Light, time, speed and senecas inevitable lack of comprehension

[Denny Crane!]

Are time and light linked?

Is it only speed that effects time? Some troubling debates have been had and I am a physics idiot.

[Justice and Mercy]

Are time and light linked?

Is it only speed that effects time? Some troubling debates have been had and I am a physics idiot.

Err... does ANYONE know? I'm not even sure we know what time really is.

But I'm truly interested.

[Denny Crane!]

Err... does ANYONE know? I'm not even sure we know what time really is.

But I'm truly interested.

Can you imagine a 6 hour debate involving vodka? I almost can't. You understand my trouble at any rate.

[ZaPPPa]

Yes
No, gravity affects time as well

Good place to start:
http://en.wikipedia.org/wiki/Introdu...ral_relativity

"About Time" is an interesting book written by Paul Davies. It can be a pretty tough read if you're not familiar with physics, but I'm afraid this subject just isn't easily explained.

[David Deas]

Are time and light linked?

Is it only speed that effects time? Some troubling debates have been had and I am a physics idiot.

Yes, they are.

A long time ago it was thought that the passage of time was constant and the speed of light was relative. But Einstein discovered that it was the speed of light that was constant, and it was the passage of time that was relative. In order to make sure the speed of light remains constant, spacetime has to warp.

Time is very arbitrary, so to speak. Its the fourth dimension of existence because just as you can rotate your X axis and turn it into Y, or your Z axis and turn it into X, or rotate any three dimensional axis into another, you can also rotate the space dimension into the time dimension. That has a lot of interesting physical consequences.

A gravitational field also influences the passage of time. Time runs more slowly for those immersed in a gravitational field. So if you were somehow able to magically hover above a black hole at the event horizon, you could potentially watch the entire history of the Universe unfold within a few moments.

[ZaPPPa]

Correct me if I'm wrong, but when you say: "the speed of light is constant", you mean in a vacuum, right?

[David Deas]

Correct me if I'm wrong, but when you say: "the speed of light is constant", you mean in a vacuum, right?

No.

I mean that every object must move at the speed of light. You, me, a particle, the planet, a photon. All of us must travel at the speed of light at all times. The key to remember is that an entity's trajectory can be either completely spacelike, completely timelike, or some mix between spacelike and timelike. But the sum of your trajectory must always equal the speed of light. No less, and certainly no more.

An object traveling at the speed of light through space has a trajectory that is completely spacelike because it is frozen in time. Thats called complete time dilation, be there such an object. An object not moving in space, be there also such an object, has a trajectory that is completely timelike. So while a photon's trajectory can be said to be completely spacelike, in that it does the speed of light through space while not traveling at all through time, your trajectory is more timelike, where you travel a corespondingly very long ways in time, but very little through space.

That is why in Relativity, two events seperated in space can never be said to be simultaneous. I can look up at the night sky and experience a burning star that is present and shining in my reference frame, but perhaps no longer there in another. The moment I experience from the star while on Earth has certainly past in the star's reference frame. But in order to move into that star's reference frame, I would have to travel through space. Traveling through space also means traveling through time. I would move from that star's past to its present.

[Spurius]

No.
I mean that every object must move at the speed of light. You, me, a particle, or a photon. All of us must do the speed of light at all times. The key to remember is that an entity's trajectory can be either completely spacelike, completely timelike, or some mix between spacelike and timelike. But the sum of your trajectory must always equal the speed of light. No less, and certainly no more.

[simplistic hat on]

So, massless particles go at lightspeed in their spacelike trajectory, and experience no time.

Eureka! Time is mass!

[Ragabash]

@David Deas

That brings up another interesting question; was there consept of time before Bing Bang (according to the theory) occured and created univerese if time is directly linked with light.

[David Deas]

From my cell phone, so bear with me.

@David Deas

That brings up another interesting question; was there consept of time before Bing Bang (according to the theory) occured and created univerese if time is directly linked with light.

Well. In order to answer that question you have to get rid of your everyday notion of time. Ball it up, throw it in the trash, and start out fresh.

Using Relativity we learned that the Universe is not a place that is coming into existence while simultaneously also obliterating out of existence. Instead, because Relativity allowed us to discover that there is no objective present anywhere in the Universe, the Universe just *is* - It has always been here and will never go anywhere. So when we talk about the Big Bang, we are simply talking about a point in existence located on the end of the line. Or at the end of the dimension. We can therefore no longer speak about any existence before the Big Bang because there is no more line left to travel further backwards on. It represents the beginning of time. Of light.

Before we give an example of Relativity in action, we'll explain length contraction because that is necessary to understand in some capacity beforehand. Whenever you accelerate an object its length will contract as acceleration increases. That is because each end of the object is following what we call geodesics. A geodesic can easily be thought of as the shortest distance between two seperate points - analogous to a straight line in spacetime. So if you could imagine a sphere with two vehicles located anywhere on the equator of the sphere, when you travel those two vehicles in a straight line (a geodesic) toward the north pole of the sphere, the vehicles will appear to converge towards one another as they finally reach the top. This is called gravity. And as they say, if you didn't know any better you'd think it was a force. Insert a metal rod in between the two vehicles as they travel towards the top of the sphere, and the rod will be squished. This is called length contraction.

A very common example given about the simultaneity of Relativity is the rod paradox, where you have two seperate observers, Alice and Bob, in relative motion meet at a common event to take a measurement on a metal rod that they both awknowledge is present. According to the rod's worldline, it will be at rest in Alice's reference frame but in motion in Bob's reference frame. So when they each take their measurement on the rod during their meeting, Alice will measure the rod longer (because it *is* longer), and Bob will measure the rod shorter (because it *is* shorter). With a diagram, we would be able to see that this result is because there actually exists two seperate three-dimensional cross sections of the same rod at once because the rod and its two seperate three-dimensional cross sections are in equal existence at all moments of its history. When Alice and Bob both took their measurements of the rod during their meeting, they succeeded at each measuring different points on the rod's worldline. They actually measured different rods, so to speak.

{EDIT} -- Removed error confusing General Relativity with Special Relativity.

Anyways.

All of this would not be possible if there were any such thing as an objective present. If there were such a thing, then Alice and Bob would both have measured the same rod at the same length at the same time. Instead, in Relativity, the metal rod is represented in your equations as an event in space-time. Exactly as the Big Bang is.

So thats how we have to think of things.

[David Deas]

@David Deas

That brings up another interesting question; was there consept of time before Bing Bang (according to the theory) occured and created univerese if time is directly linked with light.

I'd like to put kind of a note here beside my earlier explanation; the newest theories won't likely have a limitation on them as far as talking about what might have existed before the Big Bang. Quantum gravity has indeed been observed in experiment, and we think that there might have been a such thing as before the Big Bang.

String Theory is over funded, over complex and lagging behind. At this stage it looks like its just going to be a testing ground for new ideas, but thats it. Quantizing Einstein's equations seems a much more elegant solution. The latest efforts in this area have been able to reproduce Newton's laws and Einstein's equations from the ground up. So its really an exciting area of research.

[Spurius]

Time has never been oberved as a separate thing. We essentially measure only movement of 3d things, and compare that with known time-lapses of movements of other 3d things.

So we postulate a 4th dimension, since in only the observable 3, movement would not be possible.

Zeno's Paradox is very deeply linked to this fact. What's between two instances - you cannot ever 'freeze-frame' it, really. Hence all the confusion.

But separating it to a 4th is not very convincing/gratifying, since we cannot produce slices of it, simply put. It's defies observation, no tachyons on the horizon as yet.

[Chaigidel]

light and time are not related save for the fact that time is related to all things in the universe--- without the passage of time existence essentially would not be possible-- the interactions could not take place the things could not happen without the passage of this thing called time.

my personal feeling is that gravity is related to time rather than electromagnetic energetic forces-- considering that time "pools" around wells of strong gravity--- all other matter and energy simply move through existence under the passage of a universal unending moment. all time is a constant --- carried out without relativity in the universe..

relativity only applies to an observer-- time is relative to the observer this is why it may appear to be connected to light, but light is just a good way to find out how time/gravity/energy operate over great distances-- its only a measuring stick its not a necessity to time. time is not matter nor energy ( unless you want to count Entropy)-- but that is just the degradation of energy I think, the breakdown of systems.

but light and time are not the same thing and they are not dependent on one another, as far as I understand.

[Spurius]

time is not matter nor energy ( unless you want to count Entropy)

Entropy is not a thing, either - more of a statistical phenomenon, where energy conversions leave us with the energy in an ever-increasingly useless form. Like heating your room, then opening the door: retreiving that lost energy would cost more energy than it would be worth.

That's a time-dictated phenomenon, though.

Indeed, time is neither matter or energy. So, what IS it... good question. Noone really knows.

The fact we 'isolate' it to a separate 'dimension' does not make it into a materially observable phenomenon. Sure, we can work stuff, but you could navigate a flat earth with a sun revolving around it, too. Doesn't mean that approach is really 'understanding' what's going on.

[Spurius]

Fortunately, the rod was not conscious at this point in time, so no actual cruelty to rods comes into play.

One wonders what it would have reported, otherwise.

[David Deas]

Nothing. The rod has no objective length. Thats what Relativity teaches us.

You might consider the rod at rest. Maybe I might consider the rod in motion. Both of those are equally valid facts. The rod is equally at rest and in motion all the same, which means that together we know the rod possesses at least two seperate equally valid lengths all the same as far as the two of us might be concerned.

But from the rod's frame of reference, Bob would appear to be contracted. Or actually, rotated. But, contracted we'll say.

[Chaigidel]

yes but even if you were unaware of the star as it burned across the galaxy 3000000 years ago--- it still happened at the same time that the earth went around the sun that time ago-- the moment occured simultaneously our awareness of it is relative... you would not move from the stars past to the present-- you would merely be receiving the photons from the past event--- time would still carry on without fail all across the universe-- its just the great distance that makes relativity a necessary realization-- but it still only applies to observations--- time is not relative to the universe-- it is all occuring at the same time all the time.

[Silver Guard]

I mean that every object must move at the speed of light. You, me, a particle, or a photon. All of us must do the speed of light at all times. The key to remember is that an entity's trajectory can be either completely spacelike, completely timelike, or some mix between spacelike and timelike. But the sum of your trajectory must always equal the speed of light. No less, and certainly no more.

Wrong, if we were moving at the speed of light then we would have infinite mass, something physically impossible. I'd like to see where you get these 'facts' from.

[ZaPPPa]

Wrong, if we were moving at the speed of light then we would have infinite mass, something physically impossible. I'd like to see where you get these 'facts' from.

The fact that it is physically impossible does not make the theory wrong. It just means that us humans in a spaceship, for example, will never be able to become completely spacelike (reach the speed of light). And his facts come from Einstein's theories, just like yours.

I had never before seen it explained the way David did, but it makes a lot of sense to me.

time dilation in what respect?---- like that occurs on event horizon? the minute time dilation of flying in a plane?-

Does it matter? One might be negilible, which is why Newton's laws hold up, but the dilation is still there.

[David Deas]

Wrong, if we were moving at the speed of light then we would have infinite mass, something physically impossible. I'd like to see where you get these 'facts' from.

*sigh*

No one is talking about mass here, man. Or the physical possibility of traveling at c.

Lets take a look at something.

1/sqrt(1-(v^2/c^2))

Or, actually

t/sqrt(1-(v^2/c^2))

Ok. Those are a your Lorentz equations. In a couple of forms.

The Lorentz transformation equations quite plainly state that an entity's vector velocity through spacetime must *always* be c. That means the faster an object moves through space the slower it must move through time, and the slower an object moves through space the faster it must move through time.

I realize you're a noob here. And that by itself is not negative. But next time simply ask for clarification rather than being like that, please. I'll be more than happy to help. In this case, I'd ask that you to go back and read more carefully what I wrote.