Quick question about SR

[blike]

For awhile I've felt I understood the basic principles of special relativity, but now that someone is prodding me with all sorts of hypotheticals I find that I really don't understand it all that well.

 

Does special relativity imply that there are multiple "present realities" in the universe? In other words, can two people in two different inertial frames ever agree on what the exact present is? Is there a freeze-frame snapshot of the universe on which all observers would agree?

 

Also, why do physicists use the term "time frame"? It seems deceptive, because although two observers may be in a different "time frame" they can still interact with one another. This implies that they are both experiencing a common present reality, correct?

 

However, it seems to me at some point the present experiences of two people in two different inertial frames cannot match up entirely, or they'd experience time in the exact same way.

[eon_rider]

Does special relativity imply that there are multiple "present realities" in the universe? In other words, can two people in two different inertial frames ever agree on what the exact present is?

 

Not an expert however, I'm starting to think you can't mix talk of multiple

"present realities" and SR or GR without argument and confusion.

 

If one just takes S/GR for what it is, and does not try to talk about multiple realities then things seem to go smoothly.

 

If you are asking are there multiple present realities in a philosophical context then the debate can go full steam ahead.

 

But that may be another section of the site.

 

I keep making this mistake myself. (Mixing the two)

 

So I'm trying to know S/GR a little better, and certain areas of philosophy a little better so that I can separate the two, and not confuse apples with oranges. If it is apples and oranges? LOL

 

I hope that helps and I bet a better informed scientist, or philosopher will chime in.

 

Personally I think the question is fantastic and I get prodded about it tooo!

 

But mathematicians and scientist are going to say. Wrong section of the forum. (that's what they tell me at least...LOL....and that's OK...totaly understandable. S/GR is suppossed to be physics and only physics.)

 

But S/GR is very profound. I don't think that point is argueable.

 

best

 

Eon.

 

PS. I'm still learning.

[MetaFrizzics]

The 'multiple realities' idea is an interpretation of Quantum Mechanics by Everett: his 'many worlds' interpretation. It is totally foreign to SRT.

 

The only multiple thing in Minkowski space is the 'movable' plane of simultaneity, which cuts a different slice in spacetime for each observer with a different velocity and location.

[swansont]

Does special relativity imply that there are multiple "present realities" in the universe? In other words' date=' can two people in two different inertial frames ever agree on what the exact present is? Is there a freeze-frame snapshot of the universe on which all observers would agree?

[/quote']

 

 

No. Two events (A,B) that are spatially separated may appear to be simultaneous in one frame, while A precedes B in some frames and B precedes A in others (depending on whether the events are or could be causally related, i.e. inside or outside of the light cone)

[J.C.MacSwell]

For awhile I've felt I understood the basic principles of special relativity' date=' but now that someone is prodding me with all sorts of hypotheticals I find that I really don't understand it all that well.

 

Does special relativity imply that there are multiple "present realities" in the universe? [b']In other words, can two people in two different inertial frames ever agree on what the exact present is? [/b] Is there a freeze-frame snapshot of the universe on which all observers would agree?

 

Also, why do physicists use the term "time frame"? It seems deceptive, because although two observers may be in a different "time frame" they can still interact with one another. This implies that they are both experiencing a common present reality, correct?

 

However, it seems to me at some point the present experiences of two people in two different inertial frames cannot match up entirely, or they'd experience time in the exact same way.

 

Two people not at rest wrt each other can agree on certain points (areas) of simultaineity but not everywhere in their inertial frames.

[wormholeman]

Seems to me like you guys are talking about dimensions.

I dont know If spatial relativity implys that there are multiple realitys.

But this can go in a pretty fancy direction: http://www.krioma.net/articles/Bridge%20Theory/Einstein%20Rosen%20Bridge.htm This link talks abit about parallel universes

if you read on.

[blike]

No. Two events (A,B) that are spatially separated may appear to be simultaneous in one frame, while A precedes B in some frames and B precedes A in others (depending on whether the events are or could be causally related, i.e. inside or outside of the light cone)

Thanks, that was the answer I was looking for. Does this imply that the events are truely separate for one observer and simultaneous for another? Or is it just tricks of light? Because what we perceive as our present experience is really determined by how fast light reaches us. So perhaps the lightbulbs are truely simultaneous, but because of the constancy of the speed of light, it only appears that they light up at different times?

 

For instance, imagine I am viewing two lightbulbs in a mirror. One mirror is directly reflecting a light bulb. The other mirror beams the image to the moon onto another mirror, which then reflects it back to earth and off another mirror into my eye. They are set up so I can't visually determine which mirror is which by looking at the lightbulbs in them. The lights are both turned on simultaneously. However, in the mirror one bulb lights up faster than the other one (as the light has to travel to the moon and back). However, the true reality is that they are simultaneous. Is relativity just playing tricks with light similiar to the setup I have descibed?

 

And finally, if there were a way for me to relay information to another observer instantaneously, could I tell someone the future?

[eon_rider]

For instance, imagine I am viewing two lightbulbs in a mirror. One mirror is directly reflecting a light bulb. The other mirror beams the image to the moon onto another mirror, which then reflects it back to earth and off another mirror into my eye. They are set up so I can't visually determine which mirror is which by looking at the lightbulbs in them. The lights are both turned on simultaneously. However, in the mirror one bulb lights up faster than the other one (as the light has to travel to the moon and back). However, the true reality is that they are simultaneous. Is relativity just playing tricks with light similiar to the setup I have descibed?

 

So, it seems, you are asking about your experience of the light bulb being turned on, at different times, compared the the act of the light bulb being switched on at the same time, as experienced, by someone else...(the experimenter perhaps.)

 

My answer is sure your personal experience can be subjective!

And also have it's own physical POV.

A different point of view from the experience of the experimenter.

 

Does that mean multiple realities?

I'm not sure. It's sematics.

Sounds to me more like multiple experiences.

 

Who would argue that different people in different locations and circumstances

all have individual (different) experiences?

 

I'm not sure if that's the same as multiple realities. I don't think so.

 

S/GR can't answer this question.

 

But to me, this is not multiple realities, but multiple experiences or points of view depending on where you are located, or other factors.

Few would dispute multiple points of view.

 

In the brain many things are not happening in the order one thinks they are.

The brain does alot of gymnastics with data. See reith lectures 2003 or study neuroscience. (that may be beside the point)

 

Do you feel like you are travelling thousands of miles per hour around the sun while spinning?! No.

 

It's happening.

But you don't notice it.

 

You're not being fooled.

It's just your point of view (experience) does not need to question

"Am I really standing still, or am I moving at the speed of earth, while spinning, through space?"

 

Your personal experience will be connected to where you are now.

What you are doing now. (and in most cases, your experience is informed by who you are also)

 

In another example the person on the other side of the earth will say you are very far away from them, but you'll say they are very far away from you.

Is this multiple realities, or just multiple POV's with regards to one's location?

(as soon as you decide who is object A and who is object B and pick your reference frame for measuring, then the issue is resolved.) I think.

 

That’s not multiple realities, rather multiple experiences. (or simply multiple locations on earth existing simultaneously)

 

Just my 2 cents. I hope i didn't confuse anyone too much. LOL.

 

It's all fine.

 

best,

 

Eon.

 

 

 

PS. I'm not sure, but could a good mathematician or expert in SR be able to mathematically show that?

 

You and the scientist, even if standing back to back, are actually in two different inertial reference frames?

 

That's my question?

 

The maths of it is well beyond me.

But again, this may not be a question for SR or GR to answer.

Rather another line of empirical inquiry

[swansont]

Thanks' date=' that was the answer I was looking for. Does this imply that the events are truely separate for one observer and simultaneous for another? Or is it just tricks of light? Because what we perceive as our present experience is really determined by how fast light reaches us. So perhaps the lightbulbs are truely simultaneous, but because of the constancy of the speed of light, it only appears that they light up at different times?

 

For instance, imagine I am viewing two lightbulbs in a mirror. One mirror is directly reflecting a light bulb. The other mirror beams the image to the moon onto another mirror, which then reflects it back to earth and off another mirror into my eye. They are set up so I can't visually determine which mirror is which by looking at the lightbulbs in them. The lights are both turned on simultaneously. However, in the mirror one bulb lights up faster than the other one (as the light has to travel to the moon and back). However, the true reality is that they are simultaneous. Is relativity just playing tricks with light similiar to the setup I have descibed?

 

And finally, if there were a way for me to relay information to another observer [i']instantaneously[/i], could I tell someone the future?

 

Simple delay due to travel oflight can be accounted for easily - you do this to get proper synchronization of clocks. The effects of SR are due to relative motion, and since no observer can claim to be in a preferred frame, that's where the real confusion kicks in. But it's not just a "trick of the light," because nobody can point to a single frame of reference and say that it is the reality, and everything else should be referenced to that.

 

If yould convey information instantly, you could tell someone what was going to happen before they could observe it happening. e.g. You flip a light switch and turn on a light, and convey to a person one light-minute away what you did. Then they know that in one minute the light will turn on.

[eon_rider]

Swansont wrote: Simple delay due to travel oflight can be accounted for easily - you do this to get proper synchronization of clocks. The effects of SR are due to relative motion, and since no observer can claim to be in a preferred frame, that's where the real confusion kicks in. But it's not just a "trick of the light," because nobody can point to a single frame of reference and say that it is the reality, and everything else should be referenced to that.

 

If yould convey information instantly, you could tell someone what was going to happen before they could observe it happening. e.g. You flip a light switch and turn on a light, and convey to a person one light-minute away what you did. Then they know that in one minute the light will turn on.

 

This is a great answer. Clear as day.

So I guess the question can be answered using SR.

cool.

[J.C.MacSwell]

If yould convey information instantly' date=' you could tell someone what was going to happen before they could observe it happening. e.g. You flip a light switch and turn on a light, and convey to a person one light-minute away what you did. Then they know that in one minute the light will turn on.[/quote']

 

If that person then relays the information to someone in their neighbouhood driving at high speed toward you, then the driver instantly (his instantly/simultaneity) relays the information back to you... you will receive the information before you sent it!

If you then change your mind and don't send a signal then we are all in trouble!

 

Edit:the driver could (assuming instant messaging is possible) have relayed the message to someone in your neighbourhood that agreed on the instantly/simutaneity (another driver speeding in the same direction at rest wrt him) who then could relay it to you conventionally (light speed radio from just outside your house) and you get the same result...a signal back in time, in this case via a network of signals none of which went back in time from any sender or receivers POV for any signal they took part in.

 

Hope that makes sense!

[swansont]

If that person then relays the information to someone in their neighbouhood driving at high speed toward you' date=' then the driver instantly (his instantly/simultaneity) relays the information back to you... you will receive the information before you sent it!

If you then change your mind and don't send a signal then we are all in trouble!

[/quote']

 

I don't think so. Information that is hypothetically sent instantaneously does not go back in time, it just doesn't go forward.

 

Of course, the pitfall here is that once you've decided to violate one physical law in a gedanken experiment, you have to decide how to apply all the rest. You no longer have a self-consistent framework, so many different results are possible, depending on your interpretation of things.

[eon_rider]

It seems one should continually stay close to a well tested self-consistent framework like SR or GR in order to stay out of theoritical trouble where strange, impossible, or unhelpful results occur on the white board.

 

So, I guess, one has to venture towards new ideas within physics very carefully and slowly if at all, after really understanding the foundations of S/GR or any area of physics.

[J.C.MacSwell]

I don't think so. Information that is hypothetically sent instantaneously does not go back in time' date=' it just doesn't go forward.

 

Of course, the pitfall here is that once you've decided to violate one physical law in a gedanken experiment, you have to decide how to apply all the rest. You no longer have a self-consistent framework, so many different results are possible, depending on your interpretation of things.[/quote']

 

An instantaneous message in one inertial frame, while neither forward or backward in time in that frame, corresponds mathematically to a back in time message in others, depending on the relative velocities of the frames and the direction of the message. Correct?

[swansont]

An instantaneous message in one inertial frame, while neither forward or backward in time in that frame, corresponds mathematically to a back in time message in others, depending on the relative velocities of the frames and the direction of the message. Correct?

 

Yes, but that's not what was described. If you draw a spacetime diagram (t vs x), the signal has zero slope, not a negative slope. A sends B a message instantly. B sees that message as "from the future" and any response he sends will be seen by A as "from the future" but not, AFAIK, seen before A sent his original message. You can't bootstrap this back in time in A's frame, unless there's some other assumption that I'm missing.

[J.C.MacSwell]

Yes, but that's not what was described. If you draw a spacetime diagram (t vs x), the signal has zero slope, not a negative slope. A sends B a message instantly. B sees that message as "from the future" and any response he sends will be seen by A as "from the future" but not, AFAIK, seen before A sent his original message. You can't bootstrap this back in time in A's frame, unless there's some other assumption that I'm missing.

 

My assumptions were that A and B were at rest in one inertial frame one light minute apart.

 

If I was B I would see I would see (calculate) the message as from the present without lag then see the light flash one minute later.

 

If I then signal my "driver" (let's call him c) conventionally by radio outside my house who is driving a significant portion of lightspeed (say 86%) toward A.

 

If c then signals driver "D" unconventionally/instantaneously (read not accepted physics but same as the A to B signal) driver D being at rest wrt C.

 

If D, having received the signal happens to be just outside the house of A and signals him conventionally (conventionally saves them from arguing about instantaneity even over the short distance) while travelling past (again 86% Light speed )

 

A would receive the last signal almost 30 seconds before sending the first, assuming I haven't made any mistakes and my assumptions are correct (of course they aren't because instantaneous messaging and SR are not compatible)

 

While A and B would agree their signal had "zero slope", and C and D would agree their signal had "zero slope", each pair would see the other pair's signal as having negative slope.

[eon_rider]

OH...thanks guys!

 

It was all clear as day until you had to gedanken

a brand new senario...LOL.

 

I'm just going to stick to Blike's original gendunkin's

as I understand swansont's explanation of those.

 

No worries,

 

Eon.

[swansont]

My assumptions were that A and B were at rest in one inertial frame one light minute apart.

 

If I was B I would see I would see (calculate) the message as from the present without lag then see the light flash one minute later.

 

If I then signal my "driver" (let's call him c) conventionally by radio outside my house who is driving a significant portion of lightspeed (say 86%) toward A.

 

If c then signals driver "D" unconventionally/instantaneously (read not accepted physics but same as the A to B signal) driver D being at rest wrt C.

 

If D' date=' having received the signal happens to be just outside the house of A and signals him conventionally (conventionally saves them from arguing about instantaneity even over the short distance) while travelling past (again 86% Light speed )

 

A would receive the last signal almost 30 seconds before sending the first, assuming I haven't made any mistakes and my assumptions are correct (of course they aren't because instantaneous messaging and SR are not compatible)

 

While A and B would agree their signal had "zero slope", and C and D would agree their signal had "zero slope", each pair would see the other pair's signal as having negative slope.[/quote']

 

 

OK, I had "one inertial frame" stuck in my head, which was the example I had given. You are correct - causality indeed gets violated when you have pairs of observers in two different frames, as the return signal precedes the original one.

 

Here are some Minkowski diagrams that describe both scenarios

[J.C.MacSwell]

OK' date=' I had "one inertial frame" stuck in my head, which was the example I had given. You are correct - causality indeed gets violated when you have pairs of observers in two different frames, as the return signal precedes the original one.

 

Here are some Minkowski diagrams that describe both scenarios

 

Thanks, great link. The "fun" thing about it is that even without FTL messaging it puts serious strain on any common sense definition of what "now" means any distance from the point you are at.