Is Time Travel Possible? - The Science of Time With Neil deGrasse Tyson

time travel is a widely recognized concept in   philosophy and science fiction  but is it possible in real life what does physics tell us about time travel is  it possible to travel to the past or the future   neil degrasse tyson explains the nature of time  and the conundrums of time travel in some ways   we're traveling in time now we just happen to be  prisoners of the present in the eternal transition   from the past to the future if you travel fast  enough you can actually leap forwards in time   relativity specifies that you travel  a good fraction of the speed of light   time will tick more slowly for you than all your  loved ones back on earth if your journey is too   long you might be gone for 10 years and everyone  else on earth ages 100 so you've effectively gone   into the future and then everyone you knew when  you left earth is now dead if you want to go into   the past that's a little more problematical  there are people who have recognized what   severely distorted space does the effect that  severely distorted fabric of space and time   they study what effect that has on the passage of  time and it turns out there is a path you can take   around two moving black holes that haven't quite  collided yet where you can end up in the past   of when you started that journey backwards time  travel according to calculations from einstein's   general relativity is enabled by this  severely distorted fabric of space and time   such as what you would get with black  holes that came in their own proximity there are some physical theories that can help  us learn what time travel is and how it works   in 1905 albert einstein published the  first part of his relativity theory   known as special relativity the theory of special  relativity show that particles of light photons   travel through a vacuum at a constant pace of  approximately 300 000 kilometers per second   a speed that's immensely difficult to achieve  and impossible to surpass in that environment   yet all across space from black holes to our  near-earth environment particles are in fact   being accelerated to incredible speeds some even  reaching 99.9 percent the speed of light [Music] he then published another paper in 1915 known as  general relativity these theories are among the   most important theories in all of physics under  einstein's theory of general relativity gravity   curves space and time causing the passage of  time to slow down in einstein's theory of special   relativity time slows down or speeds up depending  on how fast you move relative to something else so   for an observer in an inertial frame of reference  a clock that is moving relative to them will be   measured to tick slower than a clock that is  at rest in their frame of reference this case   is sometimes called special relativistic time  dilation time dilation may also be regarded in   limited sense as time travel into the future the  faster the relative velocity the greater the time   dilation between one another with the rate of time  reaching zero as one approaches the speed of light   scientists have done some experiments to show that  this is true for example there was an experiment   that used two clocks set at the exact same time  one clock stayed on earth while another flew in   an airplane going in the same direction earth  rotates after the airplane flew around the world   scientists compared the two clocks the clock  on the fast-moving airplane was slightly behind   the clock on the ground so the clock on the  airplane was travelling slightly slower in time   another famous experiment is the twin paradox   which is according to neil degrasse tyson not a  paradox at all he describes the experiment as a   hypothetical scenario which uses identical twins  to illustrate einstein's theory of relativity   take newton's laws for example he has a law of  motion and law of gravity then we find out wait   a minute and if there's a high gravity source  newton's laws fail if you're moving really fast   faster than a running horse whatever newton might  have experienced in his life his equations begin   to break down do you throw away all of newton no  it works in all the other cases so what's going on   einstein comes up with laws of motion his special  theory of relativity einstein comes up with a new   law of gravity his general theory of relativity do  they replace newton no they draw a bigger circle   around the applicability of newton's laws  newton's laws apply here einstein's laws take over   and even with einstein his equations can't take  us to the center of a black hole the singularity   that's there the singularity at the beginning of  the universe we know now that his theories fail   they blow up on the page so we have a whole  frontier of science the string theorists we got   top people working on this to try to extend  einstein's laws into an even bigger regime   that can then explain everything  that's in our universe not most things   there have been many scientists who have proposed  time travel theories that describe how time travel   might be possible physicist miguel akubieri  proposed a theoretical solution to einstein's   equations which would allow a spacecraft to  achieve apparent faster than night travel   if a configurable energy density field lower  than that of vacuum could be created rather than   exceeding the speed of light within a local  reference frame a spacecraft would traverse   distances by contracting space in front of it and  expanding space behind it resulting in effective   faster than light travel objects cannot accelerate  to the speed of light within normal space time   instead the alcubierre drive shifts space around  an object so that the object would arrive at its   destination more quickly than light would in  normal space without breaking any physical laws   however the proposed mechanism of the alkyberry  drive implies a negative energy density and   therefore requires exotic matter which has  physical properties that would violate known   laws of physics what leads people to think  that traveling back in time cannot occur   in our universe is the grandfather paradox  this is a well-known paradox of time travel   in which inconsistencies emerge through  changing the past the name comes from the   paradoxes description a person travels to the  past and kills their own grandfather before   the conception of their father or mother which  prevents the time traveller's existence [Music]   there are some suggestions  about how to go into the past   but you go on a trajectory a space-time trajectory  that does not intersect back with yourself so you   can't really interfere with your own past and  so that requires huge energy to execute and   well we're still pulling oil out of the ground  so there's no energy we're anywhere close to   acquiring so the the simplest way is to go  forward in time by traveling very fast uh how fast   a lot faster than any piece of hardware we've  ever made until recently most studies on time   travel are based upon classic general relativity  coming up with a quantum version of time travel   requires physicists to figure out the  time evolution equations for density   states in the presence of closed time-like curves  in einstein's theory a closed timeline curve is a   curve in space-time that could be followed back  in time but not forward in 1991 david deutsch   a physicist at the university of oxford came up  with a proposal for the time evolution equations   with special note as to how it resolves  the grandfather paradox and non-determinism   however his resolution to the grandfather paradox  is considered unsatisfactory to some people   because it states the time traveler re-enters  another parallel universe and that the actual   quantum state is a quantum superposition of states  where the time traveler does and does not exist   another principle that was developed by russian  physicist igor novikov in the mid-1980s expresses   one view as to how backward time travel would  be possible without the generation of paradoxes   according to this hypothesis physics in or near  closed time-like curves can only be consistent   with the universal laws of physics and thus  only self-consistent events can occur anything   a time traveler does in the past must have  been part of history all along and the time   traveler could never do anything to prevent  the trip back in time from happening since   this would represent an inconsistency while some  physicists argue whether time travel is possible   theoretical physicist carla revelli thinks that  time is in fact an illusion and our reality is   just a complex network of events into which we  project sequences of past present and future the   whole universe obeys the laws of quantum mechanics  and thermodynamics out of which time emerges more   on that in another video thanks for watching  did you like this video then show your support   by 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Channel: Science Time

Views: 1,038,223

Keywords: Neil Tyson, Is Time Travel Possible?, Neil deGrasse Tyson, Time Travel, Time Dialtion, Neil deGrasse Tyson - Time Travel, Time Travel into the future, universe, Einstein, relativity, general relativity, time travel into the past, science, the science of time, science time

Id: uPSgO9CkSjQ

Length: 10min 7sec (607 seconds)

Published: Sat Jan 16 2021