what we know about Time

[MigL]

Well Owl, let me try to explain along the same lines as the other posts on this topic.

Your 'now' is the apex of a past light cone which extends doownward into the two bottom quadrants of a distance time graph. The slopes of the light cone are +/-186000 where the distance is in miles and the time is in seconds.

At your 'now', the apx of the cone, the sun is outside your observable universe and will not enter it until the light cone passes through the distance of 93000000 miles which is in about 8 min.

I don't know what being outside the observable universe means to you, but that sun will never have any effect on us in any way. We can only ever perceive the sun of 8 min ago.

Oh, and don't let DrR catch you voicing your 'universal now' philosophy, or he'll be all over you again.

Edited March 13, 2012 by MigL

[owl]

Well Owl, let me try to explain along the same lines as the other posts on this topic.

Your 'now' is the apex of a past light cone which extends doownward into the two bottom quadrants of a distance time graph. The slopes of the light cone are +/-186000 where the distance is in miles and the time is in seconds.

At your 'now', the apx of the cone, the sun is outside your observable universe and will not enter it until the light cone passes through the distance of 93000000 miles which is in about 8 min.

I don't know what being outside the observable universe means to you, but that sun will never have any effect on us in any way. We can only ever perceive the sun of 8 min ago.

Oh, and don't let DrR catch you voicing your 'universal now' philosophy, or he'll be all over you again.

 

I understand the light cone model.

It is only a model. Probably works very well as a conceptual framework for relativity theory and its very successful math.

 

"My now" is not "the apex of a light cone extending downward into the two bottom quadrants of a distance time graph."

 

That is your relativity model of "my now" which is only a metaphorical and conceptual model. When you get into the "slopes of the light cone" your are really taking the model too seriously.

The sun is never "outside my observable universe." It simply takes 8 min. for its sunlight to reach me and be observed.

Then you say it:

"...(it) will not enter it until the light cone passes through the distance of 93000000 miles which is in about 8 min."

 

Repeat: The cone is only a metaphorical model. Its distance is 93 million miles. That's 8+ light minutes away. It is shining all the time. I see it as it was 8 min. ago. It's not that complicated.

You say:

"I don't know what being outside the observable universe means to you, but that sun will never have any effect on us in any way."

 

"That sun?" It is never outside the observable universe. It just takes 8 min to see what IS GOING ON there.

 

I got a chuckle out of your,

"Oh, and don't let DrR catch you voicing your 'universal now' philosophy, or he'll be all over you again."

 

Thanks for the warning. It really scares me.

 

He never did respond to the "global now" reference gave him ( cosmology beyond the local scope of relativity.)

 

Maybe I'll look it up and re-post later.

 

Its very simple. "It is now" here on earth and there on the sun, and however far away. The distance requires a delay in all cases between "what is happening" out there and when we see it. Not an infinite number "nows" for all possible loci in the universe... just travel time for info to reach across space.

[michel123456]

I understand the light cone model.

It is only a model. Probably works very well as a conceptual framework for relativity theory and its very successful math.

(...)

 

For the sake of this thread, and finally, that is not of so much importance. Your horizontal "now" is another model not so different from the triangular one.

see the followings 1 2 3 scenarios:

 

As you can see, the difference is not so fundamental. The whole discussion is about the slope of the present line (the simultaneity line). For Owl, the slope is null, the angle is zero. For someone like me, the slope is not null because one has to take into account the Speed Of Light which is not only an observational phenomena, it is a very deep profound fundamental inescapable physical phenomena. The value of the slope (between scenario 2 & 3) is only a matter of units on the graph. By convention the scenario 3 is the correct one.

 

IMHO what is important, and what remains unclear, is what about the whole rest of the Universe, the enormous blank part of the sheet of paper, the part that we cannot observe directly.

 

Iggy thinks that everything persist in time. I understand that for him, the non-observable part is filled with past and future objects. The Block Universe?

In this universe, where is mass?

Is there a 'hypermass" that is the product of "instant mass" (that we observe) by time?

Or is there only one mass (that we observe) sliding in time?

 

What is the official scientific version?

Edited March 14, 2012 by michel123456

[Iggy]

Following Iggy's interpretation, Michel is not at any point of the diagram, Michel is a line (a curve) on the diagram because Michel "persist" in time.

It isn't my interpretation. It is how space time works.

 

The definition of "object" coincides with the definition of "world line" in space time.

 

You can't directly observe the Hiroshima atomic blast of 1945. That event is not directly observable at this time. The object, Japan, had mass and existed in 1945. If you keep separate the idea of an event (the dots on the diagram) and the idea of an object (the lines on the diagram) then there should be no issue

 

Iggy thinks that everything persist in time.

Except with my car keys, I do generally think conservation laws work and things don't macroscopically pop in and out of existence.

 

I understand that for him, the non-observable part is filled with past and future objects.

past and future events. This has got to be the issue. Objects are not discontinuous in the dime direction in space time. It seems like you've convinced yourself they are, but that won't work.

[michel123456]

It isn't my interpretation. It is how space time works.

 

The definition of "object" coincides with the definition of "world line" in space time.

 

You can't directly observe the Hiroshima atomic blast of 1945. That event is not directly observable at this time. The object, Japan, had mass and existed in 1945. If you keep separate the idea of an event (the dots on the diagram) and the idea of an object (the lines on the diagram) then there should be no issue

 

 

Except with my car keys, I do generally think conservation laws work and things don't macroscopically pop in and out of existence.

 

 

past and future events. This has got to be the issue. Objects are not discontinuous in the dime direction in space time. It seems like you've convinced yourself they are, but that won't work.

 

Then again, where is mass?

 

An event has mass?

[Iggy]

Then again, where is mass?

with the object

 

An event has mass?

Objects have mass. Events are... the 5th dot down -- the indented one: http://fr.wikipedia.org/wiki/%C3%89v%C3%A9nement

[michel123456]

with the object

 

 

Objects have mass. Events are... the 5th dot down -- the indented one: http://fr.wikipedia.org/wiki/%C3%89v%C3%A9nement

 

Right: objects have mass.

and you said the object is a line on the diagram.

So I understand that your POV is that mass is distributed along the line on the graph. So that mass in this diagram is represented as a surface perpendicular to the sheet of paper. Is that correct?

Edited March 14, 2012 by michel123456

[Iggy]

Right: objects have mass.

and you said the object is a line on the diagram.

So I understand that your POV is that mass is distributed along the line on the graph. So that mass in this diagram is represented as a surface perpendicular to the sheet of paper. Is that correct?

Yes, in classical physics it would be a surface orthogonal to space and time along the world-line. As spyman pointed out, in relativity is warps the space-time around and along the world-line.

 

When do you think particles have mass?

[owl]

For the sake of this thread, and finally, that is not of so much importance. Your horizontal "now" is another model not so different from the triangular one.

In keeping with the thread title, "what we know about time" is not limited to graphs and models. What I know about time is not your "horizontal model" of "now."

In the English language, "now" means "the present," and space (specifically its linear component, distance) does not make "the present" different in each and every "place" in space. It only means that information about "the present" now happening elsewhere will take time to reach us.

[michel123456]

Yes, in classical physics it would be a surface orthogonal to space and time along the world-line. As spyman pointed out, in relativity is warps the space-time around and along the world-line.

 

When do you think particles have mass?

 

Hmmm. So for an object at rest mass should be a surface of length=time and height=????

 

And how do you manage to measure the mass of an object? Do you measure from the Big Bang until the end of times?

 

Oh, and I guess you believe also that mass increases with time, since you believe mass is a surface along the world line.

Edited March 14, 2012 by michel123456

[Spyman]

The problem here is that you cannot reach simultaneity at the end, neither at the beginning, because there exist distance between Michel and Spyman.

I agree that Michel in the middle does not win this race against Spyman at the outermost right. The race never stops, Michel cannot observe anybody exactly on his line, he can only observe the ones that are upon the triangle. If there were a lost soldier 2 steps behind, or another 2 steps in front, it would be physically impossible for Michel to observe him directly.

Reread the content, the accuracy is more than adequate to determine if said markers is placed in one straight line or in a "migrating birds" formation.

 

 

I don't fully understand your explanation but yes, the box will reach you in a time after the throw event. There is no motion backwards in time.

If it will reach the destination after the journey started, then it is said to be moving forward in time, simple as that.

 

 

Again, this is tricky because the diagram is made by an external observator that does not exist. I am Michel and i observe you constantly in my past. You are Spyman and you observe me constantly in your past. The external observator may draw a diagram with a present line in which the clocks are ticking together, but that does not mean that we "are" physically there. Following Iggy's interpretation, Michel is not at any point of the diagram, Michel is a line (a curve) on the diagram because Michel "persist" in time.

There is no need for an external observator, I can bounce a ball against a wall, the event when the ball hits the wall must be sometime along it's worldline, between the two events when I throw it and catch it again. Since both I and the ball persist along our worldlines during this time interval, the event when the ball bounced against the wall must have coexisted with an event when I was looking at it.

 

If the worldline Michel is causing an event at time 3 and the worldline Spyman is causing an event at time 3, then for all intents an purposes those two events did happen at time 3, which means that Michel and Spyman where both there at the same time causing these events. At the event where Spyman looks at his clock and determines that it is time 3 in his present, he knows¹ that Michel is in this present somewhere too, because Michel can't stop existing.

(¹ This knowledge is based on the assumtion that current verifyed laws of nature is correct and continues as usual for this period of time.)

 

You need to define what physically there "are", if my clock is beeping at time 3 then am I physically there or not? If the requirement is that I am observable, then clearly I am not there for Michel at time 3. But if the requirement is that I cause an event at time 3 then I am there.

 

 

You mean that Michel can use the laws of physics and calculate when Spyman waves his arms and after a headache get the expected result that he waved his hands at the expected time. Yes.

The "expected result" means that Michel can CONFIRM if Spyman really was causing events in his past present or not.

 

If Michel carefully examines the laws of physics without an headache he might understand that Spyman is unable² to leave Michel's present.

(² Spyman don't have the means necessary to hide inside the event horizon of a black hole nor to travel beyond Michel's cosmic event horizon.)

 

 

Q.Where was the event when your clock beeped?

A. Here (for me)

Q.where was the event when mine clock beeped?

A. somewhere far away (for me) and here (for you)

LOL - They both are clearly on the line we call present in the diagram.

 

 

Intuitively, we were both on the horizontal line you call the present. But neither you or me could observe that.

 

I say intuitively because Michel & Spyman seem discussing about objects "moving" in time. They were here, then there. If they are there, they are not here: it is motion. They are not everywhere.

The event when Spyman's clock beeps happens at the same time as the event when Michel's clocks beep, those two events are on the same horizontal line we once called the present, they both happened simultaneously, they both shared the same time coordinate, they where both there at that time.

 

We can't observe directly at present time that we are both there, but afterwards we can confirm that we in fact was there. If we always confirm that the objects we observe continued to exists at the time that was the former present time, then we get increasingly more certain that all objects³ will always continue to exists in our present time. AFAIK the conservation of mass-energy law have NEVER been shown to be violated.

(³ Depending on what can be described as an object, the object might get destroyed, but it's parts or mass-energy doesn't vanish without a trace.)

 

If two objects worldlines proceed, (in parallel), through each others past and future light cones, then they must also coexist in their present. Moving said objects apart or closer together doesn't change that.

[Iggy]

Hmmm. So for an object at rest mass should be a surface of length=time and height=????

No, mass doesn't increase with time. We don't get a new sun every day adding mass to the old one. Each dot on the diagram is an event -- not an object. Each new event does not imply new mass. Mass is not a property of events.

 

And how do you manage to measure the mass of an object?

There are two methods for measuring mass. You can apply a force to the object and measure the acceleration. On a space-time diagram this involves dividing a known force applied to the object by the change in the slope of the wolrld-line after the force is applied. You can also measure it with a scale if you know the gravitational acceleration.

 

On a space-time-mass diagram you can just look at the height in the mass dimension.

 

Oh, and I guess you believe also that mass increases with time, since you believe mass is a surface along the world line.

It is not a matter of belief.

 

Imagine a rectangle. It takes two dimensions to show. Do we say that the height changes because the rectangle makes a surface? Each point along the width of the rectangle is not a new and different rectangle adding to its height. Each point along a world-line is not a new and different object adding to its mass.

[michel123456]

(...) Each point along a world-line is not a new and different object adding to its mass.

 

Agree.

But I thought you have said that an object is a line, not a point. Now you say that only a point on the line has mass (on which I agree). Your thoughts are not coherent: either the object is a line and thus the whole line has mass, either the the object is the point in which case the point has mass (It is the correct answer IMHO).

[Iggy]

But I thought you have said that an object is a line, not a point.

That is correct

 

Now you say that only a point on the line has mass (on which I agree).

That isn't what I said. You're not understanding.

 

What point on the width of a rectangle has height? Does "the rectangle" have height, or does "only one single point along the with of the rectangle" have height?

Edited March 15, 2012 by Iggy

[michel123456]

That is correct

 

 

That isn't what I said. You're not understanding.

 

What point on the width of a rectangle has height? Does "the rectangle" have height, or does "only one single point along the with of the rectangle" have height?

 

all the points have height. and the surface of a rectangle has units base (meters) by height (meters) = square meters.

 

If you say that one point has mass (height) then the rectangle has units mass by time (kg.s) which is not units of mass. In this case the rectangle does not represent mass and thus the base line is not an object.

Edited March 15, 2012 by michel123456

[Iggy]

all the points have height.

how do you find the height of the rectangle?

 

In this case the rectangle does not represent mass and thus the base line is not an object.

We already agreed that an object (a point object to be specific) makes a surface on a space-time-mass diagram. You find the mass of the object on the diagram the same way you find the height of the rectangle.

 

How do you find the height of a rectangle?

[michel123456]

how do you find the height of the rectangle?

 

 

We already agreed that an object (a point object to be specific) makes a surface on a space-time-mass diagram. You find the mass of the object on the diagram the same way you find the height of the rectangle.

 

How do you find the height of a rectangle?

 

Oh, now you agree that an object is a point on the diagram. So far you have argued that an object is a line and that a point is an event.

Right from the beginning I have assumed that a point is an object on this diagram and you have argued that I am confusing event with object.

 

And yes, a point-object makes a surface on this diagram. The height represents the mass of the point-object. The rectangle represents the mass of the point-object travelling in time.

[Iggy]

no, a point particle is one that takes up no volume in space. It makes a line in space-time.

 

How do you find the height of a rectangle?

[michel123456]

no, a point particle is one that takes up no volume in space. It makes a line in space-time.

 

How do you find the height of a rectangle?

Iggy, with all my respect, I feel as if you don't want to understand my point.

 

Yes a point particle does not take space, that is the reason why it is not extended to the left or right in the diagram. Nobody is talking about volume yet.

When you say "it makes a line in space-time", I ask you "where is the mass of this point particle" and you answer bizarrely.

 

There are only 2 solutions:

 

1. The object is the line. Since mass is associated with the object, mass is distributed all along the line. In this case mass is the surface of the rectangle and the height of the rectangle is mass/time expressed in kg/s

 

2. The object is a point (what you called yourself a point particle). Since mass is associated with the object, mass is located where the point particle is located. In this case the height of the rectangle is mass (expressed in kg) and the surface of the rectangle is the product of mass by time (expressed in kg.s).

 

 

There is no doubt that point 1 is wrong.

 

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

When you say

It makes a line in space-time.

 

I would say "its trajectory in space-time is a line".

Edited March 16, 2012 by michel123456

[Iggy]

Iggy, with all my respect, I feel as if you don't want to understand my point.

I understand you perfectly. You are expressing yourself well and I get exactly where you're coming from.

 

2. The object is a point (what you called yourself a point particle).

A point in space. Not a point in space-time. The reason I said point particle was to be clear we would have a surface in the mass dimension and not a volume... if you look back at the post you'll see that was my line of thought.

 

There is no doubt that point 1 is wrong.

How then do you find the height of a rectangle? This is the fourth time I've asked. Please.

Edited March 16, 2012 by Iggy

[michel123456]

A point in space. Not a point in space-time. The reason I said point particle was to be clear we would have a surface in the mass dimension and not a volume... if you look back at the post you'll see that was my line of thought.

 

 

What are the units of "a surface in the mass dimension"?

IMHO it should be "a surface in the mass-time dimension" for a point-particle at rest.

 

How then do you find the height of a rectangle? This is the fourth time I've asked. Please.

 

I wonder what kind of answer you are waiting for. In our case, the height is one side of the rectangle, you can "find" it by dividing the surface by the base but I think the height is a given (mass) and the surface of the rectangle is the result.

Edited March 16, 2012 by michel123456

[Iggy]

I wonder what kind of answer you are waiting for.

straightforward. i'm not trying to trick you.

 

You pick up a rectangle. How do you find its height?

 

I don't think you would measure both sides and divide their product.

Edited March 16, 2012 by Iggy

[michel123456]

Measuring?

[Iggy]

Measuring?

assuming you mean to measure from the base to the top,

 

all the points have height.

which point (or points) do I measure to find the height of the rectangle? Remember, we want to height of the whole rectangle... not just the height of one point.

Edited March 16, 2012 by Iggy

[michel123456]

assuming you mean to measure from the base to the top,

That reminds me a very old joke.

 

 

which point (or points) do I measure to find the height of the rectangle? Remember, we want to height of the whole rectangle... not just the height of one point.

???

We know that the rectangle is a rectangle, mass does not vary over time. The height at one point is sufficient.