we send something in,

567
00:26:34.206 --> 00:26:37.308
do a slingshot with the Sun and then also Jupiter on the way out?

568
00:26:37.388 --> 00:26:37.508
And

569
00:26:37.748 --> 00:26:38.248
Absolutely,

570
00:26:38.408 --> 00:26:38.908
absolutely.

571
00:26:39.028 --> 00:26:39.188
But,

572
00:26:39.328 --> 00:26:39.589
you know,

573
00:26:40.209 --> 00:26:41.589
it becomes more and more complex.

574
00:26:41.789 --> 00:26:43.650
So you have to plan very carefully.

575
00:26:44.630 --> 00:26:49.211
Maybe these opportunities are not available every month or every year.

576
00:26:49.471 --> 00:26:51.032
So with the Grand Tour,

577
00:26:51.112 --> 00:26:57.093
NASA really calculated very carefully and that is a once in a career type of chance.

578
00:26:57.614 --> 00:26:59.734
So the next generation can try this again,

579
00:26:59.794 --> 00:27:01.115
maybe something like this.

580
00:27:01.655 --> 00:27:02.715
But with the sun,

581
00:27:02.895 --> 00:27:03.355
of course,

582
00:27:03.375 --> 00:27:05.896
and then if Jupiter is at the right position.

583
00:27:06.668 --> 00:27:08.689
So the direction where you want to go anyway,

584
00:27:09.069 --> 00:27:12.331
then this is an opportunity to even gain more velocity.

585
00:27:13.511 --> 00:27:16.572
There's always a body that is bigger than you or your spacecraft.

586
00:27:16.933 --> 00:27:19.234
And how fast can you go?

587
00:27:19.394 --> 00:27:20.534
Which speeds can you gain?

588
00:27:21.134 --> 00:27:21.254
So,

589
00:27:21.895 --> 00:27:22.155
you know,

590
00:27:22.156 --> 00:27:23.335
in the spaceflight field,

591
00:27:23.336 --> 00:27:26.777
we often like to calculate in kilometers per second.

592
00:27:27.477 --> 00:27:29.818
And when we go into Earth orbit,

593
00:27:29.878 --> 00:27:33.740
we need to have the minimum velocity for an orbit around Earth.

594
00:27:34.088 --> 00:27:35.849
A little bit over 7 km per second,

595
00:27:35.869 --> 00:27:37.289
but when we launch with rockets,

596
00:27:37.810 --> 00:27:43.232
we often provide enough energy for more than 9 km per second because there are losses and stuff like this.

597
00:27:43.932 --> 00:27:47.574
When we want to fly away from Earth and it's more than 11,

598
00:27:47.614 --> 00:27:50.816
realistically more than 12 km per second and further down the road,

599
00:27:51.736 --> 00:27:54.377
we have reached velocities that exceeded...

600
00:27:55.210 --> 00:27:55.530
30,

601
00:27:56.011 --> 00:27:57.772
around 40 kilometers per second,

602
00:27:57.812 --> 00:27:59.073
if I remember correctly.

603
00:27:59.533 --> 00:28:01.014
But at the end of the day,

604
00:28:01.155 --> 00:28:05.958
it's just a matter of how close you want to get to that body that throws you outwards.

605
00:28:06.539 --> 00:28:10.461
And velocities more than that are certainly a possibility.

606
00:28:11.022 --> 00:28:13.544
So maybe somebody comes up with a very,

607
00:28:13.624 --> 00:28:14.605
very good trajectory,

608
00:28:14.885 --> 00:28:16.866
but gets very close to the sun and says,

609
00:28:17.267 --> 00:28:17.467
hey,

610
00:28:17.647 --> 00:28:19.348
we can do 80 kilometers per second,

611
00:28:19.349 --> 00:28:20.649
100 kilometers per second.

612
00:28:21.169 --> 00:28:21.530
And then...

613
00:28:21.930 --> 00:28:25.891
Getting to the outer edges of the solar system gets us much faster there.

614
00:28:26.371 --> 00:28:28.532
You don't have to wait your whole career to get there.

615
00:28:28.712 --> 00:28:29.372
When you do this,

616
00:28:30.073 --> 00:28:30.893
how do you aim?

617
00:28:31.473 --> 00:28:33.174
Interplanetary navigation is hard.

618
00:28:33.294 --> 00:28:34.534
There's no GPS out there,

619
00:28:34.634 --> 00:28:34.854
right?

620
00:28:35.014 --> 00:28:36.115
Once we leave Earth orbit,

621
00:28:36.155 --> 00:28:37.695
it's a bit more difficult.

622
00:28:38.135 --> 00:28:39.936
No precise navigation possible.

623
00:28:39.976 --> 00:28:41.816
But we learned a lot over the last 50,

624
00:28:41.896 --> 00:28:42.497
60 years.

625
00:28:43.897 --> 00:28:46.258
And we are able to do this.

626
00:28:46.358 --> 00:28:46.858
We use...

627
00:28:47.354 --> 00:28:48.755
Like back in the days with ships,

628
00:28:48.895 --> 00:28:50.495
we use optical navigation.

629
00:28:50.496 --> 00:28:51.436
We look at the stars,

630
00:28:51.456 --> 00:28:52.416
we triangulate.

631
00:28:53.417 --> 00:28:55.938
We use help from Earth,

632
00:28:56.298 --> 00:28:56.598
you know,

633
00:28:56.678 --> 00:29:00.780
with ground stations that send signals that help us with navigation,

634
00:29:00.820 --> 00:29:01.961
like we do this with planes.

635
00:29:02.581 --> 00:29:04.282
And there are many different ways.

636
00:29:04.342 --> 00:29:10.204
We even use catalogs of smaller objects like known asteroids because we know their trajectory,

637
00:29:10.264 --> 00:29:11.705
their orbits very precisely.

638
00:29:12.225 --> 00:29:13.766
They can help us to improve.

639
00:29:14.522 --> 00:29:18.445
and make our navigation better and our accuracy higher.

640
00:29:18.885 --> 00:29:20.546
So it's possible.

641
00:29:20.646 --> 00:29:21.367
We have done that.

642
00:29:21.407 --> 00:29:22.708
We have done that many times.

643
00:29:23.208 --> 00:29:27.611
We have very precisely flew by at even very small objects,

644
00:29:27.891 --> 00:29:29.312
like comets and asteroids,

645
00:29:29.372 --> 00:29:32.774
at very close distances of just a few dozens of kilometers,

646
00:29:32.775 --> 00:29:33.475
for example.

647
00:29:34.195 --> 00:29:34.315
So

648
00:29:35.036 --> 00:29:37.918
I think this is not so much of an issue.

649
00:29:38.118 --> 00:29:40.800
We can do that and we have the technical means for that.

650
00:29:46.167 --> 00:29:47.028
Spännande!

651
00:29:47.768 --> 00:29:50.130
Jag ser fram emot kommande avsnitt,

652
00:29:50.450 --> 00:29:54.953
då vi kommer fortsätta att prata helt andra rymdiga saker med René Laufer.

653
00:29:55.634 --> 00:29:58.056
Jag ser också fram emot nästa avsnitt,

654
00:29:58.416 --> 00:30:01.058
där vårt samtal med Sören Holst fortsätter,

655
00:30:01.438 --> 00:30:03.600
och vi gräver ner oss i maskhålen.

656
00:30:04.380 --> 00:30:07.702
Och i väntan på det kan ni göra en egen tidsresa,

657
00:30:08.023 --> 00:30:10.444
och gå tillbaka och lyssna på avsnitt fyra,

658
00:30:10.605 --> 00:30:12.546
där vi pratar mer om ljusets hastighet.

659
00:30:12.862 --> 00:30:14.162
And then in episode 32,

660
00:30:14.163 --> 00:30:17.843
where we talk about gravitation and black holes.

661
00:30:17.844 --> 00:30:21.424
A lot of good extra repetition to listen to before the trip.

662
00:30:21.444 --> 00:30:25.085
Another good thing to listen to is our music.

663
00:30:25.585 --> 00:30:30.427
It's written by Armin Pendek and is also available in the background on our website,

664
00:30:30.847 --> 00:30:34.528
havioaktimarsen.se My name is Marcus Pettersson.

665
00:30:34.588 --> 00:30:36.528
My name is Susanna Levenhaupt.

666
00:30:36.749 --> 00:30:41.990
Havioaktimarsen is made on Beppo by Rundfunk Media in collaboration with Saab.

667
00:31:00.312 --> 00:31:00.532
Hello,

668
00:31:00.572 --> 00:31:04.978
the program is made by Rundfunk Media.