New perspective on Time Travel?

In summary, the sky and stars as we see them are not the same as they were in the past because the light has taken some time to reach us.
  • #1
Marco12
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I was looking at the sky and I began to think about the stars. Obviously they emitted their light years ago because as we know, light is fast but not instantaneous. That the sky and stars as we see them, are not anymore because its only a view of their light omitted years ago. My point is that we are essentially observing the past every time we look at the sky.

If we are essentially observing the past every time we look at the sky, does this prove time travel beyond any doubt? I mean if we were to create a "machine" to take us instantaneously right at the stars as we perceive them, we would go to a place back in time. Am I making any sense? Sorry guys but I am basing all this on my thoughts.
 
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  • #2
Marco12 said:
If we are essentially observing the past every time we look at the sky, does this prove time travel beyond any doubt?
Yes, we're observing the past via starlight. And that has nothing to do with what I'm supposing you might mean by 'time travel'.

Marco12 said:
I mean if we were to create a "machine" to take us instantaneously right at the stars as we perceive them, we would go to a place back in time.
Sure ... IF. And IF I could foretell the future, then I could get rich at the racetrack.

Marco12 said:
Am I making any sense?
Not really.
 
  • #3
No, that's not time travel as people argue. We are seeing what the stars emit to us. If there were an earthquake at the center of an ocean, the waves we would get on land would just be signals that took time to reach us. We could even gather all the wave data and figure out where the earthquake took place, how it took place, and at what magnitude. We in a sense, can "see the earthquake". However, if we were then able to instantly go to where the earthquake was, it would be gone.

The real point to time travel would be to detect the water waves and some how be able to put yourself at the earthquake before or while it's happening.
 
  • #4
ThomasT said:
Sure ... IF. And IF I could foretell the future, then I could get rich at the racetrack.

No. If you receive the starlight, then that is what the star was doing X million years ago or what have you. If you were able to instantly go to that star, you would see what the star would be doing after having lived for another X million years.
 
  • #5
Marco12 said:
I was looking at the sky and I began to think about the stars. Obviously they emitted their light years ago because as we know, light is fast but not instantaneous. That the sky and stars as we see them, are not anymore because its only a view of their light omitted years ago. My point is that we are essentially observing the past every time we look at the sky.

If we are essentially observing the past every time we look at the sky, does this prove time travel beyond any doubt? I mean if we were to create a "machine" to take us instantaneously right at the stars as we perceive them, we would go to a place back in time. Am I making any sense? Sorry guys but I am basing all this on my thoughts.


If this is time travel, then I undergo time travel each time I receive a letter mailed several days ago.

Zz.
 
  • #6
ZapperZ said:
If this is time travel, then I undergo time travel each time I receive a letter mailed several days ago.

Zz.

Well stated.

Just because we are just now seeing it doesn't mean that it is the present. It's like when you watch "live" tv and there is a 2-3 second delay between what is going on to the people there and what is on the screen. If I was watching a basketball game and could instantly transport to the court. I still couldn't use that to jump right in front of an opposing player at the moment I am seeing him take the shot on my tv.
 
  • #7
Pengwuino said:
No. If you receive the starlight, then that is what the star was doing X million years ago or what have you. If you were able to instantly go to that star, you would see what the star would be doing after having lived for another X million years.
Yes of course you're correct. If we could instantaneously go to a star millions or billions of light years away that we are seeing now via its light as captured by our telescope, then we would probably see something quite different than we had seen in the telescope.

I was making the 'IF' point and overlooked a most important detail. Thanks for the correction.
 
  • #8
ZapperZ said:
If this is time travel, then I undergo time travel each time I receive a letter mailed several days ago.

Zz.

What in the world do you mean by 'time travel'?
 
  • #9
Phrak said:
What in the world do you mean by 'time travel'?

Shouldn't you be asking the OP that question? I merely cited another example analogous to his/her scenario. *I* do NOT consider this to be "time travel".

Zz.
 
  • #10
I always remember my physics teacher explaining that if we could create a craft to travel to the 'edge of the universe' (instantaneously), we could 'look' back in and see how the universe began.

Not time travel, but still something I found interesting purely because I'd never thought of it like that. Not sure how accurate the statement is though.
 
  • #11
Marco12 said:
I mean if we were to create a "machine" to take us instantaneously right at the stars as we perceive them, we would go to a place back in time.

Negative, friend. If you could travel to them instantaneously, you would be close to the source of the light. The light you see at that point would no longer be delayed by the extreme distance. Instead of seeing old light, you would simply see "current" light.
 
  • #12
Phrak said:
What in the world do you mean by 'time travel'?

Zz made an analagous scenario to the OP's scenario. So, if the OP's scenario thinks his is time travel, then he must conclude that Zz's is too. Since it is obvious that Zz's is not, then the OP's obvious is not either.
 
  • #13
DaveC426913 said:
Zz made an analagous scenario to the OP's scenario. So, if the OP's scenario thinks his is time travel, then he must conclude that Zz's is too. Since it is obvious that Zz's is not, then the OP's obvious is not either.

I call false reverse-correlation by demonstration!

Although I happen to agree entirely!
 
  • #14
FlexGunship said:
I call false reverse-correlation by demonstration!
:smile:
It's not an attempt to show an if ... therefore. It is simply that, in examining why the mail scenario does not constitute any form of time travel, one realizes on one's own that simply accepting the delay in transmssion of any signal does not constitute time travel.
 
  • #15
Did all of you missread the op's post on purpose? When he says:
Marco12 said:
if we were to create a "machine" to take us instantaneously right at the stars as we perceive them
he obviously means that you would be taken to the star you see which would be time travel and not the star that is sending out light as he is making the observation which would not be time travel.
ZapperZ said:
If this is time travel, then I undergo time travel each time I receive a letter mailed several days ago.

Zz.
No, you would be time traveling if you had a machine that could intantly take you to the guy who wrote the letter when he is writing it.

The problem is that we can't make such a machine, at least not with what we know today.
 
  • #16
Klockan3 said:
Did all of you missread the op's post on purpose? When he says:
he obviously means that you would be taken to the star you see which would be time travel and not the star that is sending out light as he is making the observation which would not be time travel.

No, you would be time traveling if you had a machine that could intantly take you to the guy who wrote the letter when he is writing it.

The problem is that we can't make such a machine, at least not with what we know today.
If interpreted that way, then his question makes even less sense. He would be saying "if I could invent a magical machine that could go anywhere instantly, then that proves time travel does exist."


Note that the mention of the magical device is the very last line of his post, long after he has stated his case. I see that as merely an attempt to corroborate his idea, not form the basis of it.
 
  • #17
I think we've all missed the point because we haven't tried hard enough to understand which or what mis-step Marco12 may have made in his scenario, myself included.

However, I'm not inclined to place much weight in any of-course-not disclaimers to "time travel" as it is commonly perceived. Everything I've heard or read is ad hoc, generated to protect the notion that logical contradictions occur in the son-kills-father-before-son-is-born story, so must be discarded. This sort of logic is just as caustic to quantum mechanics, and should receive similar treatment by those that so easily willing to dismiss time travel.

I suspect Marco might be a young optimist. I could be wrong. But if we would, for a moment, place no limits on human ingenuity, and expect that there is some way in which people could find a way to exceed c, then Lorentz invariance implies contra-causality. I'm not implying that this is do-able, but just that this sort of presumption may be the origin of Marco's idea.

So, Dave, I was more interested in what Zapper had to say about the subject.
 
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  • #18
I blame history/discovery channel for these sorts of misconceptions. In their astrology and cosmology type documentaries they often talk of "seeing into the past" when looking at distant stars, since indeed what we are seeing is something that occurred ages ago, and it is easy to get caught up in the magic of it all, seeing something from so long ago and far away, and convince ourselves that we are actually "seeing into the past."

It's not that the phrase is inaccurate, but that it's not a scientific statement at all, rather a metaphorical or poetic statement about what we are looking at.

But it's merely that a star throws a photon at you and it takes awhile for your eye to catch it. This is no more time travel than, as Zapper said, receiving a letter that was sent which takes you awhile to receive.

When you watch a video on youtube, are you "seeing into the past?"

When you read a novel by Charles Dickens are you "seeing into the past?"

In our imagination it can feel like it. But what we are witnessing is simply the current effect of an even that happened in the past. It's just that this fact is exaggerated by the immense distance of the stars and the immense time that has passed. I think this mystique is not even lost on physicists and astronomers who know very well what is actually happening.

Without this exaggeration the fact that we're not seeing into the past becomes more obvious. If you look at the sun (don't) you're seeing light from 8 minutes ago. This is still pretty remarkable, but perhaps not so much as billions year old light. If you're gazing at the moon you are seeing light from about 1.3 seconds old. If you are looking at a light on a street, a light in your room, your computer monitor or anything at all, you are looking at light that was emitted at some time in the past.

To me the most amazing thing is that we can't see anything BUT old light. Perhaps this is what leads to misconceptions about time travel. But again - it's just that a thing throws a photon at you and it takes some time for your eye to catch it. That's all.

The second mistaken idea was " I mean if we were to create a "machine" to take us instantaneously right at the stars as we perceive them, we would go to a place back in time"

It was answered by Pengwuino:

No. If you receive the starlight, then that is what the star was doing X million years ago or what have you. If you were able to instantly go to that star, you would see what the star would be doing after having lived for another X million years.

And Flexgunship:

Negative, friend. If you could travel to them instantaneously, you would be close to the source of the light. The light you see at that point would no longer be delayed by the extreme distance. Instead of seeing old light, you would simply see "current" light.

Which say the same thing, though the first explanation took me a few reads to get what he was saying, as it seemed to imply the future "another X million years." But of course he was referring to the present ("current") light. Sometimes I just read too fast.

I think I've managed to grasp the OPs line of thinking here. "If when we look at stars, we're looking at the past, then by going instantly to the star we will instantly go back to the past."

But I think this should be clear now. "Looking at the past" just means it took your eyes awhile to catch the light that was sent at a later time. Over at the actual star, there is nothing extraordinary happening time-wise. It's just throwing more photons all over the place including in our direction.

By going instantly to the star you'd basically be getting a head start on what we earth-people would see some billion years later. If I send Zapper fan-mail once per day, it takes him 3 days to receive it and he receives one letter per day. If he travels instantly to my location, he may catch me in the midst of writing another letter. Before he can tell me to stop this creepy behavior I have already dropped the letter into a mailbox which zapper cannot get into. After throwing up his arms in frustration, he goes home, and three days later he receives that same letter. At no point did he travel into the past, but it did take him awhile to receive the letter.

Similarly if I travel instantly to a star I will see photons that are being thrown my way, and when I instantly go back home I will see those same photons a few billion years later (when I'm in the ultra-old folks home).

-DaveKA
 
  • #19
So what ramifications does Quantum Mechanics have on this discussion? Wave-function collapse must happen before our eyes catch the affiliated photons. Since we are always looking into the past, does this mean that we can also change it? For example, imagine the double-slit experiment set up one light-year away from Earth. By observing the interference pattern from this distance, and thus forcing the photons out of a super-position, you are essentially changing the behaviour of photons that existed one full year ago. Now isn't that changing the past?
 
  • #20
Pretty Pony said:
So what ramifications does Quantum Mechanics have on this discussion? Wave-function collapse must happen before our eyes catch the affiliated photons. Since we are always looking into the past, does this mean that we can also change it? For example, imagine the double-slit experiment set up one light-year away from Earth. By observing the interference pattern from this distance, and thus forcing the photons out of a super-position, you are essentially changing the behaviour of photons that existed one full year ago. Now isn't that changing the past?

To be blunt, no.

The photons exist now when we observe them a light year away. They are one year old.

That's like saying the aircraft that traveled from london to new york hasn't aged during the duration of the trip and interfering with it in new york affects it when it was back in london (i detonate a bomb in ny and it explodes on the runway at heathrow).
 
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  • #21
Not that I am suggesting it at all possible or anything of the sort, but perhaps some ideas of retrocausality could apply here?
 
  • #22
Dougggggg said:
Not that I am suggesting it at all possible or anything of the sort, but perhaps some ideas of retrocausality could apply here?

Why?

What makes the OP scenario different to ZapperZ's snail mail one?
 
  • #23
Pretty Pony said:
So what ramifications does Quantum Mechanics have on this discussion? Wave-function collapse must happen before our eyes catch the affiliated photons. Since we are always looking into the past, does this mean that we can also change it? For example, imagine the double-slit experiment set up one light-year away from Earth. By observing the interference pattern from this distance, and thus forcing the photons out of a super-position, you are essentially changing the behaviour of photons that existed one full year ago. Now isn't that changing the past?

No, but cool idea. :) Could work in sci-fi!

Again this phrase "looking into the past" is a metaphorical one.

There's a sense in which it's true. According to http://en.wikipedia.org/wiki/Speed_of_light" [Broken] (we know Wikipedia is completely accurate all the time) the light from an object 1 foot away takes 1 nanosecond to arrive.

So if you're looking at an object 10 feet away, you're seeing what happened 10 ns ago. The closer you get, the closer in real time you get to the object, but since the speed of light is finite, you will never really see the *object* in real time.

However, what you're really seeing is not the object, but the *light* from the object when it hits your eye. That is a current, real time event.* What's happening *now* is that the light is hitting your eyes.

I'm just using a basic thought process here (which I think is pretty logical) and not really thinking about QM. I'm not sure how to describe this in terms of the observer effect. If something is a billion light years away, anything you do to change it is going to take (at least) a billion light years to have any effect, and you won't be able to see the result for another billion years. (Somebody correct me if I'm off here).

-DaveKA


* Yeah, it might take a little bit for your brain to process the light information, and to figure out what the object is, but that's another discussion.
 
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  • #24
jarednjames said:
Why?

What makes the OP scenario different to ZapperZ's snail mail one?

I was more just trying to play the role of devil's advocate. I think ZapperZ's example was perfect. I just wanted to make sure we at least covered all possible ideas in this concept.
 
  • #25
dkotschessaa said:
I'm just using a basic thought process here (which I think is pretty logical) and not really thinking about QM. I'm not sure how to describe this in terms of the observer effect. If something is a billion light years away, anything you do to change it is going to take (at least) a billion light years to have any effect, and you won't be able to see the result for another billion years. (Somebody correct me if I'm off here).

If you change the object a billion light years away (let's say we destroy a star somehow) then it will take a billion years before we see this change reflected in the sky.

However, if we simply 'change the light' as we see it here, a billion light years away from the source, it doesn't affect the source of the light in any way.
 
  • #26
jarednjames said:
To be blunt, no.

The photons exist now when we observe them a light year away. They are one year old.

That's like saying the aircraft that traveled from london to new york hasn't aged during the duration of the trip and interfering with it in new york affects it when it was back in london (i detonate a bomb in ny and it explodes on the runway at heathrow).

It was not those photons that I was concerned about; just the ones with the interference pattern on the screen. Perhaps I should use a less ambiguous scenario:
Now imagine a small sampling of Cesium-134 (134Cs) floating around in space, one light-year away. With a very powerful telescope, one can change the rate of the radioactive decay by observing it, because of the Quantum Zeno effect. One year ago, this Cesium sample suddenly stops decaying because you are observing it now. Blink, and for about 300-400 milliseconds, it continues to decay. This would be changing the past, no? I'm sure there would be some application of the butterfly effect to this thought experiment, but I don't know a great deal about radioactive decay. Suffice to say that these observations may cause the Cesium to reach its first half-life sometime last September, rather than last July. That, surely, is changing the past? Note that in real time, once you start observing the Cesium, it already reached its first half-life in July. As you observe it, you change this date to sometime in September, thus changing events that have already transpired in the past.
 
  • #27
So every time we look up at the stars we extend their life?

I think someone more qualified on the subject should pick things up from here.
 
  • #28
Pretty Pony said:
So what ramifications does Quantum Mechanics have on this discussion? Wave-function collapse must happen before our eyes catch the affiliated photons. Since we are always looking into the past, does this mean that we can also change it? For example, imagine the double-slit experiment set up one light-year away from Earth. By observing the interference pattern from this distance, and thus forcing the photons out of a super-position, you are essentially changing the behaviour of photons that existed one full year ago. Now isn't that changing the past?

This is the upshot of delayed choice quantum eraser experiments - probably what you were thinking about here. By looking at ancient star-light, we are indeed collapsing its wave function and so some kind of retrocausality has to be factored into a fuller model of time.

http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment

The letter analogy works for macroscale classical objects, but QM does say there is more to the story.
 
  • #29
apeiron said:
This is the upshot of delayed choice quantum eraser experiments - probably what you were thinking about here. By looking at ancient star-light, we are indeed collapsing its wave function and so some kind of retrocausality has to be factored into a fuller model of time.

http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment

The letter analogy works for macroscale classical objects, but QM does say there is more to the story.

Called it.:approve:
 

1. What is the new perspective on time travel?

The new perspective on time travel is the idea that time travel is not only possible, but it may already be happening. This perspective challenges the traditional view that time travel is purely science fiction and explores the possibility that we may one day be able to travel through time.

2. How does the new perspective on time travel differ from the traditional view?

The traditional view of time travel is based on the idea of traveling to the past or future through a machine or device. The new perspective on time travel suggests that time travel may not require a physical device, but instead could be achieved through manipulation of space-time or through consciousness.

3. What evidence supports the new perspective on time travel?

There is currently no concrete evidence to support the new perspective on time travel, as it is still a theoretical concept. However, some scientists point to phenomena such as time dilation and the possibility of parallel universes as potential indications that time travel may be possible.

4. What are the potential implications of the new perspective on time travel?

The new perspective on time travel has the potential to revolutionize our understanding of the universe and our place in it. It could also have practical applications, such as allowing for communication with the past or future, or even changing the course of history.

5. What are the challenges and limitations of the new perspective on time travel?

There are many challenges and limitations to the new perspective on time travel, including the lack of concrete evidence, the potential paradoxes and complications that could arise from time travel, and the technological and ethical considerations involved in actually making time travel a reality.

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