S.R. Defining the present

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S.R. Defining the present

Postby ralfcis on May 1st, 2017, 12:08 pm 

I've been having a really tough time trying to determine what S.R. means by "the present." On the face of it, SR has a different present for each participant. The lines of present, or now slices, are parallel to each participant's x-axis. So at t=0 for the "stationary" participant, the now slice is a horizontal line that represents all distance points on that line are set, by relativity's clock syncing, to t=0. For the "moving" participant, the now slices are slanted and parallel to the x'-axis. All the distance points on the line share the same t' (time dilated) time wrt t.

8crel.jpg


Somewhere I read that the above rule falls apart if the distance separation between points on a line is great enough but I think that comes from advanced relativity so I don't really know the explanation.

All the points on a now slice share the same nominal sync'd time but do they really share the same present moment? If you saw 3 supernovae come on simultaneously in the sky, there is no shared present between you or them. Shared presents are never seen in the present due to the delay of light. They can only be reconstructed as they happened in the past.

The following STD shows how 3 truly simultaneous supernovae spaced 1 light year apart would be seen on earth turning on 1 year apart. The earth would have shared that simultaneous present 3 years ago.

c.jpg


In the next post we'll throw relative motion into the mix with distance separation to see how the two together define the present in relativity.
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Re: S.R. Defining the present

Postby BurtJordaan on May 1st, 2017, 4:58 pm 

The only "truly simultaneous" events in physics are those that happen at the same place in space (co-located) and at the same time. The rest are all relative and observer/frame dependent, like is "the present". Otherwise, there is always the Movie and another word for a gift... :)
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Re: S.R. Defining the present

Postby ralfcis on May 2nd, 2017, 5:35 am 

Sure, I guess the only true present, in the present, is for entangled particles whether they are together or separated, but that too is only between the two particles. I'm talking about a calculated present, between two participants that neither of them was aware of, that happened in the past.

Relativity, on the other hand, tries to create an artificial present through clock synchronization. Every clock in a line is set to the same time so, from one end of the line to the other, any relatively stationary event that is clocked at the same time is deemed to be simultaneous even though they're separated. Two lines of relatively moving clocks will not see the same simultaneity of events. I'm saying that's not the same simultaneity I'm trying to find. Things are not simultaneous in the present for a line of clocks no matter what the time says on their faces. I guess there's face time and real time. However, the clock syncing makes it easier to mark and figure out what was a shared present. My end focus is to figure out if two relative frames aging at the same rate is another definition of present.
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Re: S.R. Defining the present

Postby BurtJordaan on May 2nd, 2017, 6:51 am 

Yes, Einstein found the perfect way to define simultaneity and we never again had to look back.

Make sure that you get the terminology straight. The only frames that I know of that age, are door frames and window frames. I also think you must try and get out of the "aging frame of mind". Rather start to use the correct term like elapsed propertime between two events.

Age is in fact very poorly defined, because (sadly) my feet ages slower than my head for two reasons: they are closer to the center of earth and they often move to and fro relative to my head. So the two-way "twin paradox" applies to them often.
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Re: S.R. Defining the present

Postby ralfcis on May 2nd, 2017, 8:38 am 

BurtJordaan wrote:Yes, Einstein found the perfect way to define simultaneity and we never again had to look back.


They didn't have atomic clocks in those days. They didn't even have atoms yet. There are many ways to do timing. It can be synchronous or async or you can depend on the universal accuracy of atomic clocks as the basis of all timing. Then you use light pulses as markers and you just need the accurate duration between them that atomic clocks provide.

Rather start to use the correct term like elapsed propertime between two events.


i.e. aging in the vernacular. Everything ages at the proper time in its own frame and age difference occurs when you compare frames under specific circumstances.
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Re: S.R. Defining the present

Postby BurtJordaan on May 4th, 2017, 6:50 am 

ralfcis » 02 May 2017, 14:38 wrote:They didn't have atomic clocks in those days. They didn't even have atoms yet. There are many ways to do timing.

Yea, but Einstein had light! He obviously did not invent it; someone before him said: "Let there be light".

Light and logic and any clock, that's all he needed to define "now".
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Re: S.R. Defining the present

Postby mitchellmckain on May 5th, 2017, 1:31 am 

ralfcis » May 2nd, 2017, 4:35 am wrote:Relativity, on the other hand, tries to create an artificial present through clock synchronization. Every clock in a line is set to the same time so, from one end of the line to the other, any relatively stationary event that is clocked at the same time is deemed to be simultaneous even though they're separated.

Creating a present is not what this is about. The point is to get beyond our invalid assumptions about simultaneity and thus talk about concrete clocks to see what happens. If you change your velocity in the direction of the clocks then assuming those clocks all still read the same time will lead to contradictions.

The only way to overcome these logical contradictions is get rid of our Euclidean idea of space-time as a series of instantaneous snapshot strung together.

ralfcis » May 2nd, 2017, 4:35 am wrote:Sure, I guess the only true present, in the present, is for entangled particles whether they are together or separated, but that too is only between the two particles. I'm talking about a calculated present, between two participants that neither of them was aware of, that happened in the past.

If everything is categorized into past, present, and future, then the present is everything outside the past and future light cones. It is everything at a space-like distance from you, so if d is the spatial distance then the present includes a time interval of length 2d/c (where c is the speed of light). For example, the present at Saturn is a period of time (on average) which is 22 hours long and at Alpha Centauri the present is a period 8.74 years long. These periods are outside your past and future light cones and thus nothing in those periods of time should be called past or future. And these periods do not change when you change your velocity.

ralfcis » May 2nd, 2017, 4:35 am wrote:Two lines of relatively moving clocks will not see the same simultaneity of events. I'm saying that's not the same simultaneity I'm trying to find. Things are not simultaneous in the present for a line of clocks no matter what the time says on their faces.


In sense you are exactly right...

Let's say you have two ships each with a line of synchronized clocks from front to back and one passes the other at a relativistic speed. Then for each the clocks on their own ship remain synchronized. It is the clocks on the other ship which they conclude are not synchronized. And that is where you are correct to think that this synchronization does not define the present. But the correct conclusion is that the idea of the present as a snapshot in time must be discarded. According to the above explanation, all the clocks in our example are in the present because at a distance the present is a time interval which includes the times they see on the clocks of the other ship (no matter how fast the other ship is going).

ralfcis » May 2nd, 2017, 4:35 am wrote:I guess there's face time and real time.

This is not the solution because remember that for each of the two ships the clocks on their own ship remain synchronized. This is not about clocks not reading the right time. But it is about needing to redefine what is meant by the present. That part is correct.
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Re: S.R. Defining the present

Postby ralfcis on May 8th, 2017, 9:42 am 

Sorry mitchellmckain, can I respond to your post in 5 months. I'm just trying to write down what's in my backlog before I forget it all. Also my threads get shut down if I take too long completing them.
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Re: S.R. Defining the present

Postby ralfcis on May 8th, 2017, 12:10 pm 

There are many pieces to the puzzle of defining the present in relativity. The pieces are:

distance separation
relative velocity
slope of present lines
slope of same age lines
speed of light time marker signal pulses
two participants relation to a common moving or stationary reference frame
relative time dilation coordinate values at line intersections

Yes it's a difficult sleet storm to trudge through especially with the problem of establishing a common terminology of what the above terms mean.

Relativity doesn't condone the idea of a universal present with everyone in the universe sharing the same calculated slice of the present no matter where they are. But in truth, most relative velocities between most participants are far enough away from the speed of light so there is a slightly fuzzy universal present. But we're not talking about that, we're talking about the precise relativistic definition of the present.

I'll have to start that tomorrow in the next post.
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Re: S.R. Defining the present

Postby mitchellmckain on May 8th, 2017, 3:33 pm 

ralfcis » May 8th, 2017, 11:10 am wrote:There are many pieces to the puzzle of defining the present in relativity. The pieces are:

distance separation
relative velocity
slope of present lines
slope of same age lines
speed of light time marker signal pulses
two participants relation to a common moving or stationary reference frame
relative time dilation coordinate values at line intersections

Since the actual present isn't a line, any lines which you have marked as "present" is a mathematical artifice, or at least just one of many lines which are all a part of the actual present. Not sure what is meant by "same age lines." In any case, until you master the relativity of simultaneity you will never understand relativity.

Here is a good example for getting a handle on this. Suppose ship A is traving at 86.6% of the speed of light with respect to B, and his path takes him through a tunnel, where B is waiting, just a little more than half the length of his ship. Lorentz Contraction means A is 1/2 as long in the direction of motion according to B, so B plans to slam down two doors in order to trap A in the tunnel. What happens?

Well according to A the front door slams down first and so either A has to stop or he crashes into the door. Either way, the door behind him only shuts when the tail of his ship passes through it. This means that if A does try to stop that fast it will be as bad as crashing into the door, because neither force nor message can travel to the ends of his ship in order to make all of it stop before that second door slams down.


ralfcis » May 8th, 2017, 11:10 am wrote:Relativity doesn't condone the idea of a universal present with everyone in the universe sharing the same calculated slice of the present no matter where they are.

Correct!

ralfcis » May 8th, 2017, 11:10 am wrote:But in truth, most relative velocities between most participants are far enough away from the speed of light so there is a slightly fuzzy universal present. But we're not talking about that, we're talking about the precise relativistic definition of the present.

Incorrect. The definition of the present has absolutely nothing to do with relative velocities. At least, the definition I gave above is the definition which doesn't change with velocity. That 8.74 period which is the present at Alpha Centauri doesn't change with velocity, and I don't just mean the length doesn't change but the actual period of time, doesn't change, so this definition of the present is invariant under the change of velocity.
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Re: S.R. Defining the present

Postby ralfcis on May 9th, 2017, 11:46 am 

I forgot the most important piece: reciprocity for time dilation, aging, televised aging and present time. But more on this later, for now let's start with the basics.

1cpres.jpg


In this STD there is Bob's stationary vertical axis compared to both a light signal that bounces back to Bob after 4 years and Bob's stationary friend Charlie 5 light years away. The horizontal dotted lines are Bob's present lines extending out into space.

Bob sends out a light pulse at t=0. That point is a very high level 4 present (no such thing as a high level 4 present in relativity but I will show there are different degrees of present so bear with me). Bob is co-located with the light pulse and shares that present, in the present. As soon as you bring in distance separation, the present must be calculated to find out what was the present then, not what is the present now.

Since Charlie is separated from Bob, he shares a level 3 present with him. His shared present with Bob is not shared in the present, it must be calculated 5 years later. This can be done in 2 ways. First, pre-sync Charlie's clock with Bob's network clock which is how relativity does it. Another way is Charlie sends pulses out to Bob with Charlie's clock reading. The time Bob reads from Charlie when Bob has aged 5 years is zeroed much like a stopwatch at the starting gun. Subsequent clock readings from Charlie will have this initial value subtracted from them. The universal independent accuracy of atomic clocks makes this method possible.

When Bob has aged two years, light has traveled 2 years. So light and Bob are traveling through time (aging) at the same rate. Charlie also shares the same aging rate along the same horizontal dotted line. Bob's relationship with light is downgraded to a level 3.5 present. It's no longer co-located with Bob but it's light so we don't really need to verify that it has reached the 2 light year mark in 2 Bob years.

Charlie is not light so he does send a signal back to Bob at the two year mark as a courtesy to verify their clocks are sync'd. The light signal Charlie would send back to Bob would reach him at Bob t=7. It would confirm that the zeroed clock reading for Charlie would show that 5 years ago, both Bob and Charlie had aged 2 years at the same rate of 1 yr/yr. Not only had they aged the same but their clocks have effectively the same time. They have aged the same at the same time; there is no time dilation. The clocks along a dotted line all have the same face time and Charlie's present lines are horizontal and overlap Bob's present lines. None of this will not be true once relative velocity is brought into the picture.

Televised aging rate (which I also forgot to mention as a piece of the puzzle) is represented by the diagonal dashed lines between Bob and Charlie between t=0 and t=1. Bob sees Charlie age 1 yr per Bob year and Charlie will see Bob age 1 yr per Charlie year. The televised signal between them will reciprocally show the images flow at the same rate of time (normal proper rate of time flow) as their own. Once relative velocity comes into play, the reciprocal images will come in slow motion or fast forward depending on the direction of the relative velocity.

It's important to note the televised aging rate is not the same thing as the aging rate. I can only clarify this statement once we get into the discussion of how relative velocity changes things. In this example, the televised aging rate is the same as the actual aging rate of 1yr/yr.

These minutiae all seem incredibly tedious but it sets up how all the puzzle pieces making up the present will begin to diverge from each other once relative velocity is brought into the picture. Once we can account for the divergence, we can generate a true picture of what was the present with all the pieces in play.

Please if you have any objections to the terminology, now's the time to correct them. I'm not sure relativity has terminology for these puzzle pieces.

Tomorrow I'll introduce an STD that shows how the pieces begin to diverge when relative velocity comes into play. Things will get very complicated after that.
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Re: S.R. Defining the present

Postby ralfcis on May 16th, 2017, 11:47 am 

Double post
Last edited by ralfcis on May 16th, 2017, 11:50 am, edited 2 times in total.
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Re: S.R. Defining the present

Postby ralfcis on May 16th, 2017, 11:49 am 

Just no time to keep this thread going but I am doing the math in the background and it's open to so much interpretation that I'm worried this thread will degenerate into philosophy and then get shut down.

So here's what I'm understanding of the present so far (and will present the math at the end). It looks like the present is an individual bubble surrounding each of us. The farther away from your bubble, the more past of everything else you see. (The stars you see now are how they looked way in the past.) Even if everything and everyone around you is in the same frame, you are not all seeing the same present even though you're all sharing the same present. So if a bunch of bubbles are all moving at zero relative velocity strung out all over space, they don't coalesce, they remain separate but strung together by a calculated common present.

Is reality what you share (calculated) or what you see (subject to the speed of light delay)? If the sun disappeared, our shared present is that we don't know the sun is gone but for 8 min our present reality is that the sun is still there. This theme of apparent present and calculated present permeates relativity but which of these is actually defined as reality?

There are more facets to this question. If the present is a small bubble and length contraction is only in the direction of motion and reciprocity exists between two participants engaged in a relative velocity, then any effects we theorize about what we would see of a ship at .6c should be the same as that ship sees of us. Currently SR says we would see very localized dilation/contraction of the ship but the ship would see the same effects occurring to us on the scale of the entire universe.

But is this really true? I'll show you my math later but for now let's just put our finger to the wind. The farther anything is away from your bubble, the smaller it looks and the slower it looks. These effects are just illusory perspective but we can calculate the underlying reality.

Let's take this to the extreme and explore where the theory comes from that the CMB is an absolute frame of reference. It is both all around us and is equally distant from everything in the universe. It is as far in the past as we can see yet we can calculate a shared present with it as well (based on whether expansion of the universe has a relative velocity to it or not). It is so far away that time appears to stand still, 0 velocity relative to everything. This is apparently true but not really true. The distance from the CMB means a ship traveling .6c relative to us will not see the universe any more contracted or time dilated than we would see the same universe around the ship.

Consider the popular version of relativity that states you can't tell if the universe is rushing past you or you're rushing past the universe. That concept, as stated, requires an implied anchor point that is outside the universe. It's like the universe is a record put on a record player and the needle is fixed to the record player while the record spins underneath it. It's like the LHC is spun around stationary protons. These concepts may be valid mathematically, but they are not valid physically. You can never consider the mass of the universe spinning underneath you in the same way you can't consider hidden stagehands moving the scenery around you like we are all actually paralyzed in space. Those concepts are not physical reality, one can always trace back into the past on who experienced acceleration to get moving.

You don't need the idea that either frame can be considered stationary, all that counts is the RELATIVE motion which can be depicted any way you want in an STD. If Alice is moving, you don't ever have to consider her as the stationary frame, that is all embedded in the STD, you just need to see it.

Here is an STD at .8c of what each participant sees of the other. The view is identical, it's just the coordinate systems that make it look different. Just like Bob sees Alice in square coordinates, Alice is also seeing Bob in square coordinates but Bob looking back at himself through Alice's eyes would see the rhombic coordinates.

8crecip.jpg


The dotted lines represent the present from each perspective. When Bob is 3, he sees Alice at 1.8 her time at 2.4 ly. When Alice is 3, she sees Bob at 1.8 his time at 2.4 ly her spatial coordinate. From Bob's perspective they may age at the same rate but they do that at 2 different present times. For example, Bob is 3 at t=3 but Alice is 3 when t=5. But what if there was a perspective from which both Bob and Alice are 3 at the same time and age at the same rate. Or what if Alice and Bob had a relative velocity of .8c but had no reciprocal time dilation between them and aged at the same rate at the same present time from both their perspectives. The STD's depicting these will be developed in the next post.

Hint: a reference frame doesn't need to be stationary nor does it need to be tied to one of the participants.

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