what we know about Time

[zapatos]

"if you take a close object, then propulse it far away, you are throwing the object into the past."

 

That is (edit-almost) correct. I never intended to say the throwned object made a time-travel.

 

Can you explain these two statements? I don't understand how something thrown into the past (from the present) did not travel in time. Are you saying that when you throw it into the past it also remains in the present? If so, that is even more confusing.

[michel123456]

I don't understand why you want to equate time and space. You can describe everything by only discussing space. Overlaying space with time only confuses things.

 

 

 

This is only true if space and time are the same. I guess I need to understand why you belive that. It just seems to add complexity with no benefit, and requires time to have properties that cannot be shown to exist. For example, if I throw a ball to you, it seems as if you are saying that it moves into the past (from my perspective), into the future (from your perspective) and not all through time (from the ball's perspective), all at the same time. Very confusing to me why it is true, and why you want to connect them in this way.

 

There is no confusion.

 

For example, if I throw a ball to you, it seems as if you are saying that it moves into the past (from my perspective),

yes absolutely.

 

into the future (from your perspective)

No no. The future is not observable, only if you are clairvoyant. from my perspective, the ball come from far to close, so it comes from the past to my present.

 

and not all through time (from the ball's perspective),

well, I am always in my present, you are always in your present, and the ball is always in its present. When the ball begins its travel from your hand, it shares its present with you. When the ball is half-way it sees (if it could see) you in its past, and I in its past too simply because only the past is observable from a distance. When the ball bumps my head, it shares its present with mine. That is not so complicated.

 

----------------

Or maybe you disagree with the statement that an object as observed from a distance is an object as it was in the past.

Edited March 5, 2012 by michel123456

[zapatos]

There is no confusion.

 

 

yes absolutely.

 

 

No no. The future is not observable, only if you are clairvoyant. from my perspective, the ball come from far to close, so it comes from the past to my present.

 

 

well, I am always in my present, you are always in your present, and the ball is always in its present. When the ball begins its travel from your hand, it shares its present with you. When the ball is half-way it sees (if it could see) you in its past, and I in its past too simply because only the past is observable from a distance. When the ball bumps my head, it shares its present with mine. That is not so complicated.

 

----------------

Or maybe you disagree with the statement that an object as observed from a distance is an object as it was in the past.

An object observed from a distance is a view of the object as it was in the past. The object itself is not in the past. It is still there right now. Just because I can't see how it looks today until tomorrow arrives does not mean it is in the past. I don't believe there are multiple copies of everything, one that exists now, one that exists yesterday, etc.

[D H]

Time is what clocks measure.

Not that you care about rep points, but +1 for that.

 

This, however, begs the question: WTF is a clock? I like to flip this statement around: Ideal clocks measure time. While this does not solve the "WTF is that?" kind of question ("WTF is time?"), this does define the concept of a clock in terms of what it measures. Clocks are something we can build and observe. Time is a bit more elusive.

 

So leave it as an elusive concept. My answer to "what is time" is that it is an undefined term. By way of analogy, Euclidean geometry gets along quite nicely even though point, line, and plane are all undefined terms in Euclidean geometry.

[michel123456]

Pretty much everything.

 

It would be rather nice to be able to throw an object into the past. I would use that ability to throw a message to the 2004 version of myself: "Buy Google stock as soon as it goes IPO. Oh, and buy some Apple stock too. Buy as much as you possibly can."

 

 

 

 

The past is a very wide place.

You can go into the past but not into your own past. You can go into someone else's past: go to the Moon and you will be into the rest of the world's approx 3seconds past. If you go to a planet a light-year away, you will be a year ago in all-the-others-past. Of course the travel will take say a thousand years: leaving today, you will reach the planet in year 3012, the landing scene will be observed on Earth in year 3013. You will be 1 year in Earth's past.

 

But if you want to go in year 2004 here on Earth, I am afraid that's impossible: time and place do not allow that kind of combination.

 

Because you are still seeing the object after you threw it. You are not throwing into the past.

Again; when an object is distant from you, don't you see it "as it was in the past"? The electromagnetic force, the gravitational force you measure, aren't they from the object "as it was in the past"?

 

If I throw a ball at you will it hit you before I throw it or after?

 

 

But the spaceship will not land before it left Earth.

 

The ball will hit after, and the spaceship will not land before it left Earth. To do that the ball and spaceship should have traveled faster than SOL and that is physically impossible.

[DrRocket]

It has been my experience that discussions of "past" really muck up the works, physics-wise. What SR quantifies are things like time intervals and rates.

 

SR also makes precise the notions of a past light cone and a future light cone. The Lorentz transformations used in physics are those linear transformations that preserve the Minkowski metric (i.e. preserve the spacetime interval) and that also preserve the past and future light cones (so called orthochronic Lorentz transformations).

 

I think it reasonable to say the the past of an observer is the past light cone of that observer.

 

But if the discussion turns toward philosophy this nice tidy mathematical construction does indeed get all mucked up.

 

Not that you care about rep points, but +1 for that.

 

 

You are right, I don't much care. I find that rep points are inversely related to the technical content of a post, and this is not really an exception.

 

Yes "Time is what clocks measure". That is the best that we can do, but it is not entirely satisfactory. Maybe someday there will be an answer with deeper insight, but I have no idea what that answer might be.

[Spyman]

The ball will hit after, and the spaceship will not land before it left Earth.

If I throw a ball at you and it hits you after I throwed it, then clearly from my vantage point when I let the ball go, it hits you in the future.

 

If the spaceships arrives thousand years after it left Earth, then it will land in the future from our view right now when it takes off.

 

Saying that I am throwing the ball into the past or that the spaceship is moving into the past makes people think that you intend to mean that the objects are travelling in the opposite direction as the arrow of time. You need to be careful to express yourself with clarity and use the words like everyone else commonly will interpret them or the discussion will very fast get confusing and degenerate.

 

When I read what you wrote here to D H for instance, I get very confused of what you try to say:

 

You can go into the past but not into your own past. You can go into someone else's past: go to the Moon and you will be into the rest of the world's approx 3seconds past.

You can NOT go into anyones past, you are not able to go into my past and prevent me from making this post or send a message to influence it.

 

But then later you say:

 

But if you want to go in year 2004 here on Earth, I am afraid that's impossible: time and place do not allow that kind of combination.

So you seem to understand that you can't go into the past, neither your own or someone elses, but yet you choose to express yourself contradictory which implies that there is still something that you are perceiving differently or fail to voice.

 

An astronaut standing on the Moon is not in our past, it is only the image of him that will be a pair of seconds old when it reaches us. If you are seeing something distant from you then you are looking at history, "as it was in the past", but that doesn't mean that the objects you see are in your past, we can't see them instantly as they are in our now, but if they are not in our now then we would stop seeing them in the future. If the astronaut would not be standing there on the Moon and waving his arms, right now when you see the old image of him looking down at you, then you would not be able to see him wave to you at exactly that time interval later on that the speed of light causes over that distance.

Edited March 6, 2012 by Spyman

[michel123456]

I apologize if I am confusing you and the other members here.

But

If you accept that a galaxy 3 billion years away from us is a galaxy in our past, fully, physically, because of the max speed of all physical interaction, then you must also accept that any object that is distant from you is in your past, even it is a very very close past of not even a nanosecond. Distance means time: you cannot observe anything at a distance without time.

Which means that ONLY THE PAST IS OBSERVABLE.

 

You should also consider that the future is not observable.

So you cannot send anything in the future and observe it.

You cannot observe anything coming from the future, be it a ball or a spaceship. When the ball comes to me , it comes from someone who sent it some time before, in my past.

Similarly:

When we send something away, be it a ball or a spaceship, we always send it to the past. There is no other physical way.

[Tres Juicy]

I apologize if I am confusing you and the other members here.

But

If you accept that a galaxy 3 billion years away from us is a galaxy in our past, fully, physically, because of the max speed of all physical interaction, then you must also accept that any object that is distant from you is in your past, even it is a very very close past of not even a nanosecond. Distance means time: you cannot observe anything at a distance without time.

Which means that ONLY THE PAST IS OBSERVABLE.

 

You should also consider that the future is not observable.

So you cannot send anything in the future and observe it.

You cannot observe anything coming from the future, be it a ball or a spaceship. When the ball comes to me , it comes from someone who sent it some time before, in my past.

Similarly:

When we send something away, be it a ball or a spaceship, we always send it to the past. There is no other physical way.

 

"Observing" and "going to" are two different things entirely

 

We can only observe the past due to the speed of light but that does not mean that we move into the past as we move away from an observer, only that the light travelling between us has finite speed

[Spyman]

I apologize if I am confusing you and the other members here.

No apology needed, at least not for me anyway.

 

 

If you accept that a galaxy 3 billion years away from us is a galaxy in our past, fully, physically, because of the max speed of all physical interaction, then you must also accept that any object that is distant from you is in your past, even it is a very very close past of not even a nanosecond. Distance means time: you cannot observe anything at a distance without time.

Which means that ONLY THE PAST IS OBSERVABLE.

No, I don't accept this, the photons arrive to us from an event in the past and carry information therefrom, but the galaxy has now moved to a different location and aged since then. Anything we see is only an IMAGE of something as it was in the past, not where it is right now.

 

Further more the close future is observable if I have time to wait until it becomes my past. As such I can make predictions of where an object is physically right now and later when this event is in my past and is observable confirm if it actually was where I thought it was when I made the prediction.

 

 

You should also consider that the future is not observable.

So you cannot send anything in the future and observe it.

You cannot observe anything coming from the future, be it a ball or a spaceship. When the ball comes to me , it comes from someone who sent it some time before, in my past.

I can throw a ball in your direction and predict that it will hit you in a future moment, later on the ball hits you at the predicted time and slightly afterwards I can confirm that the ball did hit you as I predicted.

 

If you throw the ball towards a wall making it bounce back so you can catch it again, then it will always be you in the past who throws the ball to you who catches it in the future. You are NOT able to send the ball back to the past, so that you catch it from the future.

 

 

When we send something away, be it a ball or a spaceship, we always send it to the past. There is no other physical way.

IMO: "send it to the past" equals "backwards in time" which means the opposite direction as the arrow of time.

 

If you really think this then you are very very wrong and if you don't then communication has failed.

[michel123456]

(...)communication has failed.

[zapatos]

I apologize if I am confusing you and the other members here.

But

If you accept that a galaxy 3 billion years away from us is a galaxy in our past, fully, physically, because of the max speed of all physical interaction, then you must also accept that any object that is distant from you is in your past, even it is a very very close past of not even a nanosecond. Distance means time: you cannot observe anything at a distance without time.

Which means that ONLY THE PAST IS OBSERVABLE.

 

You should also consider that the future is not observable.

So you cannot send anything in the future and observe it.

You cannot observe anything coming from the future, be it a ball or a spaceship. When the ball comes to me , it comes from someone who sent it some time before, in my past.

Similarly:

When we send something away, be it a ball or a spaceship, we always send it to the past. There is no other physical way.

I don't. This is clearly the problem.

[michel123456]

I never said backwards in time.

 

Again: (quoting myself)

7. we know that information needs time to travel, it's an extension of point 1 of the OP. As a direct consequence we know that any observation is observation of the past.

 

Maybe that's the point of misunderstanding?

[zapatos]

I never said backwards in time.

 

Again: (quoting myself)

 

 

Maybe that's the point of misunderstanding?

But you did say:

 

9. so we know that if you take a close object, then propulse it far away, you are throwing the object into the past (and not in the future as comonly believed). And that is coherent with point 8. because the object is continuously observable along its path. As the distance increases the object falls into the past.

 

Perhaps you can explain the difference between 'backwards in time' and 'into the past'.

[michel123456]

But you did say:

 

 

 

Perhaps you can explain the difference between 'backwards in time' and 'into the past'.

O.K.

"into the past" is everything we observe around us. The Observable Universe is into the past. The Andromeda Galaxy is into the past. The Sun is into the past. Your computer screen is into the past.

 

Backwards in time means turning back the arrow of time. It is a completely different concept.

[Tres Juicy]

O.K.

"into the past" is everything we observe around us. The Observable Universe is into the past. The Andromeda Galaxy is into the past. The Sun is into the past. Your computer screen is into the past.

 

Backwards in time means turning back the arrow of time. It is a completely different concept.

 

 

This is clearly wrong. You are confusing distance with "the past"

[zapatos]

O.K.

"into the past" is everything we observe around us. The Observable Universe is into the past. The Andromeda Galaxy is into the past. The Sun is into the past. Your computer screen is into the past.

 

Backwards in time means turning back the arrow of time. It is a completely different concept.

I think the problem is that you are using 'into the past' differently than everyone else uses it. If I tell one person (other than you) that I am going to travel 'into the past', and I tell another person that I am going to travel 'back in time', they will both take that to mean the same thing.

 

As far as I can tell, when you say 'into the past', you mean what everyone else would call 'in the distance'.

 

One of the problems is that you sound as if distance and time are the same thing. For example, if something is one light day away, then information about that thing is one day in the past. But if my wife wrote me a note and I am not allowed to open it until tomorrow, then the information in that note is also traveling one day into the past, even though it is not physically moving away from me. I still don't get why you are using terms that can be so confusing. Why not just say that when you throw something away from you it is moving to a place where information from that things takes longer to get to you?

 

I think you need another term other than 'past' to describe what you are saying.

[michel123456]

I think the problem is that you are using 'into the past' differently than everyone else uses it. If I tell one person (other than you) that I am going to travel 'into the past', and I tell another person that I am going to travel 'back in time', they will both take that to mean the same thing.

 

As far as I can tell, when you say 'into the past', you mean what everyone else would call 'in the distance'.

 

One of the problems is that you sound as if distance and time are the same thing. For example, if something is one light day away, then information about that thing is one day in the past. But if my wife wrote me a note and I am not allowed to open it until tomorrow, then the information in that note is also traveling one day into the past, even though it is not physically moving away from me. I still don't get why you are using terms that can be so confusing. Why not just say that when you throw something away from you it is moving to a place where information from that things takes longer to get to you?

 

I think you need another term other than 'past' to describe what you are saying.

 

 

The image from the past is the point in space & time we are gravitationaly attracted to. The image is sending us EM radiation, photons and neutrons and all that stuff. The image from the past is what we observe, is what physically counts. When you observe something, it also means you can measure it, by all means. And there is no one thing that you can measure in the present nor in the future. The only thing that is able to access is the past.

 

I am not aware of any other word for the past. In a Minkowski diagram, the past light cone is called the past. I don't understand what is bothering you.

 

And I am not the one who is mixing time with distance, I am not the one who made the universe.

Edited March 6, 2012 by michel123456

[zapatos]

The image from the past is the point in space & time we are gravitationaly attracted to. The image is sending us EM radiation, photons and neutrons and all that stuff. The image from the past is what we observe, is what physically counts. When you observe something, it also means you can measure it, by all means. And there is no one thing that you can measure in the present nor in the future. The only thing that is able to access is the past.

 

I am not aware of any other word for the past. In a Minkowski diagram, the past light cone is called the past. I don't understand what is bothering you.

 

And I am not the one who is mixing time with distance, I am not the one who made the universe.

Perhaps we are just not able to communicate clearly. Why don't you have someone else explain it to me who is not bothered by your statement that as you "propulse it far away, you are throwing the object into the past".

[swansont]

I am not aware of any other word for the past. In a Minkowski diagram, the past light cone is called the past.

 

Then perhaps you should frame your discussion in terms of light cones. You did say you wanted to discuss this in terms of physics.

[zapatos]

And I am not the one who is mixing time with distance, I am not the one who made the universe.

But you are the one who is making them equivalent.

[Tres Juicy]

The image from the past is the point in space & time we are gravitationaly attracted to....

 

Only because gravity cannot propogate faster than light

 

That does not mean it's in the past

[michel123456]

Then perhaps you should frame your discussion in terms of light cones. You did say you wanted to discuss this in terms of physics.

That is an excellent idea.

 

Replacing the word "past" with "Past Light Cone" or PLC.

 

Perhaps we are just not able to communicate clearly. Why don't you have someone else explain it to me who is not bothered by your statement that as you "propulse it far away, you are throwing the object into the past".

 

That is because no-one is used to the concept, not that the concept is wrong.

 

Swansont is right.

 

The statement should be

"When you propulse an object far awayfrom you, you propulse it inside your PLC"

 

Which is trivial, since all observable objects are in your PLC. When you propulse an object it does not dissapear from the observable world. And the fact that the distance to the object increases or decreases pay no role at all.

[Spyman]

(...)communication has failed.

I am not convinced that it is only a language barrier, this reply to zapatos indicates otherwise:

 

Perhaps we are just not able to communicate clearly. Why don't you have someone else explain it to me who is not bothered by your statement that as you "propulse it far away, you are throwing the object into the past".

That is because no-one is used to the concept, not that the concept is wrong.

If no-one is used to your concept then it is NOT in line with scientific consensus.

 

If your concept is in line with consensus then your wording and explanations don't suffice.

 

 

You act and express yourself as if the real objects actually physically are where you observe them to be, both in space and time.

 

If that is your concept then your concept is clearly wrong, if that is not your concept then your expressions thereof are wrong.

 

 

We now have three pages of discussion and I still don't know if it is only a bad wording or a very strange concept...

[michel123456]

If your concept is in line with consensus then your wording and explanations don't suffice.

My concept is in line with scientific consensus, it may not be in line with common thinking.

 

You act and express yourself as if the real objects actually physically are where you observe them to be, both in space and time.

It depends on what you mean with the word "physically". In a spacetime diagram (following scientific consensus) a point is an event and an object is a line. So I understand (please correct me) that an object "physically" exist all along the line. If that concept is wrong, please tell me.

 

If that is your concept then your concept is clearly wrong, if that is not your concept then your expressions thereof are wrong.

I surely encounter difficulties to express myself. And maybe I am wrong.

 

We now have three pages of discussion and I still don't know if it is only a bad wording or a very strange concept...

IMHO the strange concept is to believe that we can send something to the future. I don't think it is so complicated to understand that all that we are observing belong to the past. It is the basic configuration of a Minkowski diagram: the summit of the light-cone is at the observer, the entire observable universe is in the past. Any object located at a distance in present time is outside the observable universe. There is no ambiguity: the present is not observable, nor the future.

 

Now, if you believe that what we are observing belongs to the present then you should explain that.

Edited March 7, 2012 by michel123456