[removed]

From everything we know, you can only travel forward but not backwards

NDT said there are general relativity equations that make it possible, but paradoxes make it impossible. This is why im saying maybeee yes it is possible, but we won’t be whole in the past, only a hologram that no one can see, in an upper dimension maybe?

aee you suggesting that ghosts are holograms from the past/future cause that sounds lit

I like to consider the idea that time travel may be possible through a sort of gate, and that no one has traveled to the past so far because the earliest you can travel is to the creation of the first gate. But once the first is built, the floodgate will be opened and people from all times will be appearing through it.

In terms of only traveling via observation, there is an excellent short story by Asimov about this very thing.

Noo, not at all. Im just saying maybe they are holograms, but just compared ghosts to holograms

Thank you!!

For starters, it’s not possible and never will be possible. If it were, what kind of physical mechanism would cause a hypothetical traveler to be invisible and intangible, but also allow them to observe? Unless we’re talking about multi-dimensional stuff, but that’s going far beyond the initial hypothetical.

Christians will travel back to try and witness the birth and life of Christ.

Paleontologists will travel back 65 million years to observe dinosaurs and see how they really lived and what color they are.

Historians will go back to times all over to witness historical events in real time.

Ordinary people will travel and try to warn their past selves in order to possibly improve their present. And they will try to change events to improve things.

What if the only mechanism that allows us to travel to the past is this though, wouldn’t it solve the paradoxes?

The ordinary people part wouldn’t apply I guess, I mentioned that you cannot interact, but only observe, the rest does make sense though

[removed]

Not saying that it's impossible but it's gonna be a one way trip, which opens up a branch in the timeline/creating another reality, in this way there's no paradox occurring. Just endless multiverse or timeline

Wouldn’t time travel boop you into space? You could go backwards let’s say, but would your let’s just go with incorporeal body remain completely still to do it? The Earth is in a wobbly orbit around the sun and rotating as well.

If you wanted to visit another time let alone place accurately you’re going to need some way to move your position as well. Otherwise you stand the chance of only being able to visit very particular times and even then, who knows what part of the world you might end up in if calculations are slightly off.

Oops I’m underground, in the sky, ocean, or just floating in space.

This would be the same as viewing the past. I don't know if that qualifies as time travel. When you look at stars, you are looking at their past. Betelgeuse may have already blown up, but we don't know it yet because light from the explosion hasn't reached us yet. It is 642.5 light years from Earth. Holograms are usually visible, so I'm not sure what definition of hologram you are using.

Hypothetically, I guess? But it’s not much of a solution if there is nothing to explain it physically or mathematically. You’d have a better shot arguing divergent timeline theory than basically ghosts.

> Wouldn’t time travel boop you into space?

You can set your inertial frame such that the device is considered the motionless center of the universe, and everything else moves around it. It would be some complex physics, but then so would time travel.

[deleted]

If we were holograms, how would the photons interact with our eyes causing us to be able to see everything yet nothing else in the universe at that time interacts with us.

[removed]

So only the exchange of information between past/present is possible, but the exchange of or transfer of matter between two times is not? Sounds legit.

Ah yes the classic, “space moves around you” so just do /that/ with time.

>Heard a bunch of scientists talk that paradoxes make it impossible

There's nothing about time travel into the past that is logically impossible, as there are ways to get around things like the Grandfather Paradox.

The Novikov Self-consistency Principle, for instance, allows travel to the past by positing that no actions taken by time travelers will be able to alter the timeline in any way, as a matter of principle. A lot of people interpret this as some spooky godlike mechanism that's watching you and tweaking things to keep you from messing everything up, but that doesn't have to be the case. A better way of looking at it is that your time travel journey has always been part of the past from the get-go, as something that's always been inherently and deterministically baked into the fabric of the universe. In other words, your time travel actions will inherently be compatible with a logically coherent universe by virtue of you being able to time travel at all. This is easier to intuitively appreciate in the context of a block universe model of time, which is what arises from modern physics.

Some people don't like this because it implies that we have no free will, but there's no good reason to believe that we have libertarian free will in the first place. Try as you might to kill your grandfather, it's just part of the structure of the universe, which transcends your illusion of free will, that you will not succeed in doing so.

Another conceivable possibility deals with alternate timelines altogether, like with the Interacting Many Worlds theory of quantum mechanics, in which backwards time travel events force you into a quantum leap of sorts into another universe altogether, which you're free to "mess up" however you like.

All of this is assuming that time travel into the past is physically possible, of course, which is a real big assumption and currently an open question with grim prospects.

To be fair, many things that science once said were impossible are now possible, which means that science isn’t always right.

Science can only theorize based upon the evidence it has at the time the theory is made. New discoveries and advances in technology can render past theories inaccurate.

Point is, never say never. As the saying goes, we don’t know what we don’t know, and I’m willing to bet there’s a whole universe of things we don’t know.

This isn't the realm of science to talk about things like ghosts. If it can't interact with our reality in any way, it's questions we fundamentally cannot address.

Why not? We still know little about that. What would make it impossible

Might be a reach but what about memory.

In memory we can be an invisible and intangible observer. If we really put a lot of effort into a moment, can't that memory almost be like a picture, even a video ?

This is the beginning of figuring out how to access a part of the timeline we are no longer apart of

Thank you! That was very informative!!

Occam's razor comes to mind.

If you're interested in learning more about time and time travel, here are a couple of amazing books on the subject:

From Eternity to Here: The Quest for the Ultimate Theory of Time (2010), by Sean Carroll (in my opinion, the best book on the physics of time)

A Brief History of the Philosophy of Time (2013), by Adrian Bardon (in my opinion, not only the best book on the philosophy of time, but the best on time ever written for the general public, and I've read quite a few)

EDIT: Fixed link.

I’ve seen it suggested that time as we perceive it is just a result of how gravity distorts with space time.

I interpreted that as basically time isn’t real and it’s just something our brains concocted to understand the natural universe

So I don’t think traveling or projecting a hologram into the past is possible because time as we think we understand it isn’t actually a thing

[removed]

Ah, Novikov Self-Consistency Principle, that’s what it’s called. I’ve always just called that idea ‘the way time travel works in Harry Potter’.

Hello u/Perseverxnce, your submission "What if time travel to the past was possible?" has been removed from r/space because:

• It is not related to space.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.

I think the issue with time travel is as far as we know now, black holes have the ability to “distort” time. From an observer’s viewpoint outside the black hole, time will appear to stop.

But contrary to how many popular sci-fi movies portray it, it’s not like you go through the black hole and come out on the other side in a different time frame. The cessation of time only exists within the black hole.

The idea of wormholes (which have never been proven to exist) also posits the same idea of being able to manipulate time. But even theoretically, they have the same problem as black holes. Time can only be distorted within the wormhole.

I won’t say it’s impossible, but it’s going to take an enormous amount of technological and intellectual advancement to make time travel possible. If it happens, I doubt people are going to be interested in time traveling to the past.

Considering the amount of resources that would be necessary to accomplish this, it would make far more sense to time travel to the future, not the past. I know a lot of sci-fi movies focus on the idea of time traveling to the past to make meaningful changes that will impact the future.

But if you look at it realistically, it makes more sense to expend resources time traveling into the future, not the past. Time traveling into the past presumes you can change the past to impact the future. But that’s a huge gamble.

We would be better off traveling into the future, to see what’s happening there, so we can better prepare for it. Or perhaps make changes in the present, that can positively benefit our future.

[removed]

>We would be better off traveling into the future, to see what’s happening there, so we can better prepare for it. Or perhaps make changes in the present, that can positively benefit our future.

But then you'd have to travel back into the past again so you can let everyone know what's going to happen ;)

[removed]

[removed]

Based on the current prevailing theories I’m assuming we could only experience the future or past while in the black hole or worm hole. Then we leave the hole and are back in the present. In that context it would make sense to “view” the future, not the past.

Well, by far the easiest way to time travel to the future is just to go very very fast, then relativity will put you there without the need for wormholes, black holes and so on.

Of course, that's not reversible though, going very very fast backwards won't help.

Dunno about the black hole / wormhole approach, I'd thought there was no way of transmitting information across a black hole event horizon.

Worm holes might be another matter though.

[removed]

Here's a notion I've toyed with for a very long time. I'd appreciate any and all feedback from resident experts.

For context, most here are familiar with the claim that if one could instantly jump from Earth to a point 65 million light-years distant and looked back at Earth with a telescope of sufficient power, it would be possible to see dinosaurs roaming the planet's surface.

I am aware of some of the fallacies of this scenario. For instance, problems with photon resolution in seeing something as relatively small as a dinosaur. But, it still should be possible to recognize the Earth as an inhabited planet, even if only by shambling, unintelligent beasts. For comparison, just look at how many exoplanets have been discovered thus far and how much of these worlds we're able to learn even from such vast distances.

Now, assuming the above claim to be true, after calculating where Earth was at a given moment in the past, could one not then look at this point in space with a telescope and see a past Earth?