Simultaneity and t=0 - SRT

[Fredrik]

"If we have two or more observers [ RF's ] at relative v is t=0 for light events simultaneous for both or all of them?"

You're not really making sense ("at relative v"? "light events"?), but it's clear that you're asking something about "t=0" in several different inertial frames. Imagine a spacetime diagram where we're only drawing one spatial dimension (plus one time dimension of course). The diagram represents the coordinates of one inertial observer. t=0 is a straight line in the diagram. Now suppose that there's another inertial observer, whose motion is represented by the line x=vt in your spacetime diagram.

This second observer will not agree with you about which events have t'=0, unless v=0. (I'm putting a prime on all of his coordinates to distinguish them from yours). The line that is t'=0 in his coordinates is t=vx in your coordinates, assuming that you're both using the same event as the origin.

What this means is that the two of you won't agree about which "slices" of spacetime you should think of as space. The angle between his slices and yours is arctan v.

 

[Tubbythin]

I am not disagreeing with your assessment when I say this, but I disagree that the t=0 is unimportant.

Possibly it is unimportant to SRT but that is just SRT.

Not at all. There is no Universal co-ordinate system, we do not walk past Universal co-ordinate gridlines on our way to work in the morning. Problems can be set-up with whatever co-ordinate system we find the easiest to do calculations and transformations in. t=0 is merely the location of one of the axes of this imaginary 4-D co-ordinate system and has no physical reality or significance.

It is something that has bugged me for ages and how confusing this issue is when dealing with non-simultaneity or relative momenets of recording events for relative v observers...
Now that you all have explained the SRT position which I find rather intriguing It starts to make sense why I have had so much difficulty in the past.

This is precisely why it pays to understand the area of physics you want to dispute before trying to dispute it.

 

[Cuddles]

Actually don't bother with it... the thead has been answered. It has been stated that according to SRT 't' can be anything you want it to be and that it is arbitary.

thats all I need to know...

That may be all you need to know, but it's wrong and is not what anyone else has told you. What is arbitrary is one value of t any one particular point. Every other value of t is measured relative to that, and is not arbitrary in the slightest.

Also, as has already been pointed out to you but bears repeating, this has nothing to do with relativity. Anything that involves a coordinate system, whether it's physics, maths or something else entirely, works in exactly the same way. The way the coordinates behave and interact may vary, but having to define arbitrary points and measuring things in relation to them is, well, pretty much the definition of a coordinate system.

 

[69dodge]

try this contra:

If 't' can equal say 10 minutes from now when we get to 't' isn't it t=0?

if 't' equals 10 minutes form now then that event is in the future and is yet to occur.
if 't' equals -10 minutes from now then that event is in the past and is no longer observable except as a historical record.

but even so t= -10 must have occurrered at t=0


does that make sense?
and then if you can understand it, is it a correct understanding?

You are making things too complicated, I think.

When someone asks you for the time, do you look at your watch and say, e.g., "It's a quarter after five"? Or do you say, "What a silly question! Obviously, the time right now is now, just as it always is"?

 

[ozziemate]

Ah, but it's much easier to do the math in your head when one of the two numbers is 0

now that's the truth ....ha

 

[ozziemate]

You are making things too complicated, I think.

When someone asks you for the time, do you look at your watch and say, e.g., "It's a quarter after five"? Or do you say, "What a silly question! Obviously, the time right now is now, just as it always is"?

I have found that it pays to be a bit more precise when discussing SRT.

In a way I guess I am only exploring that which is so obvious no one ever bothers with it.
that all events for an observer regardless of his relative v always occur at the moment he can perceive them which is t = hsp [ between past and future ]

It may seem unimportant but when discussing relative t=hsp it is very important I feel to be very clear on what you are talking about. [ even if wrong]

"if you don't know how wrong you are then you will never learn"

The way I see SRT regarding time is this:

"every observer regardless of relative velocity has a unique world time line and when the relative v=0 the two frames share that same time line. When the relative velocity >0 then the observers in question do not share the same world time line. Meaning essentially that relative velocity creates an entire universe that is unique to that observer in question.
As his t=hsp is now no longer the same or equal to as the other observer.

The greater the difference in velocity the more different the universes.

SRT creates a multi time [hsp] universe as per relative time. But what this actually means is a multi verse or multiple universes unique to each observer is the norm. [ when at rel. v ] Due to the fact that according to SRT the observers no longer share the same t-hsp."

do you agree...?

* hsp = hyper surface of the present.

 

[not daSkeptic]

YWhen someone asks you for the time, do you look at your watch and say, e.g., "It's a quarter after five"? Or do you say, "What a silly question! Obviously, the time right now is now, just as it always is"?

To extend this analogy, I could say any of the following and be correct:

• The time is currently 14:25, as measured from 00:00 (midnight in my local time zone).
• The time is currently 02:25 as measured from 00:00 (noon in my local time zone).
• The time is currently 00:00 as measured from right now.
• The time is currently 1223501195 as measured from 0 (midnight, GMT, January 1, 1970).
• The time is currently -34500 as measured from 0 (midnight in my local time zone, tomorrow).

Each of the above represents the exact same point in time. I just used a different reference point for each. As Cuddles stated, the choice of a reference point is entirely arbitrary, but all of the other values fall relative to that.

I could keep going and demonstrate how the reference point does not have to be zero:

• The time is currently 02:25, as measured from 12:00 (in my local time zone).
• The time is currently 03:50 as measured from 10:35 (in my local time zone).
• The time is currently 14:25 as measured from right now.
• The time is currently 300 as measured from 1223500895 (five minutes ago).
• The time is currently -642 as measured from 1223501837 (10 minutes, 42 seconds from now).

These are all the same time as before. The only difference is the chosen reference points are non-zero.

 

[Reality Check]

I have found that it pays to be a bit more precise when discussing SRT.

In a way I guess I am only exploring that which is so obvious no one ever bothers with it.
that all events for an observer regardless of his relative v always occur at the moment he can perceive them which is t = hsp [ between past and future ]

It may seem unimportant but when discussing relative t=hsp it is very important I feel to be very clear on what you are talking about. [ even if wrong]

"if you don't know how wrong you are then you will never learn"

The way I see SRT regarding time is this:

"every observer regardless of relative velocity has a unique world time line and when the relative v=0 the two frames share that same time line. When the relative velocity >0 then the observers in question do not share the same world time line. Meaning essentially that relative velocity creates an entire universe that is unique to that observer in question.
As his t=hsp is now no longer the same or equal to as the other observer.

The greater the difference in velocity the more different the universes.

SRT creates a multi time [hsp] universe as per relative time. But what this actually means is a multi verse or multiple universes unique to each observer is the norm. [ when at rel. v ] Due to the fact that according to SRT the observers no longer share the same t-hsp."

do you agree...?

* hsp = hyper surface of the present.

You are getting your notation incorrect. HSP is a 4-vector, i.e. (x,y,z,t). t is a 1-vector. You cannot put a 1-vector equal to a 4-vector. What you really meant was: t = t_HSP. And the longer English way to state this is: t = the observer's present time.

The bit in quote is essentially correct but...
Each observer in a reference frame does not get their own universe. They get their own set of coordinates in that reference frame within the same universe (no "multi time [hsp] universe").
The definition of a reference frame

A reference frame is an observational perspective in space at rest, or in uniform motion, from which a position can be measured along 3 spatial axes. In addition, a reference frame has the ability to determine measurements of the time of events using a 'clock' (any reference device with uniform periodicity).^WP

 

[Reality Check]

And you are right: It is obvious that all observers experience their present events at their present time. It is a bit hard for them to experience past or future events at their current time.

 

[ozziemate]

And you are right: It is obvious that all observers experience their present events at their present time. It is a bit hard for them to experience past or future events at their current time.

Finaly we have an agreement about something....ha...thanks
"The obvious is sometimes the hardest to explain." The self evident, the things we take for granted as being solved etc etc, are sometimes virtually intractible in changing.

any ways thanks again

 

[Reality Check]

Finaly we have an agreement about something....ha...thanks
"The obvious is sometimes the hardest to explain." The self evident, the things we take for granted as being solved etc etc, are sometimes virtually intractible in changing.

any ways thanks again

Actually it is easy to explain: The definition of present time is that it is the time at which observers see events that happen at their present time. Thus by definition observers see present events at their present time.

 

[69dodge]

You don't see events as soon as they happen, unless they happen right in front of you. If they happen far away, you see them some time after they happen, because the light by which you see them takes some time to get to you from them.

Even after correcting for the light's travel time, thereby calculating the events' earlier "real" times of occurence, observers in relative motion still generally disagree about the amount of time between events (and also about the distance between events.) But they agree about the spacetime interval between events, so it's not quite right to think of different observers as inhabiting completely separate universes. Their universes are different in some ways, but the same in other, more important, ways.

 

[Dancing David]

I have found that it pays to be a bit more precise when discussing SRT.

In a way I guess I am only exploring that which is so obvious no one ever bothers with it.
that all events for an observer regardless of his relative v always occur at the moment he can perceive them which is t = hsp [ between past and future ]

It may seem unimportant but when discussing relative t=hsp it is very important I feel to be very clear on what you are talking about. [ even if wrong]

"if you don't know how wrong you are then you will never learn"

And if you ignore the evidence you will always be a fool.

The way I see SRT regarding time is this:

"every observer regardless of relative velocity has a unique world time line and when the relative v=0 the two frames share that same time line. When the relative velocity >0 then the observers in question do not share the same world time line. Meaning essentially that relative velocity creates an entire universe that is unique to that observer in question.
As his t=hsp is now no longer the same or equal to as the other observer.

more sillyness, by you defintion then there is no universe. The nature of time as a relative reference is what it is, you can't just close your eyes and make it go away.

this is an area where you might have to check your ego and intuition.

It is intuitive to think of time as a universal and that simultaniety exists. the evidence says not. You also can not say that every moving object is in a different universe, you can but it makes no sense. In the 4d sense, time is another coordinate, you are saying that for every moment of relative displacement to a coordinate network and new universe is created.

Why, because the 'origin' is always zero, so for every point the coordinates are zero.

Same same, you aren't saying it about any other dimension.

The greater the difference in velocity the more different the universes.

the farther across the room the more different the universe.

SRT creates a multi time [hsp] universe as per relative time.

Nope.

you just don't like the resolution.

But what this actually means is a multi verse or multiple universes unique to each observer is the norm. [ when at rel. v ] Due to the fact that according to SRT the observers no longer share the same t-hsp."

do you agree...?

* hsp = hyper surface of the present.

Nope.

 

[Dancing David]

Here is the deal Ozzie, if we have a three d cube, and many points in it, you are saying that "If I call all points the origin, then there are no coordinates, because from the POV of each point it is the origin. And the origin is (0,0,0) therefore there is no distance. All points are the same."

t=0

is an abstraction, it does not exist, any more than the photons.

 

[plumjam]

In relation to experiencing the present, all this stuff about light etc.. is just misleading. Anything you experience via the senses is inevitably going backwards in time.. even if you're being held down and having a torch shone directly in your eye.
If your mission is really to get as close to present experience/reality as possible your first step will be to shut off the senses. When you do that you have thoughts, which are still not entirely immediate. After that is consciousness itself, which is the most immediate (obviously).
This is what meditators have been doing for millenia.
Go down that path. Forget about light and all that.

 

[Dancing David]

Wow, PJ I sure am glad you didn't teach me meditation.

 

[ozziemate]

In relation to experiencing the present, all this stuff about light etc.. is just misleading. Anything you experience via the senses is inevitably going backwards in time.. even if you're being held down and having a torch shone directly in your eye.
If your mission is really to get as close to present experience/reality as possible your first step will be to shut off the senses. When you do that you have thoughts, which are still not entirely immediate. After that is consciousness itself, which is the most immediate (obviously).
This is what meditators have been doing for millenia.
Go down that path. Forget about light and all that.

I agree almost entirely..
and I thank you for your advice.
I have often wondered why I entertain myself with posting to this forum when a sunrise sitting in the dunes over looking the roling surf would far more nurturing.
It is easy to leave reality behind and enter the realm of the mind and it's constant desire to use abstraction. A labyrinth and a devils playground of "if this and if that and why not do this and why not do that" and this I guess is in part of my purpose with this playing around with scientifc abstraction, to learn to cope with the desire to escape from reality in to someone else ideas and conceptualisations thus leaving your own behind somewhere lost in ego centric pressure applied by some people who's only intersts and intent is to maintain power over others.

Drawing pretty pictures in our minds of what reality is at a level that is beyond direct observation with those senses.

True, using the sense immediately implies
living in the past in a sense, but what would be more true is that the time it takes for informaion to make sense throws a person into a delayed life experience, thus being able to clear you mind of uneccessary baggage and beliefs that are mere obstacles to growth and get down to the nitty gritty of what actually is, can be very rewarding.

To get to the immediate moment is only even possible if mental constructs that inhibit the experience are minimised or removed.
Unfortunately personal experience is impacted on the baggage carried by others hence this and other threads in learing how to deal with the amount of material people cling to to afford them their comfort zones certainty.

PlumbJam, I can see from your rare and occasional posts to teh war zone that you know what I am talking about and I ask if you have any other published material you would care to share...if so can you send me a pm.

 

[Dancing David]

Bad sign my friend, the four cornered room of your mind is not a good place to live, there are doors to the outside.

Unless you have already kissed the peach Blossom Demon, for then it is hard to turn aside. Just like riding in the Magic Sky Pixie Chariot of Wonder, reality is sort of dull, but much more worth it than the Woolfest of Muddled Thinking and loose association.

Plum Jam is not to be trusted, he is a minion of the MSP.

There is no such thing as consciousness, there is only a body, if you don't take care of it, that is a shame.

You know that this debate and those thoughts are unhealthy, go to the beach,

"Take the dreams that should have died
The ones that kept you lying awake
When you shouldve been all right
And throw em all away

With the time I waste on the life I never had
I couldve turned myself into a better man"

Throw it All Away, Toad the Wet Sprocket

 

[NobbyNobbs]

try this contra:

If 't' can equal say 10 minutes from now when we get to 't' isn't it t=0?

if 't' equals 10 minutes form now then that event is in the future and is yet to occur.
if 't' equals -10 minutes from now then that event is in the past and is no longer observable except as a historical record.

but even so t= -10 must have occurrered at t=0


does that make sense?
and then if you can understand it, is it a correct understanding?

*

What you are doing is redefining your coordinate system as you go. To use the analogy provided by others, it's like traveling down the highway and the truck carrying the mile marker signs is traveling alongside you with mile marker 0 in the back. Just because you are always at mile marker zero does not mean you are zero miles from Boston.

It is interesting that intuitively in the hypothetical year London was declared open it must have occurred for the observers of that event in their moment [ their NOW or t=0 ]


after all what is t=-1687 any way. The value -1687 is related to zero yes...

so even if you can give t any value you choose it will still relate back to zero....hmmmmm interesting...

Actually don't bother with it... the thead has been answered. It has been stated that according to SRT 't' can be anything you want it to be and that it is arbitary.

thats all I need to know...

Folks, the above quotes are helping to verify what I fear: that Ozzie will take from this discussion only those snippets that help prove his earth-shattering theory, and ignore the rest. See his other threads if you doubt this.

Ozzie, zero has no special meaning. The only reason we tend to start our coordinate systems off with it is because of the way our mathematics is set up; adding and subtracting zero is easy. That's the only reason. You don't have to believe this, but if you don't you'll end up wasting a whole lot of your time.

"if you don't know how wrong you are then you will never learn"

You have no idea how wrong you are. Or how ironic this statement is.