Is Time Travel Possible In Our Universe? 

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Who else is revisiting this classic in 1943??

Yayyy new Sleep Video Thank you

“Over then” and “over there”. Very good concept. “Separated by time” being the same as “separated by space” is a very good way to look at it. Thanks for the new perspective.

I love the theory that UFO's are use from the future observing history(for them) as I think most people would love to go back in time to witness what it was like so it is not hard to imagine that future humans are simply observing.

My appreciation goes to the entire staff responsible for the outstanding presentations of each video of The History of the Universe.

This blend of crystal-clear information and fictional sidesteps is just the right cocktail for me. I've been enjoying your series, thank you.

The universe is incredibly fascinating and mysterious. I genuinely want to learn as much as possible about it. If gaining unlimited knowledge of the universe were possible, I would do anything to acquire it.

This is by far one of the best presentations of Physics, astronomy and science I've seen on RU-vid, top marks for this, the production vaule and thorough exploration of the subjects provides a terrific window into some of the most complex topics in a digestible way, keep up the great work.

I don't know if anyone has mentioned something similar or not but your videos have been amazing for my mental health. Too often we're caught with the daily responsibilities of life; find ourselves overly immersed in social media and news that we forget how insignificant we truly are. Your videos are a way for me to just step back from the world and realize all our problems are miniscule when compared to the sheer significant size of the universe and all its physics surrounding it.

In almost every other universe, this content has been picked up by a major publisher and the authors are exceptionally well compensated. I think we will merge with that universe soon enough. Bravo!

One of the best videos on youtube. Concise and informative. Please never change this level of production

Wow...what a journey, hard to digest at times but written and told in such a manner that you have not lost my attention for the finest of seconds...bravo!

This is incredible; what a channel. I can't believe this is free, I really wish we had this stuff when I was a child.

3:10 you can invent the time machine and use it to do a bunch of other things, their is no need to rush to your death, you can have a full life before going back in time and saving yourself. or you can go back further in time and stop yourself from going out this night, you have plenty of options.

You cannot go back or forward in time without knowing *where* you will end up in the universe. Every second, we are moving 220 km, relative to the center of the Milky Way Galaxy. Pretty fast, since the distance we move around the sun in our orbit is 30 km/s. Don't forget to factor in where you are on the planet for spin speed on our merry-go-round. But in what direction is our galaxy moving and how fast? With no other stationary objects in the (currently visible) universe to determine the absolute velocity of the Milky Way through the universe, we are left to imagine what that looks like. Also, what other actors are affecting our trajectory or speed? We did choose the Great Cosmic Attractor and cosmic microwave background radiation to help gauge our velocity, but that is still science in its infancy. We have no idea whether the objects we are racing toward are moving against us (salmon upstream) or whether they are moving along with us (turtles in a current), but at a different speed. It certainly would matter if you traveled in time! This is the difficulty of being Earth-bound beings who have great trouble thinking in four dimensions. We think we are static and that time is static. This is simply untrue, as time is the measure of regular movements, not a universal constant. Not yet, anyway. So here is the final conundrum: Unless our tools for time travel, supposing we are able to calculate the coordinates of where we were or where will shall end up, are absolutely accurate, with no margin of error, a transport will mean ending up elsewhere in space, perhaps in an object, or so far from an object that catching up to it is nigh impossible without another inaccurate jump. I certainly wouldn't want to aim for being _on_ a planet, since I may end up in, on, or around it instead.

If you are here because you don't understand the show "dark." Rest assured. You won't be disappointed.

Not only have you guys delivered another incredibly thorough, thought-provoking video but you've also cultivated an amazing community here on RU-vid! Every time I visit the comments section of these videos I'm met with a wave of positivity. Bravo team, I wish you continued success into the future!!

I watched all of your videos, from the very first one. I loved all of them. Appreciate the hard work. One of my favorite channels on RU-vid for sure.

Just incredible, I’ve watched a lot of context creators and you’re production is simply next level. I absolutely love your value add b roll and not some random space images over and over.

I didn't think it was possible to watch a 48 minute informational video and know less than I did before starting it, but you have proven me wrong. Thank you.

What an Excellent Episode. Really appreciate the effort that goes into the making of such high quality videos.

A new episode of HotU has actually become a major event in my life. I turn off the tools in my studio, put on the big screen to RU-vid and stand there at my work table- transfixed by the astounding script, amazing narration by David Kelly and the superb music and graphics. And all with a DND sign on my door. This would be the first of many, many replays of the episode. (BTW: I particularly love the white-ring, time machine design. It's beautiful!)😮

As someone who is trying to come up with a sci-fi story, I really appreciate the way in which you lay out these large concepts in a way laypeople can understand. It's helpful for someone like me who likes when sci-fi builds off real scientific theories.

thank u so much im currently going insane because of school work and nothing has helped me concentrate more than ur vids i feel so smart

This is one of the most comprehensive explanations on this topic that I have ever had the pleasure of listening to...Well done.

Fun fact: back when the seemingly ftl neutrino stuff was happening, the Italian minister for instruction (Mariastella Gelmini) made a statement where she implied the existence of a tunnel underneath the Alps for the neutrinos to travel through

Amazing video. Only a few parts I had to rewind to try to wrap my brain around again, but overall this is incredibly well-presented, digestable and fascinating.

I listen to these videos before bed or at work and each and every time my mind is blown away.

I can't believe how content this good is simply from a RU-vid channel and not on Netflix.

This channel one of the best on the whole of the internet. Neither Curiosity Stream, nor Nebula channels, nor other RU-vid Channels, nor Netflix, nor AZ Prime, Disney, Hulu, (I've forgotten others),... they dont hold a candle to this. imho afaik As soon as I see you've made a new vid I hop on the bed or couch and get comfy excited af! I wish I had friends that get as amped about things like this. :( It would be nice. This type of joy is meant to be shared. iykwim ♡Thanks so much for your energy and excellence♡

Great work man. You did an all around recap of all the ideas of time travel. I love travel. I love you for your work. Well done!

bro this was a journey and i loved it. keep up the good work!

This was a fantastic presentation, explaining so much and covering paradoxes. Awesome! :)

Love this documentary! I have been thinking about these “Time” ideas for years but the way you have presented it is so fundamentally necessary for enthusiast to comprehend! Absolutely awesome!

I ran across a scenario that supports the Many Worlds concept. The idea originates in the classic computer game MYST. In the Myst Universe the Traveller encounters an island dominated by what appear to be puzzles. The puzzles involve mysterious books when used properly transport the Traveller to Worlds with unusual characteristics. It seems the civilization that created the books used special techniques, materials and language writing the books. Using the book correctly sends the user to a world that exists exactly as described in the special language. My theory of the operation of the world books works because the Many Worlds concept implies a Quantum Universe with an infinite number of possible world lines. The Myst world book describes a world in one of the possibles world lines and using the book correctly transports the user. Of course the user must possess a originating book to return.

Very impressed with this video. I have always been interested in astronomy and physics. It was things like this that drove me to enter those professions. Thank you for feeding my insatiable curiosity about the universe and the wonders that we discove

Your videos quite literally changed my life and gave me a new appreciation of cosmology that I never knew I had inside of me. Thank you so much! On a somewhat unrelated note, I sometimes venture into the recent comments on your videos and am always suprised by the amount of deranged nonsense and negative comments. Even by RU-vid standards, it seems like videos on these subjects attract a lot of people who are maybe a little too confident about their understanding of the universe. I think I’ve made a similar comment before, but I really hope you don’t pay much mind to them. I promise they’re a tiny minority compared to the overwhelming amount of people out there that have endless amounts of appreciation for your videos. I would bet that a good portion of people who benefit from these types of videos just opt to appreciate them silently. Don’t let it discourage you. Thank you so much for everything you do

Yet another amazing episode, thank you for the continued production of this unparalleled content! 👍👍

This is an exceptional video full of information. Usually these types of videos put 5 minutes of information into a 30 minute presentation with a lot of fluff and repeat. Not this one. Well done.

Dude I can’t stop watching your stuff. I watch one then scroll down and see a bunch of other stuff from you and get curious and end up watching like 100 videos!

When I was around 16 (am 51 now), 'Time Life' released a series of books (I still have my set), called 'Mysteries of the Universe' (? If my memory is correct), and there was one about time... I remember reading it and there was one specific weird way of travelling through time and it involved a HUGE MASSIVE cigar shaped man made object set in space. Now, at the time I wasn't fully aware of Einsteins work in modicum detail perse (or a lot of other physicians and their work in this field etc), but, I was really into space, and the science and understandings of behind the Universe etc, and wanted to know more.. And I did consider myself to have a 'Logical' balanced mind. So, when reading about this object (it was required to be many Kilometres in length and the diameter was also something like a Kilometre or more too), the book stated that theories had it that it would have to spin along it's length (ie like a rolling cigar along a table and not 'Spinning a pen' etc) and that spin would have to be a good percentage of 'C' (Speed of light), and then, you say, as a pilot in a ship, would have to approach this big long tube, and then fly your ship at, again, a good percentage of 'C' and fly it in a direction either 'With the roll' or 'Against the roll' of the Huge bulky tube. Now, they said, the theory was, going 'With' the direction of roll of the tube 'Could' send you forward in time, and flying your ship in a roll 'Against' the spin of the huge tube could take you back in time, but... They DID say, that naturally, it would ONLY bring you back to the point of time where the 'Space cigar' had FIRST reached it's required rate of spin and no earlier. Yeah, I got that, seemed logical. And for years it still puzzled me. That is until I started learning more about how your rate of speed is affected by and/or affects the rate of time within Space/Time physics... Still an interesting thing to read though, and those books were/are a pretty damn good read (each book covered everything - ghosts, Nazca lines, Bermuda Triangle, many subjects)... 🤔🤔🤔😏 Edit: (Just watched the rest of the video and...) 31:27 - AHA! There it is! the idea about a cylinder! Nice! 🤔😉 😎🇬🇧

I have two facts to share: 1. It's amazing - and we should all be grateful - that these videos are available to watch here on RU-vid at absolutely no cost to us. 2. It's terribly unfortunate that every single one of these videos has not been made into a documentary and added to the catalogs of streaming services such as Netflix, Amazon Prime Video, and Hulu.

These type of videos help me sleep lol. Not that it's boring or anything but the voice and images are really calming plus you can learn new things .

These videos are so interesting, it's honestly as captivating as a movie like Interstellar but educational its strange and perfectly done great job!

Just a small aside, but thank you for recommending Memories of my Mother. I'm not sure what about it resonated with me so heavily, but I was sobbing by the end of it. Its a beautiful story, rarely have I seen such a short story carry such a powerful emotional weight.

What a beautiful presentation. This is just some of the best quality content available anywhere!

I've been looking for a good time travel vid on RU-vid for a minute, and this is SOLID!!!

Thank you for this video lesson! People who have the gift of bringing difficult subjects to everyone in a simple to understand way are so incredible!

This is some great work. Narrative and actual theory woven together masterfully. Brillinat work. So engaging. So thorough.

finally !!! can’t wait to witness another masterpiece 💯

I've only watched the introduction but it already got me thinking. A possible explanation to where the idea of a time machine was created on this loop is that the future exists in a superposition (similar to the one in quantum theory) where all the possible outcomes exists. And they collapse everytime. So the probability of you thinking of a time machine in the future exists at the same time that you dead also exists in the future. But the moment that the possibility of a time machine is created, one of those futures collapse and you time travel and save yourself creating a loop. If you so choose to not save yourself, then the future becomes you not saving yourself, the time machine not being created and you stay in the past, because you were never saved by yourself essentially you re-visit this moment in time, making it collapse in a new future. As to what happens to you: information cannot be destroyed so you'd keep yourself and your memories and your existence, as if you were transported from another universe, and die of old age. However not creating a time machine. This theory also makes the act of traveling to the future chaotic because you could travel to innumerable different futures as everytime you travel to the future you collapse the superposition into one of the possible futures, and then you could go back in time and pass the information you got in the future to bring yourself to that future, however if someone else traveled after you, they could completely change the future

Imagine you were drinking a glass of water and then you came back from the kitchen to see a piece of paper that says; "This empty glass is what time you have left, enjoy it while you still can... me." *Now, I would be playing games all night just because I saw this.*

Such complicated concepts are explained so beautifully that it makes a wonderful watch… already watch it 3 times in a row and I will rewatch it again many more times ❤❤❤

The way this podcast tells the story that I've heard time after time keeps me wanting more n more...plz keep up ur work

This is the most pleasantly mind melting video you guys have made so far! I finally got time to sit down and rewatch and ponder it today, I learned so much just from this video alone!

I look forward to new videos from you guys so much. Truly a treat, thank you. And man spacetime is weird.

Thank you for the great quality of production. I always enjoy your videos. I watch they from 2 to 3 times to get all the information.

Watched this at 3 am and it was great, although i have to stand up at 6 in the morning i have no regrets. Great video!

I turned 32 yesterday, Ive learnt a new word from this video, ANYWHEN, never knew there's such a word for 31years

Imagine waking one Sunday morning to find this video seemingly magically risen from spacetime into one's RU-vid feed. One could imagine a world where holidays were based upon real magic: the wonders of scientific discovery.

In the infinite void of obscurity we call a universe, it is comforting to have a grasp (granted a very lose grasp) of what is happening. Dope video keep up that amazing work.

It's funny. I use this to put myself to sleep but the next day or the other I finish it. Not just "sleep material" but also excellent info and well structured.

This is my number one favorite YT series

Amazing work as always my friend. Thank you for yet another hour of my life that I've spent deep in thought trying to wrap my head around the idea of quantum physics and time travel. It's always a wonderful time especially when a video of yours is playing simultaneously

The writing is fantastic. Kudos Colin Stuart!

29:20 - 33:00 I do read news articles about traveling back to the past and this was the best explanation about the limits of time travel and how that cylinder would work

Creators of this series are LEGENDS!! Take a bow! Thank you 🙏

When a new History of the Universe videos pops up, I make sure to block some quiet time on an evening asap, disable all external sources of distraction, and enjoy the deep dive into a captivating and masterfuly presented content, undisturbed. Again, you didn't fail to deliver beyond expectations. Kuddos to this channel, by far my favorite out there.

Your videos always amaze me, keep up the great work. This channel is one of a kind

Absolutely fascinating!

This is amazingly done and very informative and interestingly entertaining, GG :)

Well done, as usual. Hand's down, the best science content being produced on this platform.

Everytime I watch this I cry. It has been always my favourite channel. Possibilities are endless. This just confirms how perfect is the balance in this Universe.

What a beautiful ending, accompanied by the sweet, mysterious and ever-wondering feeling enabled by the melodious piano piece.

24:30 minor correction: even though in the movie one of the characters says that the time dilation is due to gravity, in reality the mathematical model they used to animate the black hole and calculate the effects of time dilation was actually time dilation due to relative velocity, not gravity. This is because the black hole was spinning. It’s actually really impressive the math they did to get all of that to work.

Not sure if this will come up in the video but my favorite time travel theory is the reason we don't have any visitors yet is we have to create the a time machine first, like how you have to have two telephones to actually use them. And it's sort of dystopian as when we turn on the first time machine we'll get flooded by everyone from the future looking to go back as far as possible

This might be my all time favorite channel. Every time a new video is posted, I get excited in a way that I can only describe as childlike... From presentation to accuracy to storytelling, this channel pretty much does it all, and does it all about as good as it can be done... But it's the way physics and cosmology are presented in a narrative way that really separates this channel from its contemporaries. If I could sub twice, I would... Thanks for the outstanding content, your time amd effort does not go unnoticed or unappreciated. Bravo.

This video singlehanded helped me to get and understand Dark a little better 😭😭 even if I already finished the series

Most of paradoxes in the beggining is easy to solve. Time-loop not necessary should begins in the same way as the loop cycle starts. You just get into car crash when was young, not died but get disabled for a life, then in many years you learn physics and create time machine/accidentaly get acces to time machine/time machines become usual thing in the future, letter to yourself is may be inside joke from work/literally whatever, you decided to come back in time and prevent car crash and change your disability, but all goes wrong and when you saved younger yourself, you died in car crash and started the time loop cycle for the first time. And by the time when letter become just unreadable, time-loop whill changes and not necessary will stay time-loop at all. Time can be changed with time travels.

Yay, new video. I cannot stop watching these. Been through the entire series like 5 times now. I fall asleep to these trying to soak everything in. So much effort, time and love going into each video , the creator for this series is an absolute genius in content story telling

Thank you for the many excellent videos. Very well thought through and narrated.

I love how it constantly opens up amazing ideas . Than seems to quash them , and than u hear “but there may be another way .. over and over lol

I had a whole story written down on why paradoxes cannot exist, but the video covers that too. One thing I must add, is that time travel alone presents no way to return to a previous time stream. An observer would never hear from you again.

I wrote a short story back in highschool that had time travel in it. I took the approach back then that "You know what? The universe probably wouldn't care that much if we traveled through time." I put together an imaginary model where "every moment in time is traveling through time at one second per second", not understanding relativity back then, but the idea wouldn't need much tweaking to be consistent. So my main character built a time machine, went back in time, made a big change, then traveled back to his time and... nothing changed! He ended up figuring out that in order for the change to make a difference to the time he knows he would need to wait the hundreds of years he went back before the changes would affect the century he exists in. This system for time travel fixes paradoxes, but it might lead to anticlimactic storytelling.

Though I have heard these principles suggested before, your demonstrations of their potential validatity and sucient explain of their workings is top tier. I find it hopefully and motivating that regardless of the adversities I may face in this timeline, somewhere out there somewhen, out there, exists of me who is successful and ultimately will achieve all I can ever have desired. Morbid when you stop to consider the implications of it all but still reassuring none the less.

so many mental gymnastics in the last part, its interesting that travel into the future has been done and is possible but the past is complicated, even though the past is much more real then the future because it is documented and in our memory

I'm traveling forward in time right now. Can't stop.

Every new HotU video is like a little holiday for me. When I see it come up in my feed, I am very excited for when I am finally able to pour myself a drink, dim the lights and forget about everything else for a little while I ponder some of the largest and most difficult questions of our universe through the amazing narration and crystal clear script. It really is amazing what you all are doing, the content is truly next level.

Thank you for all the effort put into these masterpiece videos. Un-ironically doing more to spread physics education and discussion to the general public than most public educational institutions. (Physics department at my college was on probation the entire time I was there- 3 and a half years) Thank you again

The Time Police would never allow it.

I always imagined those sudden stinging pains out if nowhere everyone experiences are those cosmic rays physicists call the Oh My God Particles. Interesting and fantastic!

The many-worlds interpretation is really interesting, but honestly I feel there's something missing because it's too convenient to solve these paradoxes, but since I'm not an expert, I can't say anything further.

I also wanted to add that your video about whether we have found The Theory of Everything is one of the best and most informative videos on the subject I have ever seen. Your explanation of physicist Juan Maldacena's discoveries might be one of the best on RU-vid, if not the best. I would love to see more videos that go that deep and explain Concepts which are that profound. Sadly there is too much content on RU-vid about things which have been explained over and over and over again. You make such wonderful videos than I would really enjoy seeing ones on the new Concepts and theories that physics is currently addressing.

Maybe some future great mind will be influenced by all this information, someone who will unravel more of this weird existence of ours. The video is a great support for all the ideas presented here! Thank you!

I'm not a physicist, I just like watching science videos from time to time. The way I see it, the Theory of Relativity proves that the past exists just like we exist at this moment. It also proves that we exist beyond the 3rd dimension. In the twin astronaut brothers anecdote, they moved through time at different rates, yet from both brothers' perspective, the other brother didn't fade away to a different slice of time. They still exist, which means their beings stretch through time at least from the moment they're born until their deaths, Weird to think about it because we can only perceive our present moment and remember the past, but in reality we are like a film tape stretching from beginning to end, and a potential being with enough perception could look at us and see every part of that range, toddler, teenager, adult, senile, all laid out in front of them.

I appreciate your content! U cover a vast miriad of topics on your channel about different sciences. Not only are they entertaining, your charisma and the calm to your voice make them a must catch! I truly appreciate the fact that your videos r in depth , detailed, contain broken down concepts and lengthy in a sense that truly keeps me captivated! Bless u and i hope your channel grows enough to attract people who truly value this kind of info. Still beats me that all this is free. More growth to you!!!

I remember the first time I encountered the bootstrap paradox, before knowing what it was called. It makes intuitive sense to me, despite being hard to explain. I think this is because what I know of physics leads me to believe there is only one timeline, no splitting off into variable timelines or such. Just the one. Anyways, this encounter with the bootstrap paradox happened in the early '90s from a cartoon show called Gargoyles. The main antagonist, a wealthy eccentric who loves the occult, literally went back in time to save these ancient coins for his future self to sell, starting his financial empire.

Can't wait to rewatch this tonight when I'm ready to go to sleep

One person explained a possible phenomenon of autoinfanticide, which could explain what occurs to your future self should your past self die. I do not recall where exactly I heard this theory from anymore, sadly. When your past self dies, your future self would near instantly regress in age, decompose, and deconstruct, simultaneously. The time machine you arrived in also remains, but returns to the sun of it's parts that existed at the time of your past self, and also goes into a state of disrepair, decomposition, and/or general age, depending on what made up the machine. The likely explanation for this is that your future self is still your future self, bit due to having died in the past, your body becomes the state it would be in within your future after you'd died, making it so that, if you traveled back 50 years, and your body was properly preserved and buried, you'd be drained of moisture, become limp, and collapse, while also having that moment of release before death a second time, since any food you had inside of your body would also need to be expelled, just like your past body would do as it died. The main difference is that food you'd consumed would also return to us former state. Had you eaten a burger, it may become raw veal, or even possibly the productive base elements that cause a cow to be conceived. Any bread would become wheat, or seeds and water. Any lettuce would become seeds, any tomatoes, any pickles. Anything like ketchup or mayonnaise or mustard would become tomato seeds, cow milk, chicken eggs, mustard seeds, various food dyes, etc.