Suppose that I am looking in my telescope to a distant star

[Delbert]

 

Whoa! Hold on there. Light is theoretically, and as far as can be determined by experiment, massless and therefore travels at the speed of light.

I said to my understanding, If you say it doesn't then it doesn't. I just added that to my comments about propagation speed or the need for a propagation speed.

 

But as for your claim that it's massless, from a purely theoretical position it seems a bold statement to make. Because it says that it can't have any mass whatsoever: like not even 1 preceded by ten million noughts of a gram - or any other greater number of noughts. I'd have thought it's better to say: zero mass as far as we can tell with current technology.

[Strange]

 

There is nothing there , actually there.

 

Well, there is energy, momentum, angular momentum, frequency, ...

 

But whether those things are "real" and whether photons "exist" depends largely on what the words "real" and "exist" mean (more than it does the word "photon"). And that is really just a philosophical point, of no real relevance to science.

[michel123456]

At any instant the object is at a single point in time. I'm not sure how your head can be at a different time than your feet.

Because there is a distance between your head and your feet.

Thank you, thank you.

 

But I think we can all agree that at any instant it is not extended in time.

No, I disagree. If an object is extended in space it must obligatory extend in time. ONLY a point particle could be considered as not extending in time.

[Strange]

Because there is a distance between your head and your feet.

 

That means they are at different point in space, not time.

[michel123456]

"At any instant the object is at a single point in time"

Very profound Strange !

 

But at another instant, it is at another point in time ( +space )

If you were at location A one hour ago, the fact that you are at position B now does not mean you were no longer at position A one hour ago. Points ( events ) in space-time are fixed. GR being classical, past and future are just as 'real' as present. They just can't be accessed like spatial co-ordinates can.

 

Is it just me, or is English ( or any other language ) unsuited for describing the 'workings' of time ?

Motion. It just as if you wanted to explain motion. When an object is here, it is not there. It goes from here to there. It changes coordinate. Why is it so difficult conceptualize the same thing for time?

 

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

When an object moves in space it does not duplicate.

The same concept should apply for time.

 

And it is not metaphysics.

Edited November 26, 2014 by michel123456

[elfmotat]

I said to my understanding, If you say it doesn't then it doesn't. I just added that to my comments about propagation speed or the need for a propagation speed.

 

But as for your claim that it's massless, from a purely theoretical position it seems a bold statement to make. Because it says that it can't have any mass whatsoever: like not even 1 preceded by ten million noughts of a gram - or any other greater number of noughts. I'd have thought it's better to say: zero mass as far as we can tell with current technology.

 

Zero is a nice number. Slightly more than zero is not nice, and generally requires some kind of fine tuning. (This is why the slightly non-zero cosmological constant is so puzzling.) From a theoretical perspective massless photons are much nicer.

[michel123456]

That means they are at different point in space, not time.

And what is the relation between space and time?

Following the learnings of Relativity?

[Strange]

When an object moves in space it does not duplicate.

The same concept should apply for time.

 

The same is true for time. An object can be extended in space and it can be extended in time.

 

You are extended through time for as long as you exist. You are extended in space for as long as you are ... long.

The last two diagrams show a little snapshot of a short period of your life. In the first you are standing still so your spatial position doesn't change. In the last one your position changes uniformly over time.

Your head and feet are always at the same time.

And what is the relation between space and time?

Following the learnings of Relativity?

 

They are observer dependent.

[swansont]

When an object moves in space it does not duplicate.

The same concept should apply for time.

 

 

I'm failing to see where anyone has claimed that the object duplicates. Could you point it out?

[MigL]

" It goes from here to there. It changes coordinate. Why is it so difficult conceptualize the same thing for time?"

Because an object cannot be at two different places, here and there, at the same time.

But that same object can certainly be in the same place at two different times.

 

Maybe you hadn't noticed, but time is different from position, conceptually as well as how it's treated.

You cannot go freely from 'here' to 'there' in the time dimension !

 

I do see where you get the idea of an 'extension in time' though.

Since light takes a finite time to get from your head to your feet, by necessity, the local 'now' at your head must be different from the local 'now' at your feet. This is a minute amount and trivial. GR being a classical theory means it treats all particles as dimensionless points, so although the aggregate 'you' may have a fuzzy ( how long does light take to get from your head to your feet ) , local 'now', the individual particles that make 'you' up all have an explicit local 'now'.

Edited November 27, 2014 by MigL

[swansont]

!

Moderator Note

 

Discussion of photon properties has been split

http://www.scienceforums.net/topic/86677-properties-of-photons-split-from-looking-in-telescope-to-distant-star/

 

[Delbert]

 

That means they are at different point in space, not time.

Space-time according to Einstein.

.

[Strange]

Space-time according to Einstein.

.

 

True. And I suppose another observer might consider your head and feet to be at different times from their frame of reference (although I struggle to come up with a suitable scenario). But from your own frame of reference, your head and feet are both in your that frame and therefore at the same time. (I think!)

[swansont]

If one follows the Einstein clock synchronization protocol, all time in a single inertial frame is the same, i.e. you account for the L/c difference when setting the clock. You could, of course, define a different synchronization protocol, as long as you were willing to rework relativity to account for all of the implications of it.

[michel123456]

I do see where you get the idea of an 'extension in time' though.

Since light takes a finite time to get from your head to your feet, by necessity, the local 'now' at your head must be different from the local 'now' at your feet. This is a minute amount and trivial. GR being a classical theory means it treats all particles as dimensionless points, so although the aggregate 'you' may have a fuzzy ( how long does light take to get from your head to your feet ) , local 'now', the individual particles that make 'you' up all have an explicit local 'now'.

Exactly.

 

The same is true for time. An object can be extended in space and it can be extended in time.

 

1D. You wrote 1D

 

Time is 1D

 

 

You are extended through time for as long as you exist. You are extended in space for as long as you are ... long.

The last two diagrams show a little snapshot of a short period of your life. In the first you are standing still so your spatial position doesn't change. In the last one your position changes uniformly over time.

Your head and feet are always at the same time.

They are observer dependent.

In a spacetime diagram, the events that you observe as simultanate are along the diagonal. IOW simultaneity between your head and your feet is something that spreads through time.It does not mean that head and feet are at the same time. It is physically impossible to observe what is at the same time because all informations travel at velocity equal or less than C.

 

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

 

I'm failing to see where anyone has claimed that the object duplicates. Could you point it out?

Here, if I understand correctly ACG52's comment

 

The fact that the Earth exists at T=0 does not preclude it from existing at other points of the T continuum.

And here from MigL

 

Pzkpfw's cat is at the BBQ at 1pm and will always be there. That point is 'fixed' in space-time.

Pzkpfw's cat is at the Birdbath at 2pm and will always be there. That point is also 'fixed' in space-time.

Space-time events do not move, they are fixed. There is nowhere/nowhen else for them to move to.

The cat follows a world line along the time axis. Actually more of a cat shaped world 'tube'.

We've had this discussion before Michel123456. This is what GR tells us.

 

I'm guessing it wasn't to your satisfaction

Edited November 27, 2014 by michel123456

[Strange]

 

1D. You wrote 1D

 

Time is 1D

 

I meant, "This is you in 1 spatial dimension". Sorry if that wasn't clear.

[swansont]

 

Here, if I understand correctly ACG52's comment

 

 

And here from MigL

 

 

No claims of duplication. Both are saying that the same object continues to exist, so it's present at different times.

[michel123456]

No claims of duplication. Both are saying that the same object continues to exist, so it's present at different times.

How many "you" do you see in this diagram?

 

 

I see at least two. in fact an infinity of "yous" in the interval.

 

The diagram gives the impression that there is a "you' at all time stamps, that all coordinates x,t are inexorably occupied by "you".

It is a completely different concept from motion.

I believe it is wrong.

IMHO the diagram describes a path.

[Strange]

How many "you" do you see in this diagram?

 

One.

 

I see at least two. in fact an infinity of "yous" in the interval.

 

Really? Do you see an infinity of yous in the spatial dimension as well?

 

 

The diagram gives the impression that there is a "you' at all time stamps

 

It is intended to show that you have extent in the temporal dimension in the same way you have extent in the spatial dimensions.

 

Not "a" you at all times, but simply you at all times.

 

 

I believe it is wrong.

 

*shrug*

[michel123456]

One.

Then you are obtuse.

I am afraid you are blinded by your convictions.

 

I'll try otherwise:

 

How many circles do you see in the drawing?

[Strange]

How many circles do you see in the drawing?

 

You are taking my crude, 30 second sketch too literally. There is one circle (your head) which exists across time (in the same way it exists across space).

[michel123456]

You are taking my crude, 30 second sketch too literally. There is one circle (your head) which exists across time (in the same way it exists across space).

What I see is this:

I see 2 circles representing your head.

The one was in the past, the other is in the present. Both represent the same object as time passes by.

 

Can we agree on this?

[Strange]

Can we agree on this?

 

No.

 

What I see is this:

I see 2 circles representing your head.

 

FORGET the circles. It is a 1D representation therefore circles cannot exist. They were just a little joke based on your comment about heads and feet. They don't exist and are not relevant to the diagram.

 

The only relevant part of a diagram is a gray quadrilateral. This shows your extent in space and in time.

 

The one was in the past, the other is in the present. Both represent the same object as time passes by.

 

As you cannot time travel (I assume) your head is not at two points in time; it has extent in time for the period of its existence.

[michel123456]

The only relevant part of a diagram is a gray quadrilateral. This shows your extent in space and in time.

No, I believe it shows inaccurately the path of my existence.

I will show here below what I think is more accurate:

 

 

Your extent in time go from your head to your feet. Because there exist some distance. Any material object that is not a point particle should be represented like this.

 

The diagonal slides into time, it moves. The path in time would be represented by a surface. This path in time would be the corresponding representation of a path in space. It is NOT the object itself.

Edited November 29, 2014 by michel123456

[Strange]

I still don't understand why you think your head and feet are at different times. Mine aren't.