Neil deGrasse Tyson - Can We Go Back in Time Using a SpaceTime Machine?

one of the most intriguing questions we've  all wondered about when we were kids is   whether we can travel into the future or go  back in time using some sort of time machine   Still Remains intriguing Even in our adult lives  and fortunately for us science has advanced to the   point where we can answer this Age old question we  can easily travel forward in time and we've known   how to do that since 1905. Einstein's special  theory of relativity lays out the whole recipe   of how you can move into the future and all you  have to do is go into sort of a lower gravity   field relative to other people or just travel  very fast and your clock will tick slower than   that of everybody else that you've left behind  then when you return you'll be younger than your   twin for example if you had left your twin back on  Earth so in that sense you are traveling into the   future that's easy to do and we've known how to  do that traveling backwards that's the problem we   think we can do that I have some colleagues who've  made some calculations that assert that depending   on a trajectory you take around a black hole you  can come out and end up in the past of when you   started but that takes extraordinary setup to  make happen but right now no problem traveling   into the future we've known the answer that it is  absolutely possible to travel forwards in time in   fact we have irrefutable evidence to show that  so before we dwell into the intricacies of going   back in time first let's see why scientists  are so confident we can travel into the future   the faster you move the slower time ticks for you  as others view it relative to The Observer you   don't know anything's happening your clock still  ticks as far you've still got your your heart   beat all of this so this is not a physiological  thing it is an actual property of the fabric of   space and time under those conditions so I watch  you fly by and the faster you go the slower time   ticks for you so not only does speed do this  also the strength of a gravitational field   will have the same effect on you initially when  formulated you're thinking it's just because   you're moving it's actually way deeper than that  the GPS satellites orbit higher than our space   station the geosynchronous satellites are like  middle orbit that is far enough away from Earth's   source of gravity for them to have a difference a  measurably different space-time condition so that   their clocks tick faster than our clocks on Earth  surface because they're farther away their time   takes faster relative to us but we get precise  timings from geosynchronous satellites how does   this work we pre-correct the time signal from  the GPS satellites to compensate for Einstein's   general theory of relativity so that by the time  the time reaches us it's been properly corrected   and it matters to us and our space-time Continuum  not the one that's in Middle Earth orbit what once   you calculate that then you do and you say oh  my gosh the formula Works Einstein was right   it is true [Music] in physics and relativity  time dilation is the difference in the elapsed   time as measured by two clocks is either due to a  relative velocity between them or to a difference   in gravitational potential between their locations  for example near the vicinity of a black hole to a   distant Observer clocks near a black hole would  appear to tick more slowly than those farther   away from the black hole due to this effect  known as gravitational time dilation an object   falling into a black hole appears to slow as it  approaches The Event Horizon taking an infinite   amount of time to reach it as we said besides  the difference in gravitational potential there   is another way to travel into the future and that  is going through space in relativistic velocities   as you approach the speed of light something  really strange starts to happen let's keep going   faster and faster ninety percent the speed of  light 99 the speed of light time is ticking slower   and slower and slower for you you will watch the  whole future history of the universe unfold in   front of your eyes as fractions of a second go by  for you as you go 99 99.9 99.99 the speed of light   there's a formula for this of course special  and general relativity suggests that suitable   geometries with space-time or specific types of  motion in space might allow time travel not only   into the future but also into the past however  time traveled into the past is theoretically   possible in certain general relativity space-time  geometries only when traveling faster than the   speed of light is permitted and the problem with  going back in time is forgetting about the other   side of the coin of the space-time Continuum which  is space it's not good enough just to travel back   in time you need something to propel you in space  as well so it's a space time a space-time machine   not just a time machine because Earth is a moving  Target I just want to make that clear and by the   way just to go back in time you could still  land on Earth but how was Earth rotated you   can end up in Siberia in the middle of the ocean  probably because most of Earth's longitude is   spanned by ocean so it's truth in time travel  with regard to these space-time coordinates now   we call these your coordinate in space and your  coordinate of time we call that your world line   another problem with going back in time using  a time machine or a space-time machine is the   so-called grandfather Paradox but what is it  exactly you cannot go back in time and prevent   your parents from meeting each other because  then you would have never been born to have   gone back in time to have prevented your parents  from meeting each other this is the fundamental   Paradox of time travel and so if there were a  rule book that'd be number one rule perhaps the   best way to go back in time is to make use of  wormholes the theory of general relativity does   suggest a scientific basis for the possibility of  backward time travel in certain unusual scenarios   so going through a traversable wormhole could in  theory allow you to go back in time so we have the   sort of the fabric of the space-time Continuum  it's not just that space is out there space is   intricately configured with time and how do you  know this space time are forever conjoined this   fabric can be distorted in such a way that you  can change the distance the space-time distance   between two locations and one way to imagine that  is imagine all of our universe is just on a flat   sheet of paper you're on one edge of the paper  and I want to get to the other Edge and I'll   take out light years of time whatever however  long that takes it's light years distance so   I take many years traveling at the speed of light  but if I take the space and warp it curve it back   on itself now your location is very close to me  if I could somehow punch through the fabric of   space and time and reach your location something  that would otherwise be longer a shorter distance   and thereby transcending the speed of light to do  so you're no longer limited by the speed of light   the diameter of our galaxy is a hundred thousand  light years you can't travel across it unless you   figure out a way to warp space and time so in  that warp in principle on paper you can have a   hole that you pass through and just come out the  other side and you're in another place and if you   did it right you can show up at another time and  that's the most classical invocation of a wormhole   another approach for backwards time travel  involves a dense spinning cylinder usually   referred to as a tipler cylinder discovered as a  solution in general relativity this hypothetical   cylinder is infinitely long and Spins fast enough  about its long axis and a spaceship flowing around   the cylinder or a spiral path could travel back in  time or forward depending on the direction of the   Spiral however the density and speed required  is so great the ordinary matter is not strong   enough to construct it by the way if you manage  to travel someplace faster than light you have   the capacity to move backwards in time we've  got that one established as well we just don't   have any easy way to travel faster than light but  one way that's been celebrated in science fiction   and you can write it out on paper legitimately  is a wormhole a wormhole I'm over here and I   want to get over there and I want to get there  quickly you can travel through a wormhole that   changes the effective distance between where you  are and where you're going and then you sort of   look around when you get there and you find oh  my gosh I've traveled a hundred thousand light   years in a matter of a moment when you do that  you have the capacity to move backwards in time   relative to when you left now you don't get to  visit yourself you're in a sort of a different   space-time trajectory so you can't shake hands  with yourself before you left and by the way   there's a huge Paradox that people worry about  and many people including Stephen Hawking the   late Stephen Hawking worried whether this Paradox  would prevent backwards time travel completely   because if you go back in time and prevent  your parents from meeting one another then they   wouldn't have ever given birth to you to go back  in time to prevent them from meeting one another thanks for watching did you like  this video then show your support   by subscribing ringing the bell and enabling  notifications to never miss videos like this thank you

Channel: Science Time

Views: 626,204

Keywords: neil degrasse tyson, neil degrasse tyson time travel, neil tyson back in time, neil degrasse tyson can we go back in time using a spacetime machine, neil tyson time machine, travel into the future, grand father paradox, physics, space, time, spacetime, einstein, relativity, black hole, astrophysics, quantum physics, can we travel into the future, time dilation, time slows down, backwards time travel, can you go back ine time, science, science time

Id: yI9IL9pNcpg

Length: 10min 2sec (602 seconds)

Published: Sat Dec 10 2022