How Far Can You Travel? Voyaging Billions of Light Years in a Human Lifetime

If you accelerate at 1G, you can create artificial gravity inside your spaceship. And there’s the added advantage that you can cross billions of light years within a human lifetime. How far can we travel?
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Team: Fraser Cain - @fcain
Jason Harmer - @jasoncharmer
Chad Weber - [e-mail]
Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down - “X-Ray”
• Left Spine Down - Side...
In a previous episode of the Guide to Space, I talked about how you can generate artificial gravity by accelerating at 9.8 meters per second squared. Do that and you pretty much hit the speed of light, then you decelerate at 1G and you’ve completed an epic journey while enjoying comfortable gravity on board at the same time. It’s a total win win.
What I didn’t mention how this acceleration messes up time for you and people who aren’t traveling with you. Here’s the good news. If you accelerate at that pace for years, you can travel across billions of light years within a human lifetime.
Here’s the bad news, while you might experience a few decades of travel, the rest of the Universe will experience billions of years. The Sun you left will have died out billions of years ago when you arrive at your destination.
Welcome to the mind bending implications of constantly accelerating relativistic spaceflight.
With many things in physics, we owe our understanding of relativistic travel to Einstein. Say it with me, “thanks Einstein.”
It works like this. The speed of light is always constant, no matter how fast you’re going. If I’m standing still and shine a flashlight, I see light speed away from me at 300,000 km/s. And if you’re traveling at 99% the speed of light and shine a flashlight, you’ll see light moving away at 300,000 km/s.
But from my perspective, standing still, you look as if you’re moving incredibly slowly. And from your nearly light-speed perspective, I also appear to be moving incredibly slowly - it’s all relative. Whatever it takes to make sure that light is always moving at, well, the speed of light.
This is time dilation, and you’re actually experiencing it all the time, when you drive in cars or fly in an airplane. The amount of time that elapses for you is different for other people depending on your velocity. That amount is so minute that you’ll never notice it, but if you’re traveling at close to the speed of light, the differences add up pretty quickly.
But it gets even more interesting than this. If you could somehow build a rocket capable of accelerating at 9.8 meters/second squared, and just went faster and faster, you’d hit the speed of light in about a year or so, but from your perspective, you could just keep on accelerating. And the longer you accelerate, the further you get, and the more time that the rest of the Universe experiences.
The really strange consequence, though, is that from your perspective, thanks to relativity, flight times are compressed.
I’m using the relativistic star ship calculator at convertalot.com . You should give it a try too.
For starters, let’s fly to the nearest star, 4.3 light-years away. I accelerate halfway at a nice comfortable 1G, then turn around and decelerate at 1G. It only felt like 3.5 years for me, but back on Earth, everyone experienced almost 6 years. At the fastest point, I was going about 95% the speed of light.
Let’s scale this up and travel to the center of the Milky Way, located about 28,000 light-years away. From my perspective, only 20 years have passed by. But back on Earth, 28,000 years have gone by. At the fastest point, I was going 99.9999998 the speed of light.
Let’s go further, how about to the Andromeda Galaxy, located 2.5 million light-years away. The trip only takes me 33 years to accelerate and decelerate, while Earth experienced 2.5 million years. See how this works?
I promised I’d blow your mind, and here it is. If you wanted to travel at a constant 1G acceleration and then deceleration to the very edge of the observable Universe. That’s a distance of 13.8 billion light-years away; you would only experience a total of 45 years. Of course, once you got there, you’d have a very different observable Universe, and billions of years of expansion and dark energy would have pushed the galaxies much further away from you.
Some galaxies will have fallen over the cosmic horizon, where no amount of time would ever let you reach them.

[@MarinOS2107]

thanks einstein

[@The_NSeven]

same

[@Lonesomepoet]

Marin No problem.

[@regaladogerome1749]

Your welcome

[@ZeroHiking]

Danke

[@blanchbacker]

Really appreciate the hard work you put into these videos! You deserve way more subscribers. This blew my mind

[@frasercain]

+blanchbacker Thanks! Share it with your friends.

[@a64738]

I have always wondered why everyone keeps forgetting that we do not need to travel faster then light to even travel between galaxies in a lifetime when accelerating at 1G...

[@whatthefunction9140]

1:59 "this amount is so minute that you'll probably never notice it." ..... so you're telling me there's a change.

[@evilcam]

Great vid. I think more people need to know about this effect, as when you learn this, you basically have to stop making the mistake of thinking there is a preferred initial reference frame in which time moves universally through the Universe. On top of that, when you understand length contraction and other effects, you then have to acknowledge that the nature of space and time really can't be separated, and that time is so intricately a part of space that they are really just parts of the same, unifying thing. I think most of us of course know the words, but I don't know how many really get that. The more who do, the merrier. Oh, and I of course already loved this channel, but that you suggested that excellent Nutshell vid ramped up my respect for the channel, and you Fraser. I love it when some of my favorite youtubers talk about some of my other favorite youtubers, and spread the love around to one another.

[@treefarm3288]

I did learn this in high school physics 50 years ago, and sf author Alistair Reynolds portrays a future where people do get around like this, but very well-explained, Fraser. Thanks.

[@colesnorris]

Always thought provoking, thank you Fraser!

[@DamianReloaded]

I would be willing to experience 1g spot acceleration until I see the stars! XD

[@rushwal]

mind blown...

[@tobi12022]

+rushwal yup 0_O

[@regaladogerome1749]

Ya

[@ananddesh]

Great buddy.. all videos will keep you beyond imagination

[@usernamehyt]

wait a min, does that mean if I am dying from a diseases and I get on the spaceship go to the spaceand travel at close speed of light travel for a few years and come back to earth, by the time I comeback earth already past a few hundred years and have more advance technology to prolong my life.

[@frasercain]

Yes.

[@TiagoTiagoT]

Or maybe you'll come back and find the machines took over and there are no humans left.

[@adolfodef]

If you fly following a spiral path centered on the solar system, you can even get a signal from Earth (from when they discovered a treatment for it) in a reasonable time [your ship will not be moving completely against Earth, so it will take less time to slowdown and came back]; going directly to it. Also, when you finally get to Earth, the treatment will be more refined/tested/better.

[@1buellrider]

Rajesh N 20 years for the space traveller, hundreds of years for earth. Time slows as you approach the speed of light. At the speed of light, time stops completely. Photons that left stars billions of years ago, have not aged at all and are still brand new.

[@rowan9367]

Or you can bring back a deadly disease that was wiped out. not necessarily the same deadly one you have

[@clintwolf4495]

Fantastic video. Thanks.

[@frasercain]

Thanks for watching!

[@liammaher9572]

Quality work Fraser! Loving these videos :) If we travel faster than light (I know it's impossible) would we then travel into the past?

[@Signal_Lost.]

Nope. We would just keep going forward faster and faster.

[@jameskilrain38]

Yes,however this is impossible.

[@HammadWaseem1]

This is a huge time difference. Thanks, man. too interesting.

[@frasercain]

Yeah, time dilation is a mind bending concept.

[@kostasmetal7]

Lol, that were the same examples that i did in my physics lectures in the university :P Awesome videos! Keep them up! ;-)

[@khalidoubelque6140]

Great question , and thank you

[@lladerat]

wait wait wait, so if an alienship lands on my backyard... these guys could in theory be our ancestors, not their kids but THEM leaving Earth thousands of years ago. Cool thing to think about.

[@panagiotiskoronis4861]

No because while you travel, the universe expands as well, faster than the speed of light. The earth would not be in the same position. There is no going back by travelling lightyears.

[@mawage666]

This video was so good, I hit the replay button and watched it twice. On a different subject, I hope if we humans ever come up with a way to go to the moon recreationally and regularly that someone sets up a sweet disc golf course. Obviously the discs wouldn't fly anything the same as they do here on earth, but it would still be fun to play.

[@Caseylawton]

Dude you could absolutely launch a disc on the moon. We'd need range finders just to see our baskets and plan our tosses. Sign me up!

[@mawage666]

@@Caseylawton The discs probably wouldn't go very far as you wouldn't be able to really crank on it with a space suit on, plus there is no air to create lift for glide and stability. But I bet putting would be fun as hell!

[@Caseylawton]

@@mawage666 now I Wana see this guy do another video on the physics of disc travel on the moon! 🤣

[@sashko8922]

1. Does the ship have to have enough fuel for 20 or 28000 years of acceleration at 1G to reach the center of the Milky Way? 2. Wouldn't the ship eventually squeeze so much it could not operate? Say to the Plank dimensions?

[@paulskillman6634]

Really like your cosmo plant behind you.

[@frasercain]

Hah, cosmos are one of my favorite flowers. :-) I like the name too.

[@dff1286]

I love one way time travel, cant get enough of it so I do it every day.

[@shk740]

Sir does the speed of light that emit from all the different stars out their in space are all same? or they are having different speed and velocity...? My Question is Does the speed of light is same throught out the universe or the light emit from one star and from another star have different travel velocity and speed.. plz answer for question

[@buttergurls6401]

so if Every one around me starts moving really slow, I know I'm traveling at the speed of light

[@tccb1833]

Ok I really have to know now. What's the use of that clicker that you're using? Is it to change slides on some monitor that you use to remember what to talk about? Also, isn't the observable universe more like 45 billion ly in radius?

[@frasercain]

+TCCB1833 It's a bluetooth remote control. Yes, the actual observable Universe is 46 billion, but I was saying what it would take to travel 13.8 billon. If you want to go 46 billion, then 46 billion more years of expansion will have happened, so it's kind of a moving target.

[@inglestaemtudo]

Hello Fraser, great video ! Is there any calculation for relativistic space travel at Warp Speed? .... Oh i'm watching too much Star Trek lol.

[@frasercain]

As long as you don't try to go faster than the speed of light, try this one: convertalot.com/relativistic_star_ship_calculator.html

[@inglestaemtudo]

Fraser Cain thx

[@rogermeyersjr]

Hi. Love the channel! I have a few questions so I'll just jump right into it Earthlings would see my clock running slowly and I would see their clocks running slowly, but since I'm the one in an actual accelerated reference frame, that's what breaks the symmetry, right? Such that, in reality, clocks are running faster on Earth than they are on my ship. 1. But free fall is an inertial frame, not standing on the surface of the Earth. Even skydivers spend 99% of their lives in a genuine accelerated frame of reference while on the ground. Given the equivalence principle, why are we not in exactly the same boat as the guy on the 1g spaceship? I understand that there's gravitational time dilation too, but for the guy on the ship, his time dilation is on an exponential curve, no? But our gravitational time dilation on Earth is more or less constant, no? 2. I decide that I want to watch the universe evolve and die over the course of a human lifetime, so I build a 1g ship with a bucket seat, a popcorn machine and a huge window. I think I'm gonna watch trillions of years of superclusters merging, stars living and dying, and black holes evaporating over the course 60 some odd years, popcorn in hand, but I'm gonna be disappointed, won't I? Cuz I won't see off board clocks running faster and faster, I'll see them running slower and slower? But then when I stop accelerating and return to an inertial frame for the first time in 60 years, what do I see out my window? Does everything go really really fast for a nanosecond in order to present me with a universe that's trillions of years older? (Assume that this whole time the window filtered out the blueshifted CMB that would otherwise have cooked me) 3. What if we, humor me here, stop "privileging" inertial frames. Imagine that all of Einstein's life, living right across the street from him there was a boy named Ienstien, again, humor me. Ienstien lived a life identical to Einstein's except for one respect. Ienstien's theory privileged accelerated frames. According to Ienstien's theory, the speed of light is not a speed limit. A ship accelerating at 1g surpasses the speed of light after about a year, no big whoop. What would Ienstien's theory look like? What would the math look like? Would it even regard c as constant?

[@Signal_Lost.]

Wow

[@JCpatriots]

Seriously, space and space travel is absolutely fascinating.

[@PerroV]

Time travel in a nutshell, basically. I don't mind doing 10 years from my perspective but thousands of years from Earth's perspective. Then when I come back in, like, the year 26,493 or whatever, I wanna see what technology has brought us.

[@frasercain]

Yeah, If this was a trip I could take, I think it would be worth it. I'd love to be able to see the far future.

[@goodguytrixx4877]

this BLEW my mind

[@frasercain]

Yeah, it's a pretty amazing concept.

[@vdiitd]

Hi Fraser, what do you think would have happened if the speed of light was much faster, say, for example around a trillion Kms/s? Would there be any change in the way how we perceive the universe?

[@frasercain]

For sure, we'd see much farther out into the Universe, since light would have traveled more distance in the same amount of time. We see Alpha Centauri 4.3 years ago, but with your faster light speed, we'd it how it looks almost now.

[@daniellee6912]

so basically interstellar in real life

[@BHRxRACER]

interstellar is based on real life (advise from physicist by the name of Kip Thorne)

[@thecaptain2281]

Interstellar is very much science FICTION. The producers consulted with scientists about real world physics and how some things "might" work and be perceived. The movie gets a lot of things right, but also takes very serious leaps into fanciful fiction. Black Holes[IE Singularities] are NOT Einstein/Rosen bridges and it is VERY unlikely that they can ever be used in such a fashion. And the multi-dimensional time-space that Cooper[Matthew McConaughey's character] entered into, while seriously clever and interesting, isn't quite right.

[@YashwantMusic]

+Alexander Harvey Fiction isn't supposed to feel right and real. That is why it is called fiction.

[@thecaptain2281]

Yashwant Baskaran "Feel" is an interesting choice of vocabulary. Just because something "feels" right doesn't make it real. In the middle ages people used to "feel" right about conducting a ritual called "trepanning", in which a hole was drilled into a sick persons head and was supposed to release "demons" to save their soul. They also thought the universe revolved around the Earth. And it made sense to them because it's what they saw with their own eyes. Just because something "feels right and real" doesn't actually make it right and real.

[@questioninconnu]

or gunbuster.

[@markbgale]

Reminds me of the plot of Stephen Baxter's Xeelee novels. Set a 20 year return course and tow one end of a wormhole. The other end remains in the solar system. Then you arrive back after many many years have passed and can see the state of Earth, then send information back through the wormhole to old Earth where only 20 years have passed.

[@DagothUrWelcomesYou]

I think about this stuff a lot. It makes my head spin and I get all dizzy x_x

[@frasercain]

This is a particularly mind-bending concept, so don't panic if it's giving you a headache.

[@colinp2238]

No that's alcohol doing that.

[@addydiesel6627]

-The amont of force (F) required to maintain acceleration (G) is proportional to mass of spaceship (m): F=Gm -The work needed (W) is proportional to force and distance (d): W=Fd Since we constantly accelerate or decelerate at G we can use entire distance in calculation -For a tiny 10,000kg spaceship travelling to Alpha Centauri: Work(Joule)=10,000Gx 4.13 x10^16 metres =4.13 x 10^21 Joules. But since 1kg of uranium gives 10^14 joules: We need 4x10^7 kg uranium to pwer the journey. I.e 40,000 tonnes of uranium. Sorry. But it may eventually become feasible with other future technology

[@razeshormaharjan1508]

Even the light takes 20,000 years to reach the center of milky way, then how can you say a spaceship with 99.999999% the speed of light reach the 20,000 light years distance in just 20 years?

[@frasercain]

That's how time dilation works. The rest of the Universe would see you take 20,000 years to make the journey, but you would only experience 20 years.

[@Mogamishu]

@@frasercain all theory. Nobody has done it to actually verify if that is how it would work in practical terms. So you are saying there is no need for FTL warp drive speeds, since as long as someone gets close enough to the speed of light, they can apparently cover vast light-years of distance faster than light? Does not make sense.

[@anthony37860]

Someone Else you’re not traveling faster than light, its just the time dilation makes the trip feel like that. For everyone else watching they will see you take 20000 years

[@unvergebeneid]

I guess the rocket equation is a real bitch for these kinds of spaceships.

[@The_NSeven]

wait wait wait wait wait, this was uploaded on may 23rd and you commented on may 21, how??? O_o

[@NinetooNine]

Maybe you can help me as there is something about this concept that has always confused me. If you are accelerating at 1G constently then you should be traveling faster and faster over time. Wouldn't the acceleration eventually kill you? Especially as you near C.

[@dronekong1634]

I have a Question? I think what he is saying, according to Einstein is right. When you travel fast your time slows down if compare with person moving slow or standing .... interesting. But i have a question keeping the above in mind how can you measure the actual speed of light or you can't?

[@Theodore-mr4el]

somerhing for a new video.Is there a universal ''now''? as i write these lines ,this snapshot of spacetime ,is it common along all universe?

[@frasercain]

We did a video about this here: kzbin.info/www/bejne/gIjRlKqIibJ-oas

[@blakefhs]

Please do an episode on extreme cold in the universe, absolute zero and the possibility/impossibility of going below absolute zero. And could there be a relation to dark energy?

[@frasercain]

We'll do a "coldest place in the Universe" episode. Hint... it's here on Earth, in laboratories.

[@lenerdchirch5038]

after listning to this it makes perfact sence

[@frasercain]

Thanks, I'm glad that worked for you.

[@PhysicsPolice]

2:37 ".. from your perspective ... flight times are compressed." Not quite. It's not the "flight time" per se but the effective distance between stars that is compressed due to length contraction in special relativity. The clocks in your space ship will tick normally "from your perspective". Your flight time will not shortened ("compressed"?) because the distance to your destination, should you be correctly pointed in that direction, will decrease. Indeed, this means space travelers can travel long distances before they grow old and die. Which is what you seem to have been getting at.

[@Mogamishu]

Is an interstellar starship capable of faster-than-light travel something a type II civilization would be able to develop? Or would it require type III civilization technology? I have asked several places and nobody is able to predict when the first interstellar starships will be developed.

[@krissisk4163]

The edge of the observable universe is more than 13.8 billion lightyears away. Remember the space between here and there has stretched quite a lot in the 13.8 billion years since the light started our direction, so it's actually more like 46.5 billion lightyears away now. Actually that concept is mind-bendy enough to make a pretty interesting video. You should tackle it some time.

[@TheACG22]

So if you're already 99.9999999999% the speed of light, how do you maintain 1 G? Wouldn't you eventually just hit c (w/ infinite energy of course)?

[@frasercain]

It's all relative, you can keep accelerating from your perspective. You feel the 1 G acceleration but your absolute speed still doesn't get to c. Time dilation is the consequence. I know, it's totally mind bending.

[@LouSaydus]

No, because your frame of reference never moves, the world moves around you. You are always at the center of your own universe.

[@7777drummer]

is there a link to that other video on getting to the limits of the universe?

[@TheSimonHxC]

+steven kemsley yes, I'll get it to ya, just a second

[@SuperLaugh20]

I always wondered about time dilation, but couldn't wrap my head around how would the universe change as we start to deaccelerate. Sure objects around start to move slower as we accelerate, but as our speed decreases, do objects around start speeding up so much so that it starts looking like its going fast forward? Or would everything fall neatly into as we peacefully deaccelerate at 1G? I'm just stumped at how would the surroundings change for the traveler.

[@frasercain]

+SuperLaugh20 Remember that you're still going super fast in the same direction, even though you're decelerating. You wouldn't see things change until you dropped out of relativistic speeds.

[@SuperLaugh20]

+Fraser Cain Oh how could I have forgotten what Sagan said about the view forward, thanks for clearing that up, keep making amazing videos!

[@GreyFang9]

One question that I do have is this: Doesn't the cosmic horizon reset for the observer? Leaving aside relativity for the moment, If I hyperspaced/quantum jumped/etc. to 14 billion ly from earth instantly, would I not be able to see light information from the my new surrounding at a radius of billions of ly in every direction even-though some would be impossible to see from earth?

[@frasercain]

+GreyFang9 It does, but you'll always be inside a volume visible from Earth, because you're not exceeding the speed of light.

[@GreyFang9]

Hmm? Right... because we can see back almost to the beginning... The missing variable from my question was what would I experience if I did this a few billion years from now when the expansion of space-time has pushed things I would've seen today beyond the cosmic horizon. Could I go see other remnants that I can (and will) no longer see from uh... _"*Milk*-dromeda"_? (ugh...)

[@GCDvlogs]

I have two questions (i think haha): My first is, would a star wars Mellennium Falcon-esk travel be possible? And my second is, could you explain what happens in interstellar when they went down onto the water planet and that took up loads of years back on earth? I'm really struggling to get my head around it :) Anyway, superb videos, i've just watched around 9-10 of them starting with the Terraforming ones and the content really is outstanding!

[@TiagoTiagoT]

So far, we haven't found a way to make faster than light travel possible. There seems to be some promise in the warp-drive area, but there are still some holes we need to fill.

[@GCDvlogs]

oh awesome, thanks for replying :)

[@TiagoTiagoT]

I'm not sure why I didn't answer your second question the first time. From what I understand, what happened with the water planet on Interstellar was that the planet orbit the blackhole close enough that the time dilatation caused by the blackhole's gravity was significant; and they didn't explain it right in the movie, orbiting around the planet would have very similar time dilatation; to have a faster time they would have orbited the blackhole itself at a much larger orbit than the planet's.

[@paulorodrigo2230]

ooi!! você poderia fazer um vídeo sobre as descobertas que fizeram de saturno com a cassini

[@Confederalist]

According to the Kurzgesagt video you referenced it would be impossible to travel outside of the local group no matter how fast you travel. Is that right even if your going 99 percent of C?

[@sarkauz]

If there are forces greater than speed of light , then why do we still measure time dilation considering v^2/C^2 ? Doesn't the scale of relativity change ?

[@-dimar-]

I think that the universe created us humans just to amuse itself.

[@frasercain]

+Dima R Humans are how the Universe perceives itself.

[@-dimar-]

+Fraser Cain Does it mean the universe has some kind of identity disorder?

[@rasfilmon]

Yes the universe created us but who created the universe? "Something out of nothing" contradicts itself; intelligent creator maybe but no strong evidence.

[@01ha]

+HIM Haile Selassie I Rastafari who created the "intelligent creator" in the first place?

[@tonyon2342]

(2b)...interstellar travel (thousands G of constant acceleration)...and maintaining the living areas to 1g with gravitational transformers...to 9800 kms/sec²...Day 508: Half Journey...1 million light years...high hyperluminal-speed = 0.0455 light years/sec...in 2.79 years, here is Andromeda...spherical\tridimensional\spatial Heading...intergalactic navigation in Starships to thousands G of constant acceleration ((typewrite: interstellar travel constant acceleration))

[@xanider5098]

I would make random pit stops here and there. Hopefully meet people. Maybe humans in the future who mastered space travel. (time dilation is no longer a factor) then, when nearing the end of my life, I would accelerate forward till the end of time. watching the universe slowly fade out as I do. Sounds grim but i find it very cool! Calling it quits when the universe does just seems too awesome!

[@frasercain]

Yeah, if you could get going fast enough, you could watch the Universe die.

[@xanider5098]

@@frasercain I asked a few people and they said you would travel around 2x10^33 LYs at 99% the speed of light for 75 years! So fascinating!

[@TiagoTiagoT]

Why motion acceleration has such a different effect on relative time when compared to gravity acceleration? Aren't they supposed to be indistinguishable?

[@xanider5098]

Me as a child: This is BORING! Me now: "SO...FUCKING....COOOOOOOOOL!!!!!!!!!!!!!!!!!!!!" "I wonder if we will be able to do this one day!" "Can human spread across the galaxy?" The Universe?!" "WE CAN EXPLORE THE UNIVERSE! "

[@frasercain]

Hah, same here. :-)

[@KeqingMain278]

The radius of observable universe is 46.6 billion light years.

[@kohZeei]

+NickeTMD really? i thought it was more like 13

[@junjungwapo66]

+LiveToby remember bro, the universe is expanding. So it is true that the universe is 13.8 billion years old, but the universe has expanded to about 93 billion light years in diameter right now. Cheers.

[@kohZeei]

+Angelo Garcia yeah but he said the observable universe

[@junjungwapo66]

+LiveToby yes the observable universe is 93 billion light years in diameter. The observable universe is also expanding, hence what was 13.8 billion light years back then is now 93 billion light years big. Think about it this way, when we look out and see an object 7 light years away, after some time that object is no longer going to be 7 light years away from us. Just like the universe that we saw was 13.8 billion light years away is now 93 billion light years away.

[@junjungwapo66]

+LiveToby hope this helps: en.m.wikipedia.org/wiki/Observable_universe

[@christiancao4718]

If you traveled in a circle. such as around our solar system, near the speed of light, would you essentially travel to the future?

[@bmwolgas]

Fraser - I don't understand how an object's speed can be measured as a percentage of the speed of light when the speed of light is constant, but the speed of matter is relative. Wouldn't that percentage vary depending on your frame of reference? For example, what if in this video, instead of 1 person leaving the Earth and accelerating to 95% the speed of light, what if TWO people left the Earth, each in opposite directions and each at 95% the speed of light relative to the Earth; what is their speed relative to each other? Is it still 95% the speed of light? Or 190%? Or something else?

[@Alexiully]

As some guy said bellow in the comments, we can build up the real VR as in SAO, to explore things and feel them as 'real' based on data collected, but the mind blown part behind it, is another one, what would we define as reality vs virtual world, if we can build up a fully 100% VR dive going bio-digital as in teleportation to that created world, would open an infinite amount of possibilities, we can create real matter out of digital pixels, we would basically become gods, and adds up another question if we can create such a thing, is it maybe possible that all the universe we know before hand was actually made in the same way?

[@younessofri5920]

This is really mind boggling for me. I mean it's more logical to say that travelling at exactly the speed of light, the journey to any place in the universe would take me exactly the same amount of time that takes light. If light reaches the nearest star in 4.3 years, why would going at 95% the speed of light take me 3.5 years and not more?! And thank you for the efforts you're making to produce such great videos! Keep going! ☺

[@Reuben-John]

I think he said it would take you 3.5 years from your point of view, but 6 or 8 years for someone on earths point of view.

[@tomdrowry]

Aren't gravity and acceleration equivalent ? So by sitting on surface of the earth with a constant force of 1 G , 9.8 N why doesn't time in rest of universe slow down relative to us on the Earth,as it does with an accelerating spaceship ?

[@fullmetal1408]

What dilates spacetime is not acceleration, it's speed.

[@TiagoTiagoT]

What slows time near a blackhole?

[@fullmetal1408]

***** Near a blackhole what bends spacetime would be gravity (or directly the mass/energy of the blackhole that is producing such gravity).

[@TiagoTiagoT]

+fullmetal1408 But why the 1g gravity of Earth doesn't dilate time the same as the 1g acceleration of the spacecraft?

[@fullmetal1408]

***** Because time dilation doesn't depend on acceleration, it depends on velocity and gravity.

[@muttleymutt4967]

At 2:02, "That amount is so minute that you'll probably never notice it." Haha, think it's safe to go on and say that you will never notice it.

[@frasercain]

+Muttley Mutt But then someone's going to invent an app that calculates your personal time dilation, and I'm going to be brought up on charges by the pedantocracy. So I dig into my bank of weasel words and cover my ass. Actually, yeah, when I was doing the video I thought that was unnecessary.

[@kturob]

how far do you think humans will ever reach will be Pluto or another star system the way it's going it looks like the moon or Mars might be it for a long time at least our lifetime

[@Snowy123]

Wait... Can you simply it so I can explain this to a girl in a bar while drunk?

[@frasercain]

+SnowToad When you go fast, your travel time decreases from your perspective.

[@Snowy123]

Fraser Cain why?

[@GreyFang9]

+SnowToad Hey, try this (if the _"girl"_ is in her 30's then video tapes would be a better analogy) _"...Life is like watching a Netflix/On Demand" movie that you can only watch once and can never start over. Watching the movie at normal pace means that you and the movie both experience the 2 hours together. Accelerating toward the speed of light would be like hitting fast-forward on the remote. When you do, your time remains normal --1 second per second, the movie and the characters in it now blip by at about _*_5 seconds per every one second that you experience_*_. Hit the fast-forward button again to advance faster, and then it becomes 10 sec to your 1... press it again, then it's 20 to one, and so on... Hold down the button and eventually the entire movie flash by and ends in about a minute."_

[@blobdragon2678]

+SnowToad because the light speed is constant for everyone, but the faster you go, the slower it will be for everyone else ( from your perspective).

[@ajv336]

@@blobdragon2678 yes, but there's still an underlying reason for that: a photon travelling at the speed of light within the confines of your spaceship (say you turn your headlights on) would technically be travelling faster than light from the POV of an observer on Earth, due to the fact that you'd add the velocity of the ship to that of the photon in it. That is not possible, as C is a constant and nothing can travel faster than light (not even the light you generated by switching your headlights on), so the relativistic answer is, quite amazingly, that time gets stretched out to allow for the speed of the photon in your spaceship to remain within the realm of the physically possible. In other words, if the photon from your headlights experienced time the same way as the observer on Earth, it would travel further than 300km in a second. Again, that is not possible. Time experienced by the spaceship and its occupant therefore gets more and more stretched as the speed of the spaceship (from the astronauts' POV) increases, to basically prevent the infringement of the laws of physics that would otherwise take place. When Fraser mentioned that you experience time dilation even when driving a car, that's what he meant: you can't add the speed of the car to the speed of the photons generated by your headlights (from the POV of an observer at the gas station), therefore your time has to pass more slowly. However, being the speed of your car absolutely minute compared to the speed of light, the time dilation will be equally minute

[@thedoctoroa7515]

What about teleportation if I launched 1 pad to the edge of universe and one on earth and teleported to the edge for a second and came back will everything be gone?

[@dotnet97]

Well, depends on how this teleporter works, it'd need a way to send signals to the other pad which would only move at light speed, in which case there's no way you'd be there in a second.

[@matthewftbailey]

If the ship is decelerating for half the journey, why doesn't a 5LY trip take 10 years from the perspective of Earth instead of 5? Would there be a significant difference for a craft accelerating the whole distance vs. decelerating for half?

[@dutchdevil2]

My question is, how does your body age? When you are traveling that fast, Do you age in the same speed as you would do on earth?

[@a64738]

1 year is one year for you but on earth millions of year will pass... So both yes and no.

[@luke_0605]

This is the closet thing to time travel we have so far

[@frasercain]

Yup, time travel into the future.

[@dipak002]

blew my mind away... So one question - if I accelerate at 1 G constantly then in one year I will reach the speed of light. Then in couple of more years of travelling I will cross the universal speed limit !! Am I right ? Is it even possible ? Will I time travel to past ?

[@skymonkey1332]

My head actually hurts trying to think about this.

[@yukterez]

The edge of the observable universe is not the Hubble radius or the age of the universe x c (13.8 GLyr), it is the Particle horizon which is 46 billion lightyears away. The farthest distance one can travel is nevertheless 17 billion lightyears in comoving coordinates, see physics.stackexchange.com/questions/256441/considering-dark-energy-and-other-factors-what-is-the-most-distant-object-light/256948#256948

[@whatelseison8970]

Well, I've always wanted to see Neptune. It's so beautiful I can hardly believe it's actually a real place out there in space. According to the calculator you mentioned, getting out to Neptune at constant "perceived" acceleration would take a mere 45 days topping out at some 0.7% c with scarcely any time dilation. This might even be possible with some variant of a project Orion nuke rocket (or Rock-nuke-et). But I wouldn't stop there, oh no. I'd like to be excused from the human race I'm gonna save up every penny to get blasted into space I'd like to watch the world revolving from a comfortable place On my interstellar, Russian-built home base Because I aint got no privacy or peace of mind I don't sleep and I smoke cigarettes, I'll be dead by twenty-five But if nobody ever listens then nobody ought to mind It's not your fault, I'm just not one of your kind.

[@Caseylawton]

Stop smoking

[@whatthefunction9140]

How would this all be different if I was in a centrifuge that was accelerating at 1 G? Would I only feel 1 G as my velocity increased?

[@TiagoTiagoT]

I wanna know that too

[@josephpowell6009]

it all made self consistent logic until this comment

[@DJASenOfficial]

In space you would but not on earth with gravity acting upon you.

[@dustintaber]

I've been trying to wrap my head around this for years. How the heck did Einstein think this up!?

[@frasercain]

The key idea what holding the speed of light constant. Once you get that part nailed down, the rest makes more sense. :-)

[@Rio-musictopic]

How long would it take to travel 63 light years?

[@JonathanLaRiviere]

2:50 *the second-nearest star 😅 … seriously my bad, I just read Project Hail Mary, and he tries to stump his class of junior highers with this trivia

[@jameskilrain38]

Knew this.They must even adjust the GPS satellites for time dilation.Time is slowed down by gravity as well as speed.Clocks run faster at the top of the Empire State Building.Near a black hole the extreme gravity would slow time.Of course,it probably rip you apart as well.Anyhow,this idea have been used in science fiction,as well.Such as Planet of the Apes and others ,for example.Still,a good video.

[@ItsAbrahamSamuel]

Interesting

[@dark808bb8]

Hey, how much time needs to pass until the universe's expansion has accelerated so much that between each second a 1 meter of space becomes 2? Will the universe ever tear a proton apart?

[@tanmay996]

+FraserCain How much energy do we need to power a spaceship of that capacity?

[@frasercain]

+Tanmay Mehta If you use that calculator, I mentioned, it actually shows you. But bottom line, all the energy in the Universe.

[@blobdragon2678]

+Fraser Cain ahhhhh,now that you mentioned it, i actually think that i have one in my pocket. *hand you "all he energy in the universe"* take care off it.

[@blobdragon2678]

so what happens if i travel for 1 day or hour? how long would have passed for the rest of humanity

[@frasercain]

+Eyob Tadessa It depends on your speed. If you're going fast enough, millions of years could pass for humanity during a single hour for you.

[@blobdragon2678]

Fraser Cain but in you're video, you traveled at 95% of the speed of light, over a 3 year distance. and you managed to travel 3 year's in the future. so how does it work that i can travel milion's of year's, in just an hour? or does the acceleration of time get MUCH MUCH bigger when you go at 100%(if possible). and if you managed to go faster then the speed of light, what would happen, (imagine that it's possible) if i traveled 150% of the speed of light, would i still be traveling forward in time? thx in advance

[@floridaman2000]

I am sorry if I am not smart about this but if i travel fast enough in the 1 hour example here I would only have expeirenced 1 hour of time but everything on earth would have aged millions of years? and would i be millions of years old myself? according to earth time standards?

[@marwinando]

I wouldn't mind traveling out into unknown space and come back to earth a few hundred years later!

[@kimursin5374]

So if we can travel at lightspeed and send probes or spacecrafts to explorer, then we cant have the results? Unless we do sometime of timetravling to? I guess that put a limit for our Star Trek Federations plans......

[@jaredheight3686]

Thanks Fraserstein

[@frasercain]

Glad to do it.

[@cassideyousley406]

Mind nuclear detonated...

[@frasercain]

That's some next level mind blown.

[@highchamp1]

Echhh Sitting on my Tuchas for that long? Forget about it!

[@frasercain]

+highchamp1 That's it, you're not concerned about leaving all your loved ones behind? I agree, though. 45 years of boring space travel is pretty hard time to do.

[@pretense101]

I loved the story ,if we, could we, but can we no but I have always thought magnets or a magnetic field could take you there, my story .

[@AGMediaNL]

Obviously I'm not Einstein and sorry if I missed something, but I would love to understand this theory. (assuming you have an insanely powerful telescope). When you travel from Earth with the speed of light and look back at the Earth, it will look like time is standing still on Earth since the light "hitting" your eyes is traveling at the same speed as you do. When you go faster than light and look back at the Earth, "time" will run backwards from your perspective since "older light" is hitting your eyes. You can see your younger self on Earth. When you are flying faster than light back towards Earth from far far away, things will fast forward from the younger you/world to the modern you/world. When someone from Earth is looking at you blasting off faster than light speed, you will be instantly gone from his perspective. When he looks at you coming towards Earth faster than light, it will look like you go WAAAAAY faster than that. Still on the right track here, right? :D Then I don't get what traveling at light speed or faster speeds has to do with time changes other than a logical changed perspective on what you SEE from where you are "standing". Therefor I can't let it go that if I travel 5 years at the speed of light (or faster) and 5 years back, people on Earth will not be older than 10 years. Ofcourse there might be forces that causes age differences/ time perspectives, but "travel speed" and "light" feels very unreal and unlogical. HELP! :D

[@AGMediaNL]

So basicly, if you are at the edge of the observable universe like you say, Earth isn't billions years older, but younger. It isn't, though... but it would look like it since it's old light hitting your eyes. You fly back in that direction with the same speed you traveled away and the Earth will be back as it was (only 90 years later since that is your travel time in total).

[@PeteyParkz]

Andries de Haan I feel the same way. Also, if you were to go faster than the speed of light, wouldn't every thing suddenly flip around 180degrees and THEN start going backwards? Because the backs of old photons would be hitting your retinas rather than the fronts of new ones? MIND BLOWN

[@TiagoTiagoT]

The faster you go, the more your time slows down relative to the rest of the Universe. We've actually tested it with a pair of atomic clocks, one left on the ground, and one flown around the Earth on airplane; the one that flew fast was some tiny fractions of a second earlier than the one that was left still.

[@AGMediaNL]

***** Ok, interesting. Is it clear why it happened? Or is that still a speculation/ theory? Can it not be the case that it isn't "time" that changed, but simply the atomic clock that "behaves" different in that situation? It's still just a device, ofcourse. A watch (not to compare it with an atomic clock ofcourse) can be affected by magnet fields for example. Not trying to be a wise-ass here, btw. Truly interested. :)

[@TiagoTiagoT]

I'm not too familiar with the details of the experiment, but atomic clocks are considered one of the most accurate ways we got to measure the passage of time. GPS satelites use them to compensate for the time speed difference they got due to their orbital speed; we wouldn't be able to get as precise locations thru GPS if things were working in a different way.

[@Orthodoge]

id be willing to go to a few close stars that take less than a couple decades(from earths perspective)

[@frasercain]

What about with time dilation? Would you be willing to if it meant everyone else experienced a few hundred years?

[@taniagoswami4821]

Can man actually ever reach the edge of the universe? The universe is constantly expanding because of the dark energy at an exponential rate.

[@frasercain]

No, there are parts of the Universe that'll be expanding away from us faster than the speed of light.

[@MrVillabolo]

I hate to throw in a spanner into relativistic flight but I heard that an object will increase in mass as it goes faster. Eventually, it would implode into a black hole. Long before that were to happen the effects of mass increase would have impacted any biological organism by making it much 'heavier'.

[@frasercain]

It all depends on your perspective. From the person on the spaceship, they won't turn into a black hole.

[@TarasBoychuk]

if light travel from/to Andromeda 2.5 million light years (Earth coordinates) how it takes a spaceship 33 years? Does it mean that from photon perspective it travel less than 33 years?

[@frasercain]

For a photon, the trip takes zero time.

[@philmetal9604]

If a star we see in the sky is 100 light years away and goes out. Does it take 100 years for that light to not be seen in our sky? Or does it "go out" at that same instant

[@frasercain]

That's right, it takes 100 years for the star to disappear from our sky.

[@thecaptain2281]

@4:15 The universe is 13.5 byo[which is still open for debate], but it's expansion from the central point of the big bang has already exceeded the speed of light and is continuing to accelerate. Given the estimated curve of acceleration from the point of the big bang to the present, the universe is currently over 57 billion light years wide, measured from outer edge to outer edge. But Earth is near the outer edge of the universe, 3.7 billion light years away, approximately. So if someone departed earth as you described it, heading toward the closest point of the edge of the universe, it would only take them 5.3 billion years, from our perspective accounting for continued universal expansion. Now if they departed from the central point of the universe heading toward the outer edge it would currently take 28.5 billion years, assuming the universe suddenly grinds to a halt, expansion wise. But it won't. The base problem with the situation you presented is that it simply will not work. Anything traveling the speed of light[such as light itself or your theoretical ship] leaving the center of the universe will never reach the outer edge because the universe is expanding at a speed greater than the speed of light relative to the center point of the big bang. This is why astronomers literally can't find the center of the universe, and they likely never will. We have already accelerated away faster than it's light can ever reach us. The Milky Way galaxy[or it early progenitor] lost sight of the opposite side of the universe a few thousand years after the big bang and then of point of the big bang itself 6.3 billion years ago, long before the earth came into being. And as the universe continues to expand, we will loose sight of more and more of the inner universe.

[@eltedioso]

"This is doctor Fraser Cain... I'm listening.."

[@peterpalumbo1963]

I would have to think about relativistic travel, even if it is some how possible. I can handle the time but what about the people I leave behind. The only real solution is the Acuberra drive where space is expanded and contracted and the ship does not move.

[@mrbedsocks1]

is there any way you could get around the time?

[@frasercain]

No, if you're going to travel quickly, you're going to experience time dilation.

[@mrbedsocks1]

Even with a warp drive?

[@frasercain]

No, if you can invent a warp drive, then you can avoid time dilation.

[@doncarlodivargas5497]

one easy way to get back to your family and friends again after travelling for trillions of years through space, to the edge of the universe, would be to drag a worm hole with you by the space ship, so, when you decide to travel back again you simply return trough the worm hole, not space, and since travelling through the worm hole bring you back in time you will be home for dinner, only remember to bring back a little something, as a souvenir for the folks back home, you have been a long way from home and they expect a present

[@stevenirizarry1304]

This is true...fun fact...your family could easily shoot a micro-wormhole In your direction with a particle accelerator and over a few weeks they will see that this thing is zipping past the universe very quickly and than they will see you. They would create a portal a billion years into the future