Relativity - Oh dear, here we go again!

[sol invictus]

Thanks. But I can’t help wondering if such an experiments are being correctly observed and interpreted, and how much confirmation bias might be involved. Perhaps I’m too fanatical a sceptic. If the “Theory of Relativity” has been proven as an indisputable fact, why isn’t it called the “Law of Relativity“?

Well, nothing wrong with being a skeptic. And I agree that viewed from the outside, this stuff looks awfully weird. It's hard for a layperson to appreciate how much evidence there really is for it - relativity is central to many, many phenomena in physics, including everything affected by electricity or magnetism (in fact Einstein discovered it while trying to make sense of the theory of electrodynamics).

But forget all that and just think about these clock experiments. Really, how plausible is it that there is some other effect that can allow a clock to know that the plane carrying it is flying east and not west, north, or south? Or could reproduce exactly the same numbers relativity predicts? Or can explain other aspects of the same theory, like the fact that clocks on mountaintops run faster than those at the bottom? (And that's an experiment you can do for yourself, with a moderately priced pair of accurate clocks.) Or that our GPS system doesn't work if you don't take these effects into account?

 

[ponderingturtle]

You might find a dictionary handy yourself.

Noncents I will in never way subjigate my writing to the forct confirmaty of such a faith bast cistem

 

[BillyJoe]

Perhaps I’m too fanatical a sceptic.

I think "sceptic" is the wrong word.
Are you also "sceptical" of the periodic table because you are not been able to verify it yourself personally.
I think the word you are looking for is "pig-headed".

Come on, it can't be that hard to admit you have made a mistake.
You have just learnt something new.
It should be a cause for celebration!

regards,
BillyJoe

 

[robinson]

For a practical example of time and how motion effects time, consider the low earth orbit. Like the Space Shuttle often uses. At those speeds, and that height (because gravity effects time as well as motion), time passes slower than on the earth's surface.

If you use identical clocks (forget people, you will see why), and one is in low earth orbit, and the other stationary on the earth, after a hundred years, the moving clock will be about one second slower. (You see why twins would not be good)

This is scientific fact. Based on experiments. We know this is what happens to clocks.

To understand the conceptual problem, does time pass slower, or does the clock go slower, consider the same situation, except now either speed up the orbit (hard to do), or add more time.

If the orbiting clock stays in orbit for three million years, it will be a year behind the one that stayed on the ground.

The obvious question is, where did the year go? To the orbiting clock? You bring it back to earth, compare the two clocks. Yep, the orbiting clock is a year younger. According to the clock.

So, did it miss out on the earth going around the sun once? How can it be a year younger otherwise? The earth went around the sun three million times for each clock, yet the moving one shows a year less time passed. Is it a year younger? What happened? Did it travel in time?

If you use atomic clocks, or any kind of super accurate clock, you get one time, yet according to all clocks on earth, and the earth itself, the earth went around the sun 3 million times. The clock that says it only went 2,999,999 times is wrong of course. Because while the clock says there has only been 2,999,999 orbits around the sun, it actually went around the sun 3,000,000 times. We know this because it was in orbit around the earth, so there is no question how much time passed. For both the orbiting clock, as well as the ground based clock.

So how did time run slower? An observer on the space ship with the clock (assuming the observer lived 3 million years) would has watched 3 million orbits around the sun. Just like the person on the ground. Who would also note the orbiting clock went around the sun three million times.

These are the kinds of thought experiments that make you think, can you trust the clock?

And what is time?

 

[Paulhoff]

Just standing on the earth, you're time is slowed down by gravity.

Paul

 

[sol invictus]

So, did it miss out on the earth going around the sun once? How can it be a year younger otherwise? The earth went around the sun three million times for each clock, yet the moving one shows a year less time passed. Is it a year younger? What happened? Did it travel in time?

There's nothing strange about that (other than ordinary time dilation, that is). It's just that the amount of time it takes for the earth to go around the sun once is different as measured by those two clocks. Both will agree on the number of cycles.

These are the kinds of thought experiments that make you think, can you trust the clock?

Of course you can - none of this has anything to do with clocks being untrustworthy. It has nothing to do with clocks at all, really. It has to do with the nature of time.

 

[godless dave]

Clocks are interchangeable with humans? Perhaps the clock was “jet-lagged” then.

The point I was trying to make is that a clocks accuracy can (or might) be affected by the unstable environment of a flight around the world.

Which is why, when doing these experiments, physicists used atomic clocks that are not prone to such inaccuracies.

 

[Paulhoff]

Time slowing down due to moving is all mechanics.

Paul

 

[69dodge]

If you use atomic clocks, or any kind of super accurate clock, you get one time, yet according to all clocks on earth, and the earth itself, the earth went around the sun 3 million times.

The Earth didn't "go around the sun 3 million times according to clocks on Earth". It just went around the sun 3 million times. A clock doesn't tell you how many times it went around the sun. It tells you how much time has passed.

The clock that says it only went 2,999,999 times is wrong of course. Because while the clock says there has only been 2,999,999 orbits around the sun, it actually went around the sun 3,000,000 times.

The clock doesn't say that it went around the sun 2,999,999 times. It says that 2,999,999 years of time have passed for it.

We know this because it was in orbit around the earth, so there is no question how much time passed. For both the orbiting clock, as well as the ground based clock.

No. There is no question how many orbits they made about the sun. How much time passed is a different question.

So how did time run slower? An observer on the space ship with the clock (assuming the observer lived 3 million years) would has watched 3 million orbits around the sun. Just like the person on the ground. Who would also note the orbiting clock went around the sun three million times.

What's so special about the number of orbits around the sun?

Pluto orbits the sun once every 250 years or so. No one thinks this means that time runs 250 times slower on Pluto than on Earth.

These are the kinds of thought experiments that make you think, can you trust the clock?

It's not just the clock, of course. Everything else in the spaceship agrees with the clock regarding how much time has passed.

And what is time?

That's a good question. But whatever it is, the number of elapsed years shown on the readout of an atomic clock is certainly a better measure of it than the number of orbits the clock has made around the sun.

 

[robinson]

What's so special about the number of orbits around the sun?

Are you being funny?

That's a good question. But whatever it is, the number of elapsed years shown on the readout of an atomic clock is certainly a better measure of it than the number of orbits the clock has made around the sun.

Yeah, because a year has nothing to do with the earth going around the sun.

 

[ponderingturtle]

Are you being funny?



Yeah, because a year has nothing to do with the earth going around the sun.

You are being very obnoxious.

You are using two definitions of the word year to either try to confuse yourself or likely confuse others.

The main purpose of this would seem to be getting attention.

 

[sol invictus]

Yeah, because a year has nothing to do with the earth going around the sun.

You are being very obnoxious.

Don't you love it when he uses s? Apparently it's short for "I have no clue what I'm talking about, but I'm sure everyone else is wrong anyway."

Robinson, I hope your 4,000th post is higher quality than your 3,999th....

 

[robinson]

I was going to use a day for an example. It is the same problem of course. One clock says it is a day earlier than the other. But the earth spun around the same number of times for both clocks. If people lived long enough to experience the effect it would be easy to see the problem. The twin in orbit is one day younger. So where did the day go? They are missing 24 hours. But the saw the same number of rotations of the earth.

So they know the same number of days passed for them both. So the question of time comes down to a real world problem. The clock says one thing, but the obvious reality says another.

If you can't grasp the essential paradox, just ask each twin what year it is. According to the earth bound twin, it is year 3 million since the orbiting of the earth started. The twin on the space craft, looking at the clock (and calender as well at this point), would see it is the year 2,999,999. Based on the clock (the measure of time).

So what year is it for both of them? And if the orbiting twin is a year younger, as the clock says, where did that year go? He saw the same number of orbits around the sun as the earthbound twin. Yet he is a year younger.

I don't blame you if you find it hard to think about it.

Remember, the same thing happens with atomic clocks, in reality, right now. Time is slower on the space shuttle. Or at least, the clocks run slower.

Does time change? What is time?

If you want to say that the earth spinning, or the earth orbiting the sun has nothing to do with time, then what do you measure time by?

 

[sol invictus]

If you want to say that the earth spinning, or the earth orbiting the sun has nothing to do with time, then what do you measure time by?

By a clock at rest with respect to you.

Measuring time by orbits of the earth around the sun is no different than using the hands of some huge clock somewhere that everyone can see. People moving with respect to that clock will see it run slower than people at rest with respect to it, and so the "ticks" of its second hand will represent a different amount of time for different observers (which is OK, but not very convenient - for example if you tell someone your age using the number of universal clock ticks, it won't indicate very well how close to death by old age you are).

There's nothing special about the earth going around the sun, particularly if you're not stuck to the surface of the earth.

 

[69dodge]

Are you being funny?

I wasn't trying to be.

Yeah, because a year has nothing to do with the earth going around the sun.

Why do you suppose the official SI definition of the second is currently based on atomic clocks and not on the earth's movement around the sun?

The earth's movement around the sun is not as regular as you apparently think it is. And that's even without any relativistic weirdness.

 

[ponderingturtle]

I was going to use a day for an example. It is the same problem of course. One clock says it is a day earlier than the other. But the earth spun around the same number of times for both clocks. If people lived long enough to experience the effect it would be easy to see the problem. The twin in orbit is one day younger. So where did the day go? They are missing 24 hours. But the saw the same number of rotations of the earth.

So they know the same number of days passed for them both. So the question of time comes down to a real world problem. The clock says one thing, but the obvious reality says another.

Robinson first define day, are we talking 24 hours comprised of 60 minutes comprised of 60 seconds defined by duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

link

Or are we talking revolutions of the earth?

 

[Fredrik]

One clock says it is a day earlier than the other. But the earth spun around the same number of times for both clocks. If people lived long enough to experience the effect it would be easy to see the problem. The twin in orbit is one day younger. So where did the day go? They are missing 24 hours. But the saw the same number of rotations of the earth.

So they know the same number of days passed for them both. So the question of time comes down to a real world problem. The clock says one thing, but the obvious reality says another.

If you think the rotation of the Earth is just as good or even "better for keeping track of how much time has passed locally inside a space ship that's moving away from Earth at a high velocity, you're wrong. You're stuck on the pre-relativistic notion that time is absolute. If time had been absolute, then no relativistic effects would ever have been observed.

Besides, if time had been absolute, you still wouldn't have had any reason to believe that Earth is the most accurate clock in the universe.

If you can't grasp the essential paradox, just ask each twin what year it is. According to the earth bound twin, it is year 3 million since the orbiting of the earth started. The twin on the space craft, looking at the clock (and calender as well at this point), would see it is the year 2,999,999. Based on the clock (the measure of time).

So what year is it for both of them?

3 million. Yes, the astronaut twin has effectively made a trip one year into his future (and there's no way he can return).

And if the orbiting twin is a year younger, as the clock says, where did that year go?

The question doesn't quite make sense, but I'm sure you know that. The correct question would be something like "how is this possible?" and the answer would be that space and time don't have the properties they have in Newton's theory (properties that are very intuitive). Instead they have properties that closely resemble the properties of Minkowski space.

If you want to say that the earth spinning, or the earth orbiting the sun has nothing to do with time, then what do you measure time by?

Clocks. You can think of Earth as a clock if you'd like (it does have something to do with time), in two different ways actually (the two you suggested). It isn't very accurate, but for some purposes (like keeping track of how old you are) it's good enough. However, our planet viewed as a clock, only keeps track of how much time has passed in a frame where our solar system is approximately stationary. If you want to keep track of how much time has passed on a space ship, you have to put a clock on the ship, or do relativistic calculations based on its velocity.

 

[robinson]

Nice try, but obviously the earth spinning, as well as rotating around the sun IS a giant clock, as was pointed out. It doesn't have to be accurate to an atomic clock, you can see that the earth return to the same position, in relation to fixed reference points, (though 3 million years makes that impossible), but as a thought experiment it is quite valid. Way more valid than accelerating a spaceship to close to the speed of light.

Because there are actually objects that have been going around the sun for 3 million years. And there is an object rotating around the earth, like a giant clock. And the earth spins, like a giant timepiece. In fact, we use them to talk about time, all the time.

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.

But if you use an obvious giant clock, the earth, or the moon, they are not moving in the space ships orbit, so they are not effected by the speed, like a clock on board is. But you can still see them from a space ship in low earth orbit. So according to the orbiting clock, or twin, they are moving faster than they seem to the earth bound twin.

So the clock, or twin, in orbit, has a slow clock. Yet, they can see the earth spin, the earth go around the sun, so we have a wonderful paradox. The orbiting clock/twin sees time going faster, based on the clock on board. For all practical purposes, the moving clock/twin is experiencing time speeding up, watching the earth move. If we increase the velocity, (remember, this is a thought experiment, not reality), we can make it so the orbiting clock/twin goes much much faster (remember, we have really long lifetimes for our theoretical twins)

So by increasing the orbit speed, and ignoring the other problems that creates, (just like the original twin paradox thought experiment ignores acceleration and the energy involved), we can end up with the orbiting twin/clock has experienced 2,999,900 years, and the earth clock/twin shows 3,000,000 million orbits of the earth around the sun.

So the moving clock is now 100 years behind. It is the year 3 million, but according to the orbiting clock/twin, only 2,999,900 years have passed. Even when they could see all 3,000,000 years happen.

So from the orbiting clock/observer, time went faster. Obviously if we increase the velocity, we can imagine real time travel. Or reverse the motion, decrease the movement, relative to the earth, and time slows down, from the moving clocks point of view.

This is what science knows happens. Time doesn't change, (the earth goes around the sun, the earth spins, that motion does not change), but the moving observer, or clock, experiences time slowing down, or speeding up. So from this, we know time is a function of the observer, or if you will, a clock in the same motion as an observer.

So what is time? If it is variable, depending on how fast you are moving, or how much gravity you are experiencing, time is not how long something takes, it is how long you observe it takes. Which as we know, is variable, depending on your motion. 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.

Robinson first define day...
Or are we talking revolutions of the earth?

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.

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.

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.

Time on board the space ship does not change. For them. We would see their clock running slower. If they were going really fast, they are traveling in time. Actually, even if you don't go that fast time changes. According to relativity, going up a mountain changes time, as does going deep in the earth, or flying in a plane, time is changing all the time.

So what is time then? Is there really time if it changes? Is the concept of "real" time even valid? If time is different for different clocks/observers, depending on where they are, and how fast they are moving, what does that mean?

You can't slow time down, or speed it up, in the sense that you can live longer. Because your clock, where you are, doesn't change. It only changes in relation to somebody else's clock. But you can time travel, if you go really fast, in the sense that you can speed up the rest of the Universe, by moving very fast.Or, according to experiments, slow the rest of the Universe down, by reducing your speed, in relation to somebody else's clock.

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

Then there is the matter of light, which is another relative issue...

 

[ynot]

No - I don't understand what you mean, and that's certainly not how the word is used by everyone else.

An "event" is something that took place at a particular point in space and at a particular point in time. For example, a pion (an unstable particle) decayed into two photons at precisely 12 noon January 3rd 2008 at the exact center of Red Square in Moscow. That's an event.

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.

 

[ynot]

Like your scenario Robinson. My jury (and the pig in my head) are giving it serious consideration.