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# einstein's clock tower

Tue 21 Jun, 2016 02:54 am
I recently read about the "clock tower analogy". Apparently Einstein had a brainstorm as he was passing by a local landmark, a tower with a clock at the top. As he observed it, it occurred to Einstein that if he were moving past the clock at nearly the speed of light, he would not see the hands of the clock moving because the light from the clock would be reaching him at a slower velocity than if he were travelling at a normal speed. This analogy is said to show that motion slows time. I have some difficulty with this. It seems to me that moving past the clock at nearly the speed of light would change only one's perception of time rather than time itself. Everyone back at the tower would have a much more accurate perception of the way the clock was really operating than the light-speed traveller would. So, my question, to anyone who might be able to explain it to me is, is time altered by motion or is only the perception of time altered.
That question presents me with another mystery. I understand that it has been observed that two clocks moving in directions opposite to each other at a high velocity will have slightly different readings. If this is true, then going back to the clock tower analogy, if I am moving away from the clock tower at nearly the speed of light, and the light is not reaching me as quickly as it is reaching the people near the clock, how could that possibly affect my wristwatch or any other timepiece I might have with me. It seems to me that if two clocks moving in opposite directions won't read the same, then my watch should be affected by the same principle.
I hope I have made my questions clear and understandable. Good to be here, by the way. This is my very first post.

-Llanwydd
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Type: Question • Score: 8 • Views: 9,555 • Replies: 120

roger

1
Tue 21 Jun, 2016 02:58 am
@llanwydd,
Not my kind of discussion, but I hope you get some replies.

Make yourself at home.
0 Replies

rosborne979

1
Tue 21 Jun, 2016 04:22 am
@llanwydd,
I'm not familiar with that story about how Einstein realized his famous idea. Do you remember where you heard me it?

The passing of time is also affected by motion, but the person who is moving isn't aware of his own change, only the relative changes around him.
0 Replies

maxdancona

3
Tue 21 Jun, 2016 07:24 am
@llanwydd,
You are misunderstanding relativity. You incorrectly use the term "accurate perception" when in fact, the whole point of relativity is that every point of view is equally accurate.

If you want to work through this (I am a former Physics teacher), we should start with motion. Once you understand relative motion, understanding relative time is easier.

The first step is to imagine you are on a spaceship, let's call it spaceship A, in deep space with no other planets or stars around. The only thing you can see is another spaceship. You notice that the other spaceship, called spaceship B, is getting closer.

Here is the question. Based on the information I have given you there are three ways to understand the motion between the spaceships.

1) Your spaceship is moving toward spaceship B. Spaceship B is fixed in space.

2) Your spaceship is fixed in space and spaceship B is moving towards you.

3) Both spaceships are moving towards each other.

The question is; how do you determine which of these three statements are accurate? From your point of view, your spaceship wouldn't be moving (option #1). From a person on spaceship B's perspective her spaceship isn't moving and she can see you moving (option #2).

How do you determine which of these perspectives is accurate?

TomTomBinks

1
Tue 21 Jun, 2016 08:55 am
@llanwydd,
Welcome, Llanwydd. If you stick around here you will find many brilliant and knowledgeable people. I can't answer your question very well but I'll be reading the answers!
0 Replies

fresco

2
Tue 21 Jun, 2016 10:02 am
@llanwydd,
Max is correct. There is no preferred perceptual reference frame called 'reality'. Each observer calculates 'passage of time' using the same constant figure for the speed of light relative to his own reference frame. The perception of time is in essence a psychological epiphenomenon. The departure from 'one fixed reference frame' is the crucial difference between Newtonian physics and Relativity.
0 Replies

George

2
Tue 21 Jun, 2016 11:43 am
I hope this conversation continues. I'm by no means a "science guy" and I'd
enjoy hearing this discussed in terms I can understand.
0 Replies

cicerone imposter

1
Tue 21 Jun, 2016 11:51 am

1
Tue 21 Jun, 2016 02:03 pm
@llanwydd,
I'm wondering if that observation by Einstein just gave him the idea for time being altered by movement because I don't think the analogy with light being 'slowed' reaching him is actually related to time.

If it were, he would see time speeded up when he turned back toward the clock tower. Not an expert but I think the theory goes that if you go somewhere and return at the speed of light, the clock tower time would not have changed. That's why I think Albert's thought was an inspiration rather than directly applicable to the 'time problem'.
maxdancona

1
Tue 21 Jun, 2016 02:28 pm
@cicerone imposter,

This journalist who doesn't understand anything about Physics wrote:
But, considering that Earth is moving through space, does that mean time for us is travelling faster than someone who is stationary? The answer is 'yes', and by about one second per week.

This statement is nonsensical (and false) to anyone with a basic knowledge of physics. A physicist would never use the phrase "travelling faster than someone who is stationary" because a physicist would know that the word "stationary" is problematic when talking about relativity.

I went back to read the original answer given by the gentleman called "The Physicist" and fortunately it turns out the answer given by "The Physicist" is actually a good answer (that doesn't talk about "stationary". It turns out that this is a journalist reporting what he thinks a Physicist is saying. He has no clue about what the Physicist is actually saying, so what he is reporting is ridiculously wrong.

Here is the original answer from "The Physicist" (which is actually pretty good).

Journalists screwing up science reporting is a pet peeve of mine.
cicerone imposter

1
Tue 21 Jun, 2016 05:52 pm
Fact is, everybody lives in the same time zone; earth.
Quote:
The most accurate clock ever built only loses one second every 15 billion years. Scientists have a set a new record in accurate timekeeping, creating an atomic clock that won't lose or gain a second in 15 billion years — a time span greater than the estimated age of the Universe.Apr 22, 2015
The most accurate clock ever built only loses one second every 15 ...
www.theverge.com/.../4/.../most-accurate-atomic-clock-optical-lattice-strontiu...
maxdancona

1
Tue 21 Jun, 2016 08:56 pm
@cicerone imposter,
1) This thread is about time dilation. This has absolutely nothing to do with the accuracy of clocks. Accuracy relates to how correct a clock is. In relativity, even perfect clocks (and for these problems we assume the clocks are perfect) will demonstrate time dilation.

2) How do you know that everyone lives on Earth? I suspect that there are plenty of folks who live on other planets in our Galaxy and in other Galaxies. Of course, we won't know for sure until they decide to contact us.
maxdancona

1
Tue 21 Jun, 2016 09:03 pm
@maxdancona,
I started to pose the thought experiment that I used to help my Physics students grasp the principles behind Relativity. Does anyone want to think through the question I posed?

The answer, of course, is all of the above. Option #1 and #2 and #3 are equally correct at the same time.
TomTomBinks

1
Tue 21 Jun, 2016 10:21 pm
@maxdancona,
Without another point of reference, there's no way to know.
If there was another object nearby, say an asteroid. You could judge your motion according to it. But you would first have to decide that the asteroid was the stationary object. Then, if spaceship A was stationary relative to the asteroid, you could determine that spaceship B was the one that was moving. Of course a change in perception would change the whole thing around. You could decide that spaceship B was stationary and both the asteroid and spaceship A were moving toward it at the same rate. Or even that spaceship A and the asteroid were moving toward spaceship B and simultaneously spaceship B was moving toward spaceship A and the asteroid.
maxdancona

1
Wed 22 Jun, 2016 07:42 am
@TomTomBinks,
I already gave you two points of reference TomTom, Spaceship A and Spaceship B. I fail to see how a third point of reference changes anything.
George

1
Wed 22 Jun, 2016 08:52 am
@maxdancona,
I'm going to guess that my ship is fixed in space.
What I know for sure is
* I am here
* That other ship is getting closer
TomTomBinks

1
Wed 22 Jun, 2016 09:01 am
@maxdancona,
You're right. It doesn't.
0 Replies

maxdancona

1
Wed 22 Jun, 2016 02:29 pm
@George,
But Phil, who is on the other ship, is going to guess that his ship is fixed in space.

What he knows for sure is
* He is here
* The ship that George is on is getting closer.

Foofie

1
Wed 22 Jun, 2016 03:02 pm
@maxdancona,
Can you bring in the theory of multiverses with their very likely own laws of physics? We just don't how strange all reality is (as millions of neutrinos zip right through me).

I thought that the simple fact that the speed of light is unable to change made Einstein realize that time itself had to change in some equation. This might have been why the Mad Hatter was always late for a tea party?

maxdancona

2
Wed 22 Jun, 2016 03:26 pm
@Foofie,
The theory of multiverses has nothing to do with this.

There are very well-understood and predictive equations (that have been confirmed by experiments) that describe time dilation. Time dilation is something that is fairly basic, mastered in your first couple of semesters in Physics (and some smart high school students get it).

Einsteins revelations were a little more complex than that. He was wrestling with how Maxwell's equations on electric fields would work in a relativistic universe.

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