[Music] [Applause] why can't we go faster than light because it makes space travel a little bit inconvenient yeah it does doesn't it it's a real shame cuz I don't know I grew up on Star Trek and yeah I think when I was a kid I sort of thought of Star Trek is being like a documentary about the future and and so I figured out okay there must be a way to go faster than light and then when I learned more physics I got pretty unhappy to be fair though I really really like the theory that
this comes out of the theory of relativity from Einstein if you try to get to the speed of light you know changing speeds requires force this is something that Newton pointed out Isaac Newton you know hundreds of years ago he said that you know an object in motion will stay in motion and an object at rest will stay at rest unless acted upon by an outside force so that you know an outside force with some source of energy is required to change your speed and if you want to change your speed a lot you need
more force and one of the things that relativity says is that if you want to get close to the speed of light it requires a lot more energy and in fact as you approach the speed of light it requires more and more and more energy and to get to the speed of light from any speed lower than the speed of light with any mass more than zero it requires an infinite amount of energy to get to the speed of light and of course if you want to go faster than light first you have to go
as fastest light yes so we don't have enough energy to go that fast it's impossible to have enough energy to go that fast that's disappointing yes anything like we can't go faster than light but can like anything else well so light can go as fast as light but to go faster than light relativity says that yeah if you're already going faster than light then you can go faster than light you can stay in that area and you can't it's it's the same sort of thing it's doomed to be stuck there if you're going faster than
light you can't go slower than light it would take an infinite amount of energy to take something going faster than light and slow it down in fact the the slower you make it go the more energy it takes which is really weird so if you it is so-so something going faster than light it's sort of low energy state is going instantaneously fast going infinitely fast from from anywhere to anywhere and it takes the the slower you want it to go the more energy you have to pump in and it would take an infinite amount of
energy to get it down to the speed of light this is already a reason to think that it would be really hard to have something that can go faster than light because the thing is an object going faster than light will give off radiation it's like a sonic boom if you're if you're going faster than the speed of sound you give off a sonic boom the same thing will happen if you're going faster than light you will have like a visual boom the thing is something going faster than light will lose energy and then as
it loses energy it'll go faster so to give off more energy and and so you get this like infinite loop of massive amounts of radiation being given off by any object going faster than the speed of light and so this would cause all kinds of problems and strongly suggests that that an object going faster than the speed of light is impossible if you could send signals going faster than the speed of light then you could send information going back in time you could use a device that sends information faster than light to construct and I
love this name an object going faster than the speed of light is called the Tachyon tacky meaning Greek for fast you could use that to construct something called a tachyonic anti telephone and the tachyonic telephone lets you call yourself in the past so that's a lets you send signals into the past yeah so it's tantamount to going back in time you can send information back in time like Marty McFly you could send betting results back in time and and then you could become super wealthy and then you'd be you know Biff Tannen then the crucial
thing is we can't go faster than X we can't go back in time that way you can have a thing that the depending on how you define thing you could have something go faster than light if you had a really powerful flashlight or like a laser or something like that and you shown it as something like the moon and it were somehow bright enough to really light up the moon and you were foolish enough to put your hand in front of that powerful laser to make Shadow Puppets then you know with a flick of your
wrist you could send those Shadow Puppets speeding across the surface of the Moon faster than the speed of light those shadow puppets aren't really things you can't use them to send information from one side of the moon to the other you could use them to send information from Earth but that's gonna travel at the speed of light and it's not it doesn't have mass it's not really a thing very disappointing if we can't go faster than light what's the limit well theoretically there's no reason why you can't go as close as you like to the
speed of light I mean you don't want to accelerate too fast right because that'll hurt putting that aside there's no theoretical limit on how close you can get to the speed of light you know you'll have to deal with some nasty radiation and stuff like that but you could get there and actually going back to Star Trek the cool thing is that if you can get up for real close to the speed of light then you could travel anywhere you want the universe within one human lifetime if you go real fast because of this time
dilation effect that happens when you get close to the speed of light it's just that when you come home billions of years will have passed for everyone who wasn't on your ship you [Music]
