Relativity - Oh dear, here we go again!

[robinson]

Now I'm sure somebody will try to nitpick the time thing to death. Have at it!

But what about light? Limited by the speed of light, light can't go faster, no matter how much motion is involved. You can radiate light from a source traveling almost the speed of light, and it won't go faster than light.

Which is really easy to understand, from the point of view of the light source, moving at almost the speed of light, it isn't moving. Remember, all motion is relative. We can say the light source is moving at a very high speed, but that is from our viewpoint. The light source is standing still, from the point of view of the light source. So light radiates from this object at the speed of light.

It is the observer elsewhere that it is moving.

Which is really interesting. If you are in front of the moving object, so it is approaching you very fast, the light, at the speed of light, is just light approaching at the speed of light.

So how can that be? We have this tremendous energy, this motion, and it doesn't matter? Well, yes it does matter. The light is Doppler shifted to a higher frequency, which neatly keeps the Universe and the conservation of energy all happy.

So instead of visible light, that fast moving object appears to be radiating x-rays, or higher energy rays. Depends on the relative speed.

An observer behind our light emitting object experiences radio waves, or lower, depending on the velocity difference. So now light, isn't really what we think it is, any more than time is. Light depends on our relation to the source. Speed away from an X-ray source fast enough, and it becomes visible light.

Speed towards a star, and it becomes invisible to the eye, all ultraviolet and x-rays or worse. So now light isn't what it seems, it depends on the observer as well.

Of course we can't really speed around the Universe at those speeds. But we know that some things can go really fast. Little tiny particles can go almost the speed of light. Which brings us back to time. If a little tiny particle that lasts for just a really tiny amount of time, is accelerated really fast, it lives longer, at least to us. (we can actually do this, it isn't just theory)

Does it last longer from it's point of view? No. You can't change time for a particle, just like you can't change time for a person. But if you speed something up, it seems to those not moving, relatively speaking, to last longer. Time slows down, from the non moving observers point of view. I think.

It is really complicated. Sort of.

I think it is all relative.

 

[sol invictus]

Sure, but that event can’t occur in isolation from the rest of existence. If you’re going to theoretically freeze time in the exact centre of Red Square, it also has to apply to the rest of the universe at the same time. In other words, I don’t see that an event can be just local, regardless that your focus might be local. So I don’t see that my use of the word event is any different than yours.

Sorry, I really don't understand what you're trying to get at. I didn't say anything about "freezing" time.

Look, you know how you can label space with a coordinate system? Like a piece of graph paper with numbers at the vertices, only three dimensional? Imagine adding one more dimension (time) and labeling that one too. So now you have a four dimensional space, and every point is labeled with 4 numbers - position in 3d and time. An event is a point in that space. Objects are lines in that space (because even if they aren't moving, they are still traveling forward through time). Those lines are called worldlines.

What it sounded like you were talking about is a "sheet" in or slice of that space - a 3d section defined by constant time. That's not an event - that's the entire universe at one fixed time (in some particular frame).

Incidentally, if you've been able to picture this so far, time dilation is very easy to understand. You just have to know that velocity (going to another frame) makes those constant time surfaces tilt. If you think about what that means for the worldline of an object, you'll see why its time is dilated.

 

[ynot]

Sorry, I really don't understand what you're trying to get at. I didn't say anything about "freezing" time.

You described an event as being ”at a particular point in time” and “at precisely 12 noon“ (post#375).

And 69dodge (post #351) “An event is an instantaneous occurrence of infinitesimal size. It can't move---moving takes time.”.

I interpret both these statements as meaning “freezing” time, or an event has no time. To put it another way, can an your Red Square event last 2 seconds?

 

[sol invictus]

You described an event as being ”at a particular point in time” and “at precisely 12 noon“ (post#375).

And 69dodge (post #351) “An event is an instantaneous occurrence of infinitesimal size. It can't move---moving takes time.”.

Right.

I interpret both these statements as meaning “freezing” time, or an event has no time.

It's just something that happens at one instant, one moment in time. It doesn't mean time "freezes". At the moment your watch hit midnight yesterday, did time freeze?

To put it another way, can an your Red Square event last 2 seconds?

Technically, no - that would be a series of events, just as something taking place over a square meter would involve a collection of spatial points (rather than just one).

 

[ynot]

Right.



It's just something that happens at one instant, one moment in time. It doesn't mean time "freezes". At the moment your watch hit midnight yesterday, did time freeze?



Technically, no - that would be a series of events, just as something taking place over a square meter would involve a collection of spatial points (rather than just one).

Can “one instant, one moment in time” exist in reality? To say they exist for an infinitely small amount of time is essentially saying they exist for no time, and therefore don’t exist. Can movement/time exist in increments?

Perhaps movement/time does have incredible small but actual increments, and everything starts and stops at an incredibly fast rate that we will never be able to observe or measure. Or am I dancing too far from the music again?

ETA - Was there an actual “moment your watch hit midnight”? If so, how long did it last for?

 

[BillyJoe]

Are you being funny?

I have to convince myself that you are trying to be.
...because it would be too sad if you weren't.

BillyJoe

 

[sol invictus]

Can “one instant, one moment in time” exist in reality?

I don't know, no one knows, no one will ever know, but that's irrelevant to this conversation. What matters is that we have a theory in which instants exist and make perfect sense, and that theory reproduces what we observe with incredible accuracy.

To say they exist for an infinitely small amount of time is essentially saying they exist for no time, and therefore don’t exist.

Why? That's just not true.

Look - have you taken any math at all? If so, you must be perfectly comfortable speaking about points in space. In physics, particles (real particles, with mass, energy, etc.) can be represented as points, literally points - with no length, width, or breadth - and they exist happily (at least in the theory), interact, and model the world very very well. This is no different.

 

[Fredrik]

When you started with

Nice try, but...

I expected the rest to be ridiculous, but later in that post you showed that you came to the right conclusion eventually:

For all practical purposes, the moving clock/twin is experiencing time speeding up, watching the earth move.

So now time isn't how long it takes the earth to spin once, or anything really, it is what you measure it to be, based on your position and speed, relative to the earth.

Good for you.

Is the concept of "real" time even valid?

It isn't.

If time is different for different clocks/observers, depending on where they are, and how fast they are moving, what does that mean?

It means that space and time is much more accurately described by special relativity than by our intuition (which is based on experiences involving low speeds).

Which, if you think about it, is pretty cool.

That it is.

Now I'm sure somebody will try to nitpick the time thing to death.

What you're saying in this post is essentially correct. I wouldn't say that it's "really easy" to understand why light emitted from a light source that's moving towards us at almost the speed of light isn't moving faster than the speed of light, but at least these things are described by a theory (special relativity) that can be understood pretty well without advanced mathematics.

It is the observer elsewhere that it is moving.

This is one thing I could nitpick, but if you have understood that time isn't absolute, you have probably understood that motion isn't either.

 

[ponderingturtle]

Forget accuracy to the level of an atomic clock. You can use the moon, the earth, or the sun as time keepers. The point, which is obvious, is that the orbiting twin, or clock, experiences time in a different way.

So you are saying that if you measure your time by clocks in other reference frames you create contradictions?

And that why is that supposed to be meaningful?

 

[ponderingturtle]

It doesn't matter how you define it. The atomic clock or the rotation of the earth, both events, observed from the moving space ship, seem to go faster.

Yes and? If compared his clock to the ones on earth he could determine that his are going slower. Why do you seem to think that this creates contradictions?

So our moving twin sees the same number of rotations, or ticks of the clock, they just seem to go by faster. It doesn't matter if it is years, days, or seconds on an atomic clock, time goes faster, outside the space ship.

Yes he sees the same number of those on the clocks on earth go by, but his clock experiences fewer of them.

So they see 3,000,000 years go by, they just went quicker. 3,000,000 revolutions around the sun, or the same amount of time on a clock, it doesn't matter. Movement, and changes in gravity, cause the speed, or time, of rest of the universe to change, to that observer.

Not for him he has fewer years as measured by his own atomic clocks. As long as we build up a definition of year as being comprised of 365 days and the say being comprised of 24 hours and so on.

 

[ponderingturtle]

Sure, but that event can’t occur in isolation from the rest of existence. If you’re going to theoretically freeze time in the exact centre of Red Square, it also has to apply to the rest of the universe at the same time. In other words, I don’t see that an event can be just local, regardless that your focus might be local. So I don’t see that my use of the word event is any different than yours.

There is no universal now. Events can be seen by different observers to be occuring in different orders provided that they can not be connected by a beam of light or anything slower than it.

 

[robinson]

EM is measured by frequency. We say that EM is "this", based on the wavelength. But observation of EM depends on relative motion, so what light "is" depends on the observer. In regards to light sources from outside the proper frame.

Proper, before anyone starts asking, is what Einstein called your frame of reference. Proper is the observers space time, as opposed to relative space time.

Both space and time are relative, there is no absolute or Universal time, or space. (Remember, this is in regards to relativity). In our sensory reality, we can't detect relative effects. But with advanced scientific measurements we know relativity really happens. Tine and space change with motion.

As the link I posted earlier shows, just going up a mountain changes an atomic clock. As does taking a flight. But in our reality, based on what we know from observation, it isn't an issue.

But you start leaving the earth's gravity and going fast, and it can matter. Like the GPS example.

The Speed of Light (SOL) thing is another crazy thing to imagine, because we can't go anywhere near those speeds, it is hard to imagine the Universe speeding up, because we speed up. Which means we slow down, relative to the rest of the Universe.

So if we imagine we are a photon, traveling through space, the rest of the Universe looks really strange. I think.

 

[robinson]

I'll try to draw some up over the weekend, but if you're looking at correct diagrams, it should be pretty clear.



That will be made clear from the diagrams I intend to draw up.

Did I miss the diagrams? Are they in this thread?

 

[Ziggurat]

Did I miss the diagrams? Are they in this thread?

Yes, you missed them, and yes, they're in this thread. Post 195 and Post 290.

 

[sol invictus]

There are some in the wiki article (which looks quite good) as well.

 

[ynot]

There is no universal now. Events can be seen by different observers to be occuring in different orders provided that they can not be connected by a beam of light or anything slower than it.

There’s nothing but a universal now in terms of the reality of existence. Existence isn’t created by observation and doesn’t require observation. That the totality of existence can never be simultaneously observed (omnipresent dude aside doesn’t mean it doesn’t exist as a reality. The limitations of observation don’t define or create the limitations of reality. Perhaps you mean there’s no universal observation? If so I agree . . . but so what?

 

[ynot]

I don't know, no one knows, no one will ever know, but that's irrelevant to this conversation. What matters is that we have a theory in which instants exist and make perfect sense, and that theory reproduces what we observe with incredible accuracy.

Why? That's just not true.

Look - have you taken any math at all? If so, you must be perfectly comfortable speaking about points in space. In physics, particles (real particles, with mass, energy, etc.) can be represented as points, literally points - with no length, width, or breadth - and they exist happily (at least in the theory), interact, and model the world very very well. This is no different.

Sorry, but you appear to contradict yourself. You say that the points are literal (true to fact, not exaggerated, actual or factual) and then you say they are theoretical (not true to fact, actual or factual). Obviously a point that has “no length, width or breadth“ is only a theoretical concept that is only theoretical possible within a theoretical theory. Such a point can have no more actual existence than an invisible unicorn or god. Why is it valid to use an impossible, theoretical point to represent reality, but it’s not valid to use an invisible unicorn or god?

 

[robinson]

We're discussing special relativity in this thread. SR is a theory that describes a universe without gravity, and also without quantum effects.

Ah! I thought we were discussing reality. Now it all starts to make sense. This is a theory thread.

 

[robinson]

Yes, you missed them, and yes, they're in this thread. Post 195 and Post 290.

Those links are not to the post, but I found them. Thanks.

 

[Ziggurat]

Those links are not to the post, but I found them. Thanks.

That's odd. I tested the links myself, and they work fine for me.