Light traveling from the Sun to Earth

Originally posted by lemon lime
I'm intentionally trying to keep the parameters of this as limited as possible, to discourage arguments over other topics. It's not a surefire fail-safe, but at least it keeps me off the firing range and away from stray bullets. Or maybe not... by definition a stray bullet can end up going almost anywhere.

Oops, I almost forgot to answer your implied q ...[text shortened]... o imagine some things completely different and foreign to anyones personal experience.

Are you trying to explain a theory as to how light from distant stars did not take billons of years to be seen on earth?

The Instructor

Originally posted by RJHinds
Are you trying to explain a theory as to how light from distant stars did not take billons of years to be seen on earth?

The Instructor

I don't recall seeing a theory like that one. I stopped reading and keeping up with new theories a few years ago. New science theories seem to pop up on a regular basis, like new lines of clothing fashions. Every year there's something new. I'm not saying I agree or disagree with the theory you mentioned, because I haven't read anything about it or even heard of it.

I've basically been a hermit for a few years, going to grandkid's birthday parties and dealing with the usual old guy stuff. I've been wearing the same underwear for a few years too, but I'm not sure if there is any correlation between that and when I stopped reading science articles. It's probably time for me to get caught up on some of the new theories, and see what's happening with the ones I know about... and maybe buy some new underwear.
Maybe!!.... I'm not making any promises.

Originally posted by RJHinds
I believe it is possible for something to go faster than c. However, it would not be going backwards in time. I don't believe Einstein ever said anything about going backward in time. That is complete nonsense.

The Instructor

I believe it is possible for something to go faster than c.

On what bases? Given your complete ignorance of even basic physics and given the fact that modern physics says it is probably impossible (sorry, warp drive included! ) and given that, to date, there is not a shred of evidence that it is possible, you cannot have any possible rational reason to believe that faster than c is possible.

However, it would not be going backwards in time.

Well, that belief shows your complete ignorance of relativity.

I don't believe Einstein ever said anything about going backward in time.

Again, what is the bases of this belief? You are so totally delusional about everything. In this case, it is simply a historical fact that Einstein DID say it is theoretical possible for something to go back in time but, obviously, our science is not currently capable of doing this and may never be capable although we cannot be sure of that:

http://disinfo.com/2012/11/strange-cases-of-slippage-through-time/
“...Physicists like Albert Einstein, Michio Kaku and Stephen Hawking have all said time travel is theoretically possible; our science just can’t achieve it. ...”

That is complete nonsense.

Why is it “nonsense”? How can you be CERTAIN that is is “nonsense”? You understand nothing about physics while Einstein, who had an I.Q about three times yours, DID understand physics and HE didn't believe it was “complete nonsense”! So why should we just take the word of a moron who knows NOTHING about physics that time travel is “complete nonsense” rather than the word of a genius that understood a great deal of physics who said it IS theoretically possible? -perhaps you like to explain that to us....

Note that there are good solutions to every proposed 'paradox' of time travel that have ever been made and I can go through them on request.

Originally posted by humy

I believe it is possible for something to go faster than c.

On what bases? Given your complete ignorance of even basic physics and given the fact that modern physics says it is probably impossible (sorry, warp drive included! ) and given that, to date, there is not a shred of evidence that it is possible, you cannot have any possible rati ...[text shortened]... osed 'paradox' of time travel that have ever been made and I can go through them on request.

Einstein said an effect cannot occur before its cause. So Einstein seemed to be ruling out the possibility of traveling back in time. The Idea that one could travel back in time was developed by idiots like you that did not understand what Einstein was saying.

The Instructor

Originally posted by RJHinds
Einstein said an effect cannot occur before its cause. So Einstein seemed to be ruling out the possibility of traveling back in time. The Idea that one could travel back in time was developed by idiots like you that did not understand what Einstein was saying.

The Instructor

But of course you, in your infinite wisdom, knew ALL about what Einstein was saying. And of course Einstein HAS to be right. He couldn't be wrong, could he?

Originally posted by RJHinds
Are you trying to explain a theory as to how light from distant stars did not take billons of years to be seen on earth?

The Instructor

Light is an odd duck. My dad explained relativity to me when I was about 12 or 13 years old, and when he got to the part about light appearing to travel at the same constant speed relative to any observer I was hooked. I still can't see how that works, but it has given me a lot to think about.

The best I've been able to come up with is that light apparently enjoys its own exclusive time slot, and we can give its speed a time value of zero. Imagine a train able to run along a track with no resistance... no air resistance, no friction on the tracks, no force that can slow it down. And not even a frame of reference to make it appear it might be moving faster or slower... that's the weird part.

It's almost as though the red shift we see is light intentionally stretching itself, to insure its constant speed never appears to change. And nothing it passes seems to exert a force (or provide a frame of reference) to allow us to see it moving at any other speed. But if we say light speed is comparable to a zero passage of time, then it begins to make a bit more sense when considering how it is able to pass any object at the same constant speed, regardless of where the observer is or in what direction the observer is moving. Light always appears to be moving at the same constant speed....

relative to the observer

I think of light as having zero resistance (or zero friction) in terms of its time value. I'm not sure if this idea has any real value, but I do know theoretical physics is more or less open to ideas not firmly ensconced within established frameworks. I'm not a "real" scientist (whatever that means) but I've corresponded with a few, and most of them don't seem to have a problem with many of my ideas. Those ideas can't be too far fetched though, otherwise it's very easy to be dismissed as a hack or a crank.

It seems counter-intuitive, but I wouldn't be surprised to learn light from distant stars did not take billions of years to reach earth. My understanding of the universe keeps getting updated and refined. And sometimes I have to clear out the attic and start over again. Whoever said the more I learn the less I know knew exactly what he was talking about.

Originally posted by lemon lime
Now let's assume an imaginary observer who is able to view the entire universe, and also assume his clock is the constant. In other words, no matter what relative differences in time may be in effect throughout the universe, we are able to view everything happening (through this observer) in 'real time' according to this observers clock. The observer is a ...[text shortened]... of events in the universe can be assigned in order of time according to this observers clock.

There is no such observer. There is no way of observing the entire universe all at once and there is certainly no way of making instantaneous observations. You can assign a coordinate system and order events according to that coordinate system, but each observer is entitled to do that. If the separation of two events is greater than the difference in time between them then the order in which they happen depends on what the reference frame of the observer is. So your argument against time travel fails.

As I remember it, in classical general relativity there are no time-like loops, in the quantum theory they may be - this means that if time travel is possible you can go backwards in time of the order of the Planck time which isn't far enough to cause paradoxes.

Originally posted by RJHinds
Einstein said an effect cannot occur before its cause. So Einstein seemed to be ruling out the possibility of traveling back in time. The Idea that one could travel back in time was developed by idiots like you that did not understand what Einstein was saying.

The Instructor

Einstein said an effect cannot occur before its cause.

'cause' in which frame of reference? The SAME frame of reference as the effect or a DIFFERENT frame of reference at the effect? If Einstein said those exact words, he obviously meant the SAME frame of reference. But Einstein said and relativity actually says that the order of events can appear DIFFERENT in DIFFERENT frames of reference thus this would not rule out time travel.

So Einstein seemed to be ruling out the possibility of traveling back in time.

No, he did not “seem” to rule it out. You clearly don't understand anything he said at all.
He only ruled out time travel SPECIFICALLY by something going faster than light BUT NOT time travel by OTHER means. What about time travel via wormholes? His own theory suggested that it may be possible and he NEVER ruled out that possibility.

The Idea that one could travel back in time was developed by idiots like you that did not understand what Einstein was saying.

No. I understand what he was saying and you don't. It was geniuses like Einstein that told us the physics that show how time travel might be possible (wormholes ) and idiots like you who think they know better despite having no credentials but haven't a clue what they are talking about but still arrogantly think they know better even when scientists that understand the basic physics tell you you are wrong.

Originally posted by humy

Einstein said an effect cannot occur before its cause.

'cause' in which frame of reference? The SAME frame of reference as the effect or a DIFFERENT frame of reference at the effect? If Einstein said those exact words, he obviously meant the SAME frame of reference. But Einstein said and relativity actually says that the order of events c ...[text shortened]... know better even when scientists that understand the basic physics tell you you are wrong.

Well you know what he is doing, right? Trying (in vain) to push us in the direction that he (in vain) thinks will show us the (read, HIS) truth, that the Earth is only 6000 years old and the world wide flood really happened and the reason all those craters on the moon are cool now is they were flooded with water. SURE. It could happen🙂

Originally posted by humy

Einstein said an effect cannot occur before its cause.

'cause' in which frame of reference? The SAME frame of reference as the effect or a DIFFERENT frame of reference at the effect? If Einstein said those exact words, he obviously meant the SAME frame of reference. But Einstein said and relativity actually says that the order of events c ...[text shortened]... know better even when scientists that understand the basic physics tell you you are wrong.

No, Einstein meant any frame of reference. If one event can cause another then the two events have to have a time-like interval between them. This means that there is no frame of reference where the two causally connected events can swap over their time ordering. Cause and effect are Lorentz invariant.

Originally posted by DeepThought
There is no such observer. There is no way of observing the entire universe all at once and there is certainly no way of making instantaneous observations. You can assign a coordinate system and order events according to that coordinate system, but each observer is entitled to do that. If the separation of two events is greater than the difference in ...[text shortened]... go backwards in time of the order of the Planck time which isn't far enough to cause paradoxes.

There is no such observer.

The observer is imaginary, so I assume you mean we can't use the idea of an observer the way I used it.

There is no way of observing the entire universe all at once and there is certainly no way of making instantaneous observations.

Hence the observer is imaginary, and can only be used as a visual aid. I sense a disagreement coming, but so far we are both on the same page.

If the separation of two events is greater than the difference in time between them...

Uh oh, here it comes...

...then the order in which they happen depends on what the reference frame of the observer is. So your argument against time travel fails.

You lost me. What exactly does the separation of two events is greater than the difference in time between them mean? It appears you are saying an effect can come before a cause if the separation of two events is greater than the difference in time between them. Is that what you mean?

I don't see how any observers reference frame can determine an order of events. You said yourself that Planck time is more of a numbers game, but even if it's possible to jump back a very small distance (in time) then wouldn't all the forces that hold us together kick into reverse? Paradoxes wouldn't be the only potential problem.

Originally posted by lemon lime
Light is an odd duck. My dad explained relativity to me when I was about 12 or 13 years old, and when he got to the part about light appearing to travel at the same constant speed relative to any observer I was hooked. I still can't see how that works, but it has given me a lot to think about.

The best I've been able to come up with is that ligh aid the more I learn the less I know knew exactly what he was talking about.

I think sunhouse and humy could use a little learning to understand how little they know and perhaps they would not be so quick to dismiss the idea that the earth is thousands and not billions of years old.

The Instructor

Originally posted by DeepThought
No, Einstein meant any frame of reference. If one event can cause another then the two events have to have a time-like interval between them. This means that there is [b]no frame of reference where the two causally connected events can swap over their time ordering. Cause and effect are Lorentz invariant.[/b]

Do you agree or disagree with Einstein? It seems you were saying something else earlier. Do you think time travel into the past is or can be literally possible, or do you believe it can't happen?

Originally posted by lemon lime
Do you agree or disagree with Einstein? It seems you were saying something else earlier. Do you think time travel into the past is or can be literally possible, or do you believe it can't happen?

I wanted to avoid using symbols as maths comes out badly in these forums. Suppose in some reference frame two events happen one at coordinate x1 and time t1 and the other at coordinate x2 time t2; then the quantity dT^2 = c^2*(t2 - t1)^2 - (x2 - x1)^2, with c the speed of light, is a Lorentz invariant, meaning it has the same value in all reference frames. If c^2*(t2-t1)^2 > (x2 - x1)^2 the separation is said to be time-like, and the ordering of the events is the same for all possible observers. If c^2*(t2 - t1)^2 < (x2 - x1)^2 the separation of the events is said to be space-like and two observers in different inertial reference frames can see the events happen in different orders. This is not a problem for causality as the events cannot have caused one another as no signal could have gone between them.

This is different from time travel backwards (forwards isn't a problem). Faster than light travel would allow a signal between events with a space-like separation, so effect could precede cause in some reference frames if faster-than-light travel is allowed. With time travel between events with a time-like separation this is more stark; one could have effect preceding cause for all observers except the time traveler and all sorts of paradoxes are possible. Current thinking is that destructive interference of the time-travelers wave-function would prevent time travel backwards over anything other than time-scales of the order of the Planck time (which is tiny). So I think that time travel is probably ruled out, as is a Faster-Than-Light drive.

Originally posted by DeepThought
No, Einstein meant any frame of reference. If one event can cause another then the two events have to have a time-like interval between them. This means that there is [b]no frame of reference where the two causally connected events can swap over their time ordering. Cause and effect are Lorentz invariant.[/b]

If one event can cause another then the two events have to have a time-like interval between them.

Oh yes, you are right. Although I actually said “Einstein said and relativity actually says that the order of events can appear DIFFERENT in DIFFERENT frames of reference thus this would not rule out time travel. “
but didn't say this is still true if one of those events causes the other; but I still take your point because I erroneously implied the contrary.