Quite often I disagree with your continued permission to post on here.
What time is it?
- Thread starter Motor Daddy
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Motor Daddy
Valued Senior Member
Stick to the task at hand, do you agree it is 12:00:00 at the front and rear of the plane?
spidergoat
Valued Senior Member
Time is established by popular consensus. It's the same time within the entire time zone.
However, if you had two very accurate clocks, synchronized on the ground, and one was in the air while the other was on the ground, they would theoretically show slightly different times because of the velocity of the plane.
Light has a definite speed, so it would take some amount of time to travel between any two points in space larger than a plank length apart.
Ooh, I sense an oncoming case of the old "relativity is just light propagation delay" mistake that crackpots are prone to.
Fraggle Rocker
Staff member
When you say, "what time is it?" or, "the time is..." you are talking about the official time as defined by the government of the jurisdiction in which you're located. This is related to and dependent on sidereal time, solar time, or whatever scientific term you prefer, but it is not the same as that time.
The time, as we use the term in vernacular language, at any instant, is the same throughout a time zone. Time zones are segments approximately one twenty-fourth of the earth's surface, but emphasis is on the word "approximately." They are defined politically and in many cases encompass locations that are as much as one hour off from their midpoint. The International Date Line wanders all over the Pacific Ocean and is the most famous exception to the rule.
During most of its flight an airplane will be entirely within one or another time zone. At the speed of a commercial jetliner, it will take a small fraction of a second to cross the boundary of a time zone, so if someone asks you "what time is it?" at precisely that moment, by the time you answer the question the entire plane will be securely in a single zone.
I don't know if anyone has bothered to address this question in the rules of aviation, but if I had written them I would dictate that "the time" on any part of an airplane is the time at the location of the captain's clock.
The time, as we use the term in vernacular language, at any instant, is the same throughout a time zone. Time zones are segments approximately one twenty-fourth of the earth's surface, but emphasis is on the word "approximately." They are defined politically and in many cases encompass locations that are as much as one hour off from their midpoint. The International Date Line wanders all over the Pacific Ocean and is the most famous exception to the rule.
During most of its flight an airplane will be entirely within one or another time zone. At the speed of a commercial jetliner, it will take a small fraction of a second to cross the boundary of a time zone, so if someone asks you "what time is it?" at precisely that moment, by the time you answer the question the entire plane will be securely in a single zone.
I don't know if anyone has bothered to address this question in the rules of aviation, but if I had written them I would dictate that "the time" on any part of an airplane is the time at the location of the captain's clock.
Motor Daddy
Valued Senior Member
The actual time it is really doesn't matter. The main concept I'm getting at is that, does everyone agree that it's the same time at the front, midpoint, and rear of the plane? Staying in one particular timezone alleviates any timezone problems. It's not a trick question.
Right, because it's arbitrary.
Everyone can agree, so they do. That's what standards are for.
Next question:
How can you tell whether a clock at the front reads the same time as a clock at the back?
spidergoat
Valued Senior Member
It depends on if the airplane is climbing or decending.
Motor Daddy
Valued Senior Member
Very carefully.
If you are at the midpoint of the plane with a single switch, which activates a light signal with a timestamp from each end, the switch is activated and the timestamped signals are sent simultaneously towards the midpoint. Knowing the fact that light always travels at c, and the midpoint is an equal distance away from each transmitter, the midpoint can timestamp the received signals and calculations can be done, and the velocity of the plane (if any) can also be known.
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Motor Daddy
Valued Senior Member
It's staying the same distance away from the center of the Earth at all times, of course.
spidergoat
Valued Senior Member
Then it depends on whether the passenger is tall or short.
Fraggle Rocker already addressed this. Its clear to everyone this is just you trying to get someone to say "It's the same time" and then you jump in with "Aha! So you admit that simultaneity in relativity is wrong!"
The person at the front of the plane will give the same verbal reply as the person at the back when asked but this is because people reply with approximate times, like "Twelve noon" when really its a few minutes after. The relativistic effects due to the position and motion of the people on the plane relative to the ground they are flying over are too subtle to be something noticed in everyday experience and thus in order to even measure them you'd need to have a much more precise definition of 'time' than just what time zone you're in. You'd have to ask questions like "How do we sync our clocks?" and "What order do you see events occur?" to each person on the plane (and perhaps another on the ground). Its only when you get down to micro and nano second accuracy would the people on the plane find they have different views on the temporal structure of sequences of events.
Given its clear what you're attempting to do with this line of questioning its clear that you've conflated the layperson motion of "What time is it" and "When did that event occur?" or people agreeing to meet or do something at a given (approximate) time with the much more precise and subtle things in relativity. Two people verbally communicating down along a plane will introduce errors due to an inability to detect nanosecond variations in phenomena which mean that in the context of them asking "What time is it, how long till we land?" then its okay to give approximate answers. In such cases 'approximate' means to the nearest 5 minutes, as people don't do timings to the nearest nanosecond.
MD, buy yourself an introductory book on special relativity as its clear to everyone here you lack any grasp in even the underlying concepts, never mind the details.
spidergoat
Valued Senior Member
What if we just assume everyone in the airplane is wearing a perfectly accurate atomic wristwatch synchronized before take off with one on the ground?
Very carefully.
If you are at the midpoint of the plane with a single switch, which activates a light signal with a timestamp from each end, the switch is activated and the timestamped signals are sent simultaneously towards the midpoint. Knowing the fact that light always travels at c, and the midpoint is an equal distance away from each transmitter, the midpoint can timestamp the received signals and calculations can be done, and the velocity of the plane (if any) can also be known.
You seem to be either answering a different question, or not spelling out what you're thinking.
How do the ends of the plane know when the switch is activated? I'm guessing by a light signal?
So, how do the retuned timestamps tell you whether the clock at the front reads the same time as the clock at the back? I'm guessing you're also considering the time at which the signals are received.
Have you worked through the process? Have you worked out a calculation that starts from the time stamps received and when they were received, and gives you:
1) The time difference (if any) between the front and rear clocks
2) The speed of the plane
And have you allowed for time dilation and length contraction in those calculations?
(I have worked them out myself... it's a very interesting and informative exercise.)
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spidergoat
Valued Senior Member
But the velocity of the frame of reference wouldn't change the speed of light, and both signals would have the same distance to travel. What speed do you think you are measuring, the speed of the plane relative to the Earth? Or the speed of the Earth/plane combination relative to the solar system? Or the speed of the Earth/plane/solar system combination through the galaxy?
Motor Daddy
Valued Senior Member
The switch closes a circuit that activates the timestamped light signals to be sent simultaneously from each end.
The signals are stamped with the time of departure and time of arrival at the midpoint.
Given the fact that light always travels at c, and the distance between the transmitters and receiver are equal, unchanging, and known, the variance in timers can be calculated and an absolute velocity of the plane can also be calculated. These are the facts of distance and time, and can't be disputed.
Motor Daddy
Valued Senior Member
The absolute velocity of the plane in space.
Both signals only travel the same distance if the plane has an absolute zero velocity. If the plane has a velocity the light signals will each travel a different distance, and hence the light travel time will be different.
I have to ask: how do you timestamp the signals, and how long does it take each signal to arrive at the light sources when the switch is closed?Motor Daddy said:
Do the light sources have their own clocks which 'timestamp' the light signals (how do they do this, but?), and if so, how do you synchronise the clocks?
Motor Daddy
Valued Senior Member
Yes, the sources have a built-in timer and stamp the signals when they are sent. The timers from each end don't have to be in perfect sync initially, the results will show how far out of sync they are compared to the receiver's timer.
How do you "stamp" a signal if it's made of light, though? Have you thought this through?Motor Daddy said:
Don't you mean the light sources will need to be synchronized, and doesn't that just shift the problem to "when" the switch is closed?
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