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Author Topic:   Is Faster Than Light travel the wrong question?
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 10 of 81 (533367)
10-30-2009 12:12 PM
Reply to: Message 1 by Michamus
10-29-2009 10:43 AM


So my question is this, is FTL or LS travel really what we are after?
Faster than light speed, as I understand it, is a nonsensical question.
As I understand it, or as Cavediver explained it and i think I undestood it, lol:
Everything (with mass) travels at the speed of light (300,000 m/s) we just do so in the temporal direction, which is to say, we experience time at 300,000 m/s.
When you speed up, you are doing so in the spacial direction.
By doing so, you are taking that speed of light (experienced time) from the temporal direction and rotating it to the spacial direction, so "speed" thru space is basically "time experienced". So when you speed up you are basically just shortening experienced time.
Light doesn't experience time (0 rest mass), and it travels at a *speed* of 300,000 m/s; so as you start to speed up spacially, and equally start to experience time slower, the closer you get to not experiencing time at all, the closer you get to 300,000 m/s.
So, if I understood cavediver correctly, you can't experience time any less than not experiencing time at all (as with light) so you can't exceed 300,000 m/s - IOW, you can't experience time any *slower* than 300,000 m/s.
I hope this made sense. lol
- Oni
Edited by onifre, : No reason given.
Edited by onifre, : No reason given.

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onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 17 of 81 (533454)
10-31-2009 2:20 AM
Reply to: Message 15 by Perdition
10-30-2009 2:09 PM


Re: fantasy
The science at one time said breaking the sound barrier was impossible, so it's also possible (though I would admit unlikely) that the light speed limit is not quite as absolute as we think it is.
Agreeing as we always do (on most things) it pains me to have to interject - lol. Actually, the speed of light as a constant is a fact of nature; in fact, one could say a law of physics.
I like how a lot of arguments come back to the same line of reasoning; what objective evidence are you using to state that it might not be "absolute," or a constant, as I called it?
- Oni

This message is a reply to:
 Message 15 by Perdition, posted 10-30-2009 2:09 PM Perdition has replied

Replies to this message:
 Message 35 by Perdition, posted 11-02-2009 1:32 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 37 of 81 (533735)
11-02-2009 3:41 PM
Reply to: Message 35 by Perdition
11-02-2009 1:32 PM


Re: fantasy
I agree, it probably is a constant and an absolute barrier on speed in "future direction" though it may hint at being able to travel in the "past direction", i.e. time travel.
Err, if I'm understanding relativity correctly, there is no "absolute" time (universal time) from which to travel back or forward in time from.
But I'm always loathe to say we understand it completely and can say with 100% certainty that there is absolutely no way at all possible to over come this.
I think what Einstein's theory does, is do away with absolute time and space - which does away with the human notion of forward and backwrads in "time".
I may be wrong in my understanding though.
- Oni

This message is a reply to:
 Message 35 by Perdition, posted 11-02-2009 1:32 PM Perdition has replied

Replies to this message:
 Message 39 by Perdition, posted 11-02-2009 4:15 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 40 of 81 (533750)
11-02-2009 4:41 PM
Reply to: Message 39 by Perdition
11-02-2009 4:15 PM


Re: fantasy
As I understand it, there's no absolute speed at which time passes, however, there is an absolute direction.
Not at (c) - which is to say, not for anything with 0 rest mass.
And based on the ruler explanation that cavediver has given, and you've also repeated, it would appear that if the ruler kept rotating so that it pointed diagonally downward, you would be moving in space -->and --> in time, however, you would be moving backwards in time.
Yes, but that's just an analogy. What must be remembered in that analogy is that the speed of light is the constant (or limit) that prevents the ruler from pointing downward.
Once you reach the limit, you are not experiencing time (think of a photon). To a photon emittied from the Big Bang, time has not passed at all. So it makes no sense to think that something at (c) can go backward in time when something at (c) isn't really going forward in time. Time is an irrelevant factor.
Positrons and anti-protons behave the same way as electrons and protons that are travelling backwards in time.
But how could that be if they don't experience time past at all?
- Oni

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 Message 39 by Perdition, posted 11-02-2009 4:15 PM Perdition has replied

Replies to this message:
 Message 41 by Perdition, posted 11-02-2009 4:55 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 42 of 81 (533759)
11-02-2009 5:20 PM
Reply to: Message 41 by Perdition
11-02-2009 4:55 PM


Re: fantasy
I thought the speed of light was the length of the ruler, and it's angle indicated it's "time movement" and it's "space movement" showing that as you increase one, you decrease the other.
Hmm, I don't know how you're conceptualizing it.
When the ruler is straight up, which means you are not moving in space, you are still at the speed of light (temporally) - which means that you are experiencing time at 300,000 m/s.
When you speed up spacially, the fastest you can go (imagining that you had no mass) is 300,000 m/s.
So the ruler pointing straight up is at the speed of light (temporally), and as the ruler goes down (speeding up spacially) in our analogy you are increasing your spacial speed to the limit of 300,000 m/s.
So the speed of light limit is both temporal and spacial.
Oni writes:
But how could that be if they don't experience time past at all?
Perdition writes:
I don't know
Well, if I could attempt to explain - my point was that backward and forward in time are only relevant concepts to things that have mass, and its only an intuative concept to us at that.
What relativity explains is that that intuative notion is done away with because there is no absolute space, speed, direction, size or time.
It's only relative to the observer.
If you can picture the future as a road (think a long never ending road that has everything a normal road has - houses on the sides, street lights, people, etc.) - What you consider the future is all of the houses and street lights and people who are already ahead on that road, you are travelling towards them. IOW, there is no universal future, only a future relative to where you are standing and about to begin your journey from.
I'd like cavediver to chime in, but I think I'm correct for the most part as far as I understand it.
If not, I'm sure I'll get the *bullocks* stamp, LOL.
- Oni

This message is a reply to:
 Message 41 by Perdition, posted 11-02-2009 4:55 PM Perdition has replied

Replies to this message:
 Message 43 by Perdition, posted 11-02-2009 5:27 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 45 of 81 (533765)
11-02-2009 5:47 PM
Reply to: Message 43 by Perdition
11-02-2009 5:27 PM


Re: fantasy
If you keep rotating the ruler,
That's just the thing, you cannot. Conceptually it seems like you can, but once you reach the spacial constant of (c) you don't experience time anymore (hypothetically if you could reach "c").
Its the same as the notion of time and space at the quantum level being irrelevant.
backwards time travel.
Yes, but think about it - backwards in time relative to what?
And protons, electrons, positrons and anti-protons have mass, so they experience time.
Right, but the notion of universal time is done away with in Einsteins theory, which does away with the intuative notion of forward and backward in time.
Time is a dimension - past, present, future, has always existed.
Think about it this way, in a spacial dimension sense: If you walk toward me here in Miami, you wouldn't say that I haven't happened yet, right? I'm here and you are travelling toward me. Likewise, if you consider time a dimension, then there is no future that you're going towards, nor a past that you are moving away from.
All moments in "time" exist.
- Oni
Edited by onifre, : No reason given.

This message is a reply to:
 Message 43 by Perdition, posted 11-02-2009 5:27 PM Perdition has replied

Replies to this message:
 Message 46 by Perdition, posted 11-02-2009 5:56 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 47 of 81 (533767)
11-02-2009 6:11 PM
Reply to: Message 46 by Perdition
11-02-2009 5:56 PM


Re: fantasy
So, you're saying that once you reach the point of no time, there is no time in which to keep rotating the ruler?
If I am not misunderstanding it myself, once you reach the point of not experiencing time, then yes.
Think about it like this, we experience time at 300,000 m/s, however, if you were at that speed, then what would you be experiencing?
To what we currently experience. Our past becomes the future.
But what we currently experience is not a universal now from which we can travel back in time from.
True, but in all other dimensions, you can reverse course.
Ah, it would seem so, but again, relativity says no.
You have a place from which you started from - a "right here" that you started your journey from. But let me ask you, relative to the Sun, if you walk to Miami, are you going North or South? And if you turn around would you be headed in the other direction.
Likewise, if you head to Miami, relative to the Sun, are you going up or down, left or right?
So can you really reverse course, or does it just feel like you can?
Remember, no universal space, time, direction, speed or size - it's all relative to the observer.
- Oni

This message is a reply to:
 Message 46 by Perdition, posted 11-02-2009 5:56 PM Perdition has replied

Replies to this message:
 Message 48 by Perdition, posted 11-02-2009 6:19 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 49 of 81 (533772)
11-02-2009 6:28 PM
Reply to: Message 48 by Perdition
11-02-2009 6:19 PM


Re: fantasy
You're not moving north or south, but you are definitely moving in a direction, and can then reverse direction, regardless of the reference frame.
Right, but you are reversing direction from your frame of reference. But with no universal place in space, you are not moving from north then going south (or left/right, up/down). You are simply moving about in the spacial dimensions.
Likewise, with time - you can reverse direction from your moment in time (hypothetically) but with no universal "time" frame, you are not going toward a future or leaving a past - its all one and the same. You are simply moving about in the time dimension.
- Oni

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Replies to this message:
 Message 56 by Son Goku, posted 11-03-2009 4:08 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 57 of 81 (533937)
11-03-2009 4:52 PM
Reply to: Message 56 by Son Goku
11-03-2009 4:08 PM


Re: Spacetime
Hi SonGoku,
Thanks for the detailed explanation.
One such example is travelling into your own past.
Let's say you want stay in the same place but travel to ten seconds ago, you obviously can't. For you the reason is because it's in the past.
For somebody moving past you at high speeds because they'll label events differently they'll see your "now" and your "ten seconds ago" as occuring at the same time, but at different points in space. For them the reason you can't move between these two events is because they occur at the same time and you don't have time to move between them.
Question: No matter what, though, causality cannot be violated, right?
These are subjective reasons, the objective reason is that the events are not connected in spacetime. Not being able to move back in time is just one subjective way of viewing the disconnectedness of two events.
If you don't mind, I'll try to explain it just to see if I understood it:
Every observer will agree on the spacetime distance, but not necessariliy on the time it took between events - but, no matter what, the events can never be reversed. This would violate causality, right?
Causality is an axiom of Minkowski spacetime, right?
Also: Have I understood it correctly, that all moments in "time" already exist, and and since there's no universal time (just as there's no universal space) there is no point in time from where one could go back from?
In other words, and bare with my layman explanations as this is just for my understanding - forward and backward in time are nonsensical terms in Einstein's model of spacetime (or Minkowski spacetime)...?
Thanks again,
- Oni

This message is a reply to:
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Replies to this message:
 Message 58 by Perdition, posted 11-03-2009 5:07 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 60 of 81 (533941)
11-03-2009 5:43 PM
Reply to: Message 58 by Perdition
11-03-2009 5:07 PM


Re: Spacetime
While we wait for Son Goku, doesn't this imply determinism or even fatalism?
Don't think of it philosophically, think of it in a dimension sense.
Lets ignore time for a second (no pun intended, lol) - I could equally say all north/south - up/down - left/right already exist.
North/south, up/down, left/right are subjective expressions of moving about in our spacial dimensions.
Likewise, forward and backward in time are only subjective expressions of our experience in the time dimension.
Intuitively we think there's a north/south up/down left/right, likewise, we intuitively think there's a forward and possible backward in time. But there isn't. Einstien's spacetime is dimensional, so there is no absolute point in space or time from where you can go north/south up/down left/right (in the spacial dimensions) -and- no forward/backwards (in the time dimension).
What time describes is the distance between events (relative to the observer this time between events changes) - In SonGoku's example, for you it was ten seconds, but say for me travelling in an airplane above you they happened at the same "time".
We both agree on the distance, we just disagree on the time it took to get there.
But, one key thing to remember is the events themselves.
Lets say the event was you walking from the front of your house(A) to the back of it(B) - (lets call it a distance of 100ft)
No matter where the observer is (you at the events, me on a plane watching the event from above, or SonGoku on Venus) while we'll disagree on the time it took to get from position (A) to position (B), none of us will see them backwards (B happening before A).
This would violate the axiom of causality that, if I'm not mistaken, cannot be violated in any geometry that describes our spacetime.
- Oni
Edited by onifre, : No reason given.

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Replies to this message:
 Message 62 by cavediver, posted 11-03-2009 6:39 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 67 of 81 (534002)
11-04-2009 9:11 AM
Reply to: Message 62 by cavediver
11-03-2009 6:39 PM


Re: Spacetime
This is essentially the heart of the "causality" you have been hooked on.
Any pair of events can be placed into one of three categories: space-like separated, time-like separated, and null separated. Time-like means that a path through space-time can be taken between the two events, such that c is never exceeded. All observers, no matter their motion, will agree on which event is in the past and which is in the future (SG made a slight slip here.) Space-like means that no sub-light path can be taken between the two events. In this case, which event occurs first is observer-dependent. There is no such thing as one event occuring later than the other.
Thanks for that detailed explanation cavediver.
A good example would be me firing a pistol on Earth at 23:00 GMT, and you firing a pistol on Mars at 23:05 GMT. We can have the most perfectly synchronised watches ever built, but in NO ABSOLUTE WAY can it be said that I fire first!! Null-separated is the in-between state where a light-ray can connect the two events.
Can you explain in a little more depth how it is that one couldn't say who fire first?
Does it have to do with not being able to exceed (c)?
Just to add some spice, not all space-times admit such a causal structure. It is possible to have non-time-orientable space-times where even time-like separated events can have their time-ordering reversed! But we're getting into messy territory here
QM...?
just to stress - if two events are space-like separated, they will appear space-like separated to ALL observers, no matter their motion. Likewise, null-separated events will always be seen as null separated.
Can you explain this in a little more depth too?
What maintains this consistency?
Thanks again,
- Oni

This message is a reply to:
 Message 62 by cavediver, posted 11-03-2009 6:39 PM cavediver has replied

Replies to this message:
 Message 68 by cavediver, posted 11-04-2009 10:54 AM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 70 of 81 (534031)
11-04-2009 1:31 PM
Reply to: Message 68 by cavediver
11-04-2009 10:54 AM


Re: Spacetime
In SR, there is no state of rest. All states of motion are equally valid. There is no preferred frame of reference. One observer may see one gun fire first and then the second, but another observer will see the second gun fire first. And this is after taking into account the finite travel speed of light... there is no actual order of two space-like separated events!
So then, it actually doesn't matter which event occured first, since the distance between them is so great that they are causally disconnected (one can't influence the other) due to the cosmic speed limit?
But try convincing the guy flying past at some large fraction of c...
So which is first is observer dependent - however, it doesn't matter which is first because neither influences each other, and, both observers are right?
I think a lesson in hyperbolic geometry is in order to explain this well, but it may have to wait until later today...
Please do as I have many questions, and I left no tac on your seat - so sit down, have some coffee and relax.
Thanks again,
- Oni

This message is a reply to:
 Message 68 by cavediver, posted 11-04-2009 10:54 AM cavediver has replied

Replies to this message:
 Message 72 by cavediver, posted 11-04-2009 7:00 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 71 of 81 (534046)
11-04-2009 3:04 PM
Reply to: Message 69 by Perdition
11-04-2009 11:12 AM


Re: Sitting Patiently
But I think I saw that Onifre kid leave a tack on your chair.
I wish I still was a kid! lol
But thanks for the compliment old-timer.
- Oni

This message is a reply to:
 Message 69 by Perdition, posted 11-04-2009 11:12 AM Perdition has not replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 75 of 81 (534094)
11-04-2009 11:17 PM
Reply to: Message 72 by cavediver
11-04-2009 7:00 PM


Re: Spacetime
Neither occured first
Sweeeet! I got it ... I got it, there is no such thing as first.
Oni writes:
since the distance between them is so great that they are causally disconnected (one can't influence the other) due to the cosmic speed limit?
cavediver writes:
Exactly!
Sweeet again!
But be careful not to trivialise this point about the 'speed limit' - c is not a speed limit in any real sense. At c you arrive at your destination in zero time. That's not a limit. It's a breakdown of this concept you think of as speed.
Like a photon, which experiences no time - It travels at c relative to us but relative to the photon it is not moving at any speed?
Notice that the 4d interval has not changed:
The same for everyone
And this is basically a length (Lorentz) contraction that finds "gamma"?
That's a start. Does that make any sense at all?
It does, it really does ... please continue when you have more time.
- Oni

This message is a reply to:
 Message 72 by cavediver, posted 11-04-2009 7:00 PM cavediver has replied

Replies to this message:
 Message 76 by cavediver, posted 11-05-2009 4:37 PM onifre has replied

  
onifre
Member (Idle past 2941 days)
Posts: 4854
From: Dark Side of the Moon
Joined: 02-20-2008


Message 80 of 81 (534589)
11-09-2009 4:24 PM
Reply to: Message 76 by cavediver
11-05-2009 4:37 PM


Re: Spacetime
Well, it is both length contraction and time dilation in one
Right...
quote:
But our traveller at 0.8c sees something different - he sees the distance as 0 lyrs and his journey time as 3 yrs (why 0 distance? If he does nothing, he will simply arrive at P2 simply by letting time pass - his velocity has rotated his coordinates so that Alpha C (P2) now lies directly in his future.)
I understand why he sees 0 distance (because he's just experiencing time), and how the spacetime interval is preserved.
Finally, what about a null or light-like interval? Now on Earth, and 4yrs time on Alpha C. Interval is
And thus the two do not influence each other...
However, do you mind breaking this down again:
Hmmm, if we perform LTs, the 4lyrs and 3 yrs will be transformed to other values but the (imaginary) length will be preserved. So LTs cannot take a time-like interval (+ve squared norm) into a space-like interval (-ve squared norm). Have we just shown that there is a speed limit???
I don't know exactly what you man by "LTs cannot take a time-like interval into a space-like interval" ... I think I do but I don't want to mislead myself.
Thanks again cavediver,
- Oni

This message is a reply to:
 Message 76 by cavediver, posted 11-05-2009 4:37 PM cavediver has not replied

  
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