Brian Greene: Time Travel is Possible | BEST OF 2015 | Big Think

Brian Greene: Time Travel is Possible
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Theoretical physicist Brian Greene is fascinated by time. Is the time we experience in our day-to-day lives real? Is our interpretation of time actually how the world is structured? Could time be broken up into particles like matter? These questions fuel Greene's curiosity, and their most likely answers indicate that time travel into the future is very much possible. But traveling back in time, well, probably not. Greene explains why.
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BRIAN GREENE:

Brian Greene is an American theoretical physicist and string theorist. He has been a professor at Columbia University since 1996 and chairman of the World Science Festival since co-founding it in 2008. Greene has worked on mirror symmetry, relating two different Calabi–Yau manifolds (concretely, relating the conifold to one of its orbifolds). He also described the flop transition, a mild form of topology change, showing that topology in string theory can change at the conifold point.

Greene has become known to a wider audience through his books for the general public, The Elegant Universe, Icarus at the Edge of Time, The Fabric of the Cosmos, The Hidden Reality, and related PBS television specials. He also appeared on The Big Bang Theory episode "The Herb Garden Germination," as well as the films Frequency and The Last Mimzy.
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TRANSCRIPT:

Brian Greene: We know a lot about time. We know that time in some sense is, at rock bottom, that which allows change to take place, right. When we say that time has elapsed, we notice that because things now are different from how they were a little while ago. That’s what we mean by time elapsing. But is time some fundamental quality of reality or is it something that our brains impose on our perceptions to organize our experience into some coherent framework that allows us to survive? I mean I can well imagine that we have been under evolutionary pressure over the millennia to organize perception so that we can survive, get the next meal, plan for the future. All of that would seemingly require that we have a conception of time that we apply to what we experience out there. But that doesn’t mean time as we experience it is real. It doesn’t mean that time as we experience it is how the world is actually structured. I mean there are many ideas that people put forward. The possibility, for instance, that, you know, we all know that matter is made of molecules and atoms. Could it be that time is also made of some kind of ingredient? A molecule of time? An atom of time? Is that really what time is at a fundamental level?

Time travel is absolutely possible. And this is not some sort of weird sci-fi thing that I’m talking about here. Albert Einstein taught us more than 100 years ago that time travel is possible if you’re focusing upon time travel to the future. And I’m not referring to the silly thing that we all age, right. We’re all going into the future. Sure, I’m talking about if you wanted to leapfrog into the future, if you wanted to see what the Earth will be like a million years from now, Albert Einstein told us how to do that. In fact, he told us two ways of how to do it. You can build a spaceship, go out into space near the speed of light, turn around and come back. Imagine you go out for six months and you turn around and you come back for six months. You will be one year older. But he taught us that your time is elapsing much slower than time back on Earth. So when you step out of your ship, you’re one year older, but Earth has gone through many, many years. It can have gone through 10,000, 100,000, or a million years depending on how close to the speed of light you traveled.

And he also taught us if you go and hang out near the edge of a black hole, time again will elapse more slowly for you at the edge of the black hole than back on Earth. So you hang out there for a while, you come back and again you get out of your ship and it will be any number of years into the future, whatever you want all depending on how close you got to the edge of the black hole and how long you hung out there. That is time travel to the future. Now, of course, what people really want to know about is getting back. Can you travel back to the past? I don’t think so. We don’t know for sure. No one has given a definitive proof that you can’t travel to the past. In fact, some very reputable scientists have suggested ways...

[coosoorlog]

It is possible to travel back in time. It is called "visiting West Virginia".

[RickKasten]

It should be noted that just as there is no such concept of traveling through space without time, there is no concept of traveling through time without space. There isn't space travel and time travel; there is only travel though spacetime. If you traveled back in time just a week, you would find yourself emerging into empty space. Where you physically left our spacetime, the Earth will not have yet reached in its orbit around the sun, so there will be no Earth there to emerge into/onto. If you traveled back six months, you'd emerge not on the opposite side of the sun from where Earth would be but in empty galactic space, because the entire solar system is six months in the past of its orbit around the center of the galaxy. Six million years into the past, and you'd emerge in empty intergalactic space, because the entire Milky Way would not have traveled to that location yet. When you factor in the expansion velocity of the universe itself, who knows for sure where you'd actually reemerge at all!?

The entire concept of time travel is a misnomer. There is only travel through spacetime which we are already fully aware of (it's what we do every day), travel through space without the consequence of time and travel through time without the consequence of space, and Einstein's equations show us that the latter two are the same thing. What Greene refers to here as "time travel" isn't really time travel, it's merely the manipulation of time dilation in the presence of extreme velocity or extreme gravity which themselves only exist in the known spacetime. That's why it only works going into the future, because it's not actually time "travel" but exploiting the change in time velocity at those extremes.

[kaizersoze]

I remember seeing a video with this guy on the TAM 2011 panel with neil degrasse tyson, bil nye and kraus. One of the best debates I ever watched.

[G_G]

If traveling back in time became a reality nothing would ever get done and humanity would grind to a halt, because everyone would constantly be going back in time to fix every little mistake they make/have made or take every little opportunity they have missed, or use their current knowledge to constantly improve/upgrade their lives in the past.
And that's only talking about the personal lives... people also won't stop making changes in society, politics, economy, art, etc.

[sggod]

Powerful Brain Greene. I remember watching his string theory documentary when I was a teenager (like 15 years ago) and it was fucking mind blowing. I'm glad this guy is still around.

[raymonko]

Minutes 1:33 to 2:27 are missing from the transcript in the description.

[davidsipos]

I would like to ask you to rectify(do we use this word in this context?) my understanding of spacetime so here it is:
So what I've read/heard about spacetime I imagine it as a coordinate system with 4 axes, x y z and t. These axes have units we call planck length and planck time. If space is expanding does this mean that the endingpoints of the system are increasing or that the units are?And is 'the end of the timeline' or the length of the planck time increasing too?

[SNOWSOS]

I'd lean more towards time not technically existing, we just use it as a way to understand motion.

[Truthseeker]

Time is a product of space. Because going from one point to another takes, time.

[PeeedaPan]

i dont think its possible to time travel back in time because there are no people from the future here with us in the present.

[doodelay]

He has a conspiracy theorist, pseudo-sciencey vibe that just oozes out of every vid he's featured in. I know he's a legit physicist, but that quackish vibe is definitely real.

[cxa]

Look...I'm not saying that was aliens....but it was aliens.

[kellyorrichardweddle]

It seems evident that time passed, things changed, before our big brains were around. So time is not just a construct of the human brain.

[taschke]

after 7.5 yrs of obstaining while in the army, I got out and smoked a joint to celebrate. when I went to bed I started to pull the blanket over me, and I had that feeling I was being watched. it was dark, but in my minds eye, I saw an infinitely tiny race that I was about to crush. I watched them grow, thrive, spread, develope and discover who they were, what I was and what was going to happen. when we both made our peace with that, I rolled over them and went to sleep. Six months later, studying anatomy and physiology, I saw a picture of the topography of the nucleus of a cell and the pores through which RNA travel. I now study quantum mechanics. talk about spooky action at a distance!

[ericmann]

What role does precognition play in the bigger picture? Is it a form of time travel(in a sense it must be), or possibly paradoxical repetition of experience; observable only as a light echo that can be vaguely remembered? Is it some type of non linear electrical/energetic anomally offering indication of an ultra connected existential field ...and if so is that subtle proof of a highly flexible consciously projected reality?

Id say it easily could be viewed as communication between dimensions and more simply inverse, simple, and quantum ripples that can travel in any manner throughout the particulate/energetic field. These realizations can only defy the notion of an undisturbable 'one directional march of time', from a beginning point to an end point.

This subject greatly intrigues me because I personally experience precognition as a frequent occurance in day to day life. So much so, that I will never be able to view time as a finite ridgid entity. If there is a greater meaning or value in the experiences that I could personally divine it would be less relative to the content of the experiences and more how the experiences mock the veil perpetuating the illusion of solidarity of content. Its left laughably lucid and ambiguous; holographic even.
So I wonder: what more perfect understandings of time, dimensions, and reality are to come?

[mattyboy]

Time is relative to each molecule... the more mass something has, the more it distorts the space-time continuum around it. I think the grid spacing of a warped 3d space-time fabric would be closer, smaller, resulting in shorter time. .

I mean, doesn't that coincide with the theories of relativity? .
I've been wondering about time lately and a little social experiment arose in my head; if we were to gradually speed all media content up by like 3%, would we notice immediately, or would we evolve and speed up?

[rnaprimer]

I found a way to make time machine plz tell me where i should publish it.

[rvc]

I suspect that time is a manifestation of change.

[AdamShaiken]

Are you attempting to do a Capt. Kirk impression while conveying your highdeas, Brian ?

[AzaJabar]

And that what interstellar was all about