Time and speed and how speed impacts time

[phyti]

On 1/5/2018 at 2:08 PM, studiot said:

 

Are you sure?

I thought the innovation was that the speed of light was the same for all observers.

This is what distinguishes it from previous knowledge since in classical wave theory the wave speed depends upon the medium and is independent of the emitter.

Light propagation ls a specific instance of a physical process, and would be included in the 1st postulate.

A reference frame is a location common to a set of measurements.

An anaut in space, with a clock and laser qualifies as a frame of reference.

 

[studiot]

57 minutes ago, phyti said:

Light propagation ls a specific instance of a physical process, and would be included in the 1st postulate.

A reference frame is a location common to a set of measurements.

An anaut in space, with a clock and laser qualifies as a frame of reference.

 

What does that have to do with my comment on your post?

On 05/01/2018 at 7:08 PM, studiot said:

 

Are you sure?

I thought the innovation was that the speed of light was the same for all observers.

This is what distinguishes it from previous knowledge since in classical wave theory the wave speed depends upon the medium and is independent of the emitter.

 

[Strange]

44 minutes ago, studiot said:

What does that have to do with my comment on your post?

"A reference frame is a location common to a set of measurements" == an observer.

[swansont]

2 hours ago, phyti said:

Light propagation ls a specific instance of a physical process, and would be included in the 1st postulate.

A reference frame is a location common to a set of measurements.

An inertial reference frame is comprised of all points at rest with respect to that location. It's not one place.

[studiot]

1 hour ago, Strange said:

"A reference frame is a location common to a set of measurements" == an observer.

 

 

If you would like to go back and read all of what I said you would surely see that I was commenting upon an statement by phyti concerning the substance of Einstein's second postulate.

I cannot imagine that Einstein would postulate something that was already known.

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Posted Friday at 07:08 PM

On ‎1‎/‎5‎/‎2018 at 6:39 PM, phyti said:

Then he adds a second postulate, 'the propagation speed of light is constant and independent of the emitter for all inertial frames'.

Studiot

Are you sure?

I thought the innovation was that the speed of light was the same for all observers.

This is what distinguishes it from previous knowledge since in classical wave theory the wave speed depends upon the medium and is independent of the emitter.

 

For example a jet fighter emits sound, but it does not matter whether the jet is travelling  subsonically or supersonically, it makes no difference to the speed of sound in the air.

A moving observer will observe a different speed for the sound.

The breakthrough postulation was that this is not the case with light, but that any observer, moving or not, would observe the same speed for light.

[Eise]

12 hours ago, studiot said:

I thought the innovation was that the speed of light was the same for all observers.

This is what distinguishes it from previous knowledge since in classical wave theory the wave speed depends upon the medium and is independent of the emitter.

Well, I think it is best to let Einstein speak for himself:

Quote

1. The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.
2. Any ray of light moves in the “stationary” system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body.

So in the second postulate he really is referring to the emitter only. I assume this excludes two (logical) possible scenarios:

1. Light is moving in a medium, like sound. A jet close to the velocity of sound will 'see' the sound moving slower from him in the direction of his flight.
2. If light exists of particles (material) the velocity of the emitter should be added.

I found it always interesting that in popular explanations usually the observer is considered, not the emitter. Wonder why. Because it is easier to explain?

[Estranged]

I'm sorry y'all, this thread was driving me crazy and it seemed healthy to just ignore it. I'll get back to it one day. I do believe that the questions I'm asking are important. 

On 1/2/2018 at 4:39 AM, interested said:

I asked a question about how time is affected by gravity or acceleration, no one answered so having googled it, I will have a bash myself, but may have confused myself somewhat. 

A fundamental result in Special Relativety is that a clock along an accelerated world line through two events in space time records less elapsed time between those events than a clock along an unaccelerated world line through the same two events.

Since, in this case, an accelerated clock and an unaccelerated clock are co-located at two different events, the two clocks can be directly compared and, in this case, the time dilation is absolute - does the accelerated clock tick faster than the unaccelerated clock ?????? Is time slower in space?????????????

The muon decay mentioned by Mordred is an example of the above. The muon experiences no acceleration ie is in free fall as it enters the earths atmosphere and it experiences a slowing down of time relative to observers on the ground. Quantum excitations not being accelerated by gravity or any other force last longer. This must alsoi apply to all Quantum fluctuations and excitations in space, not experiencing acceleration.

Does a Photon of light travelling at c experience time, No it doesnt https://en.wikipedia.org/wiki/Time_dilation

If a person leaves earth at 0.7c for 20  years before returning, how much as said person aged when acceleration and deceleration are taken into account. The above examples ignore acceleration?

Viewing the above as a bungey jump as your speed increases to earth time slows, like a muon, as the elastic takes up the tension you decelerate and experience an increase in the speed of time, if the rope breaks your life ends like the muon, if not you are accelerated back up towards the crane at what feels like a much faster rate than you descended, until you reach the height of your climb when you start on the way back down again.

For the observer on the ground time is not affected for the person doing the bungy jump they experience a decrease in the speed of time followed by an acceleration as the rope becomes taught again.

PS I do not recomend bungey jumping, I dont think it is good for the brain cells having so much blood rush into your head at once.

Edit Biological systems experiencing higher levels of gravity will have higher masses and will have to work harder, and use more energy, joints will ware out faster, and they will experience time ticking at a faster/slower ???? rate. It will feel longer due to the extra work that will have to be done, but may in fact be faster.

This is the most interesting post I've read. I'll have to read it another 20 or so times before I can begin to understand it though. 

[StringJunky]

9 minutes ago, Estranged said:

I'm sorry y'all, this thread was driving me crazy and it seemed healthy to just ignore it. I'll get back to it one day. I do believe that the questions I'm asking are important. 

It's not an easy subject. Half the problem is trying to relate it to commonsense when you need to let go of it because it's not in the realm of everyday experience. Much of physics beyond the Newtonian world we experience is counterintuitive.

[swansont]

58 minutes ago, Eise said:

I found it always interesting that in popular explanations usually the observer is considered, not the emitter. Wonder why. Because it is easier to explain?

The observer can always assume s/he is at rest.

[studiot]

1 hour ago, Eise said:

Well, I think it is best to let Einstein speak for himself:

So in the second postulate he really is referring to the emitter only. I assume this excludes two (logical) possible scenarios:

1. Light is moving in a medium, like sound. A jet close to the velocity of sound will 'see' the sound moving slower from him in the direction of his flight.
2. If light exists of particles (material) the velocity of the emitter should be added.

I found it always interesting that in popular explanations usually the observer is considered, not the emitter. Wonder why. Because it is easier to explain?

Sure let the Man speak.

So on page 8 of the document you link to he says

Quote

Einstein

We now have to prove that any ray of light, measured in the moving system,
is propagated with the velocity c, if, as we have assumed, this is the case in the
stationary system; for we have not as yet furnished the proof that the principle
of the constancy of the velocity of light is compatible with the principle of
relativity.

He then goes on to prove the methematics.

 

So what is this a statement of if not to say that the c is independent of the observer?

 

It may be that Einstein's original words said this in a roundabout way (I have not read the document you refer to before) and that attributing this to the observer is a modern distillation.

So thank you for providing the link where I could get the pdf.
The only document of his I have is the Lawson translation English translation of his Princeton book 'Relativity' 1957 version (original English  translation 1920)

Where he follows much the same path.

 

You haven't addressed my question why would he not address observers in some way since it was already known that the velocity of waves were independent of the emitters and this was published before the quantum duality was proposed, so the prevailing theory of light was still Young's wave theory.

 

 

[Strange]

1 hour ago, Estranged said:

This is the most interesting post I've read. I'll have to read it another 20 or so times before I can begin to understand it though. 

I wouldn't bother. It is a mash-mash of facts, misunderstandings and fiction.

Edited January 8, 2018 by Strange

[Janus]

On 12/31/2017 at 1:42 PM, geordief said:

How much of a difference will it make to the time discrepancies if the accelerations required for departure,turnaround and homecoming are maximized or minimized?

Okay lets consider the following problem:

You are traveling to a star 20 ly distant and returning.

First we'll assume a reasonable acceleration of 9.8 m/sec^2 (as felt by our traveler), and assume that they start the trip with this acceleration for 2 years as measured by the Earth.

This will get them up to  ~0.9c relative to the Earth, and They will have traveled ~1.25 ly from Earth. 

The crew of the ship will have aged 1.42 years while under acceleration.

The ship now coasts at 0.9c until it is 1.25 ly from the destination star.  This will take ~19.44 years by the Earth clock, during which the crew ages ~8.47 years. 

The ship then decelerates(at 1g according to the crew) until it reaches the star, this takes another 2 years Earth time and 1.42 years ship time. It continues firing its engines to start the trip home, taking 2 Earth years and 1.42 ship years to reach 0.9c again.

1.25 ly from Earth, it starts braking again, finally coming to a rest with respect to the Earth 2 Earth years later.

Total Earth time for the trip = 4*2+2*19.44 = 46.88 yrs

Total ship time for the trip  = 4*1.42+8.47 = 22.62 yrs,  24.26 years less or ~48% of the Earth time.

Eliminating acceleration periods and going straight to 0.9c for both legs gives

Total Earth time = 44.44 years

total Ship time = 19.37 years, ~25 years less or ~43.6% of the Earth time.

 

[geordief]

1 hour ago, Janus said:

Okay lets consider the following problem:

You are traveling to a star 20 ly distant and returning.

First we'll assume a reasonable acceleration of 9.8 m/sec^2 (as felt by our traveler), and assume that they start the trip with this acceleration for 2 years as measured by the Earth.

This will get them up to  ~0.9c relative to the Earth, and They will have traveled ~1.25 ly from Earth. 

The crew of the ship will have aged 1.42 years while under acceleration.

The ship now coasts at 0.9c until it is 1.25 ly from the destination star.  This will take ~19.44 years by the Earth clock, during which the crew ages ~8.47 years. 

The ship then decelerates(at 1g according to the crew) until it reaches the star, this takes another 2 years Earth time and 1.42 years ship time. It continues firing its engines to start the trip home, taking 2 Earth years and 1.42 ship years to reach 0.9c again.

1.25 ly from Earth, it starts braking again, finally coming to a rest with respect to the Earth 2 Earth years later.

Total Earth time for the trip = 4*2+2*19.44 = 46.88 yrs

Total ship time for the trip  = 4*1.42+8.47 = 22.62 yrs,  24.26 years less or ~48% of the Earth time.

Eliminating acceleration periods and going straight to 0.9c for both legs gives

Total Earth time = 44.44 years

total Ship time = 19.37 years, ~25 years less or ~43.6% of the Earth time.

 

The huge physical demands of going straight to  or extremely quickly to .9c  seem largely unrelated to the fairly minor changes in overall time discrepancies and seems to bear out what I have heard being said that acceleration per se is not a cause of time dilation -relative motion is.

That is my gut reaction

 

[Estranged]

A proposal: Time is actually a constant even though we may not ever be able to measure it with complete accuracy. Isn't it reasonable to believe that even with all the fancy clocks we can't really measure time as a constant? There's too many variables. Nothing is stationary. Relative station cannot be reasonably figured. We have human weaknesses. Measuring time is certainly one. The clocks on the planes going around the Earth, to think that they could account for all variables, and to think they could account for aging, seems absurd. 

Edited January 8, 2018 by Estranged

[beecee]

5 minutes ago, Estranged said:

A proposal: Time is actually a constant even though we may not ever be able to measure it with complete accuracy. Isn't it reasonable to believe that even with all the fancy clocks we can't really measure time as a constant? There's too many variables. Nothing is stationary. Relative station cannot be reasonable figured. We have human weaknesses. Measuring time is certainly one. The clocks on the planes going around the Earth, to think that they could account for all variables seems absurd. 

Your first mistake is your "argument from incredulity" fallacy.

Your second mistake is that as you have been shown now many times, space and time are actually variable and it is the speed of light which is constant. This is now well and truly beyond any reasonable doubt, and has been confirmed many times and continues to be confirmed every day.

[Eise]

17 hours ago, studiot said:

So what is this a statement of if not to say that the c is independent of the observer?

Well, I think the 2. postulate is clear: it is about the emitter of light. The location you cite seems the derivation to me, that it also means that the velocity of light is the same for all observers.

17 hours ago, studiot said:

You haven't addressed my question why would he not address observers in some way since it was already known that the velocity of waves were independent of the emitters and this was published before the quantum duality was proposed, so the prevailing theory of light was still Young's wave theory.

I am over-asked. (Is that English?). I assume Einstein wanted to start with postulates as close to the normal ideas of physics in his time. Independence from the emitter must not have been a problem, as waves propagate with a fixed velocity in it medium. But how he gets at independence of the observer is not clear to me. 

 

[Strange]

20 hours ago, studiot said:

You haven't addressed my question why would he not address observers in some way since it was already known that the velocity of waves were independent of the emitters and this was published before the quantum duality was proposed, so the prevailing theory of light was still Young's wave theory.

He does, indirectly. When he says "emitted by a stationary or by a moving body" we know (from Galilean relativity) that this can also mean a stationary emitter with the observer moving relative to it or not.

Nowadays, the postulates are often expressed in terms of the observer. And that sometimes leads people to ask "does it depend on the motion of the source?" So, without being excessively wordy, it seems you can't win either way.

[interested]

23 hours ago, Estranged said:

This is the most interesting post I've read. I'll have to read it another 20 or so times before I can begin to understand it though. 

Thanks I was asking questions like you, BUT that post of mine has some errors, the link I posted https://en.wikipedia.org/wiki/Time_dilation is I think very good, and worth reading several times. The bungy analogy needs modifying however. 

Time slows down on large planets compared with space, where time normally ticks faster unless you are moving, you will also be heavier on larger planets, in a Black Hole time could even stop. Moving through space slows time down, but in every day life even for astronauts the record achieved so far is  0.02s http://www.huffingtonpost.co.uk/2013/10/23/sergei-krikalev-time-travel_n_4147793.html after months in space, orbitting the earth. So its not really worth worrying about, unless you are navigating by GPS where time dilation effects experienced by GPS satellites are important, and need to be taken into account.

 

On 1/7/2018 at 9:05 PM, studiot said:

thought the innovation was that the speed of light was the same for all observers.

Would extra spacial dimensions help explain how a photon appears to travel at the same speed for all observers. 

[Strange]

38 minutes ago, interested said:

Would extra spacial dimensions help explain how a photon appears to travel at the same speed for all observers. 

Why would it? 

[Janus]

3 hours ago, interested said:

 

Time slows down on large planets compared with space, where time normally ticks faster unless you are moving, you will also be heavier on larger planets,

 

This is not always the case.   For example, on the surface of Uranus a clock would tick slower than it would on the surface of the Earth, yet you would weigh less on the surface of Uranus than you would on the surface of the Earth.  Gravitational time dilation is not tied to the local acceleration due to gravity.

[Phi for All]

8 hours ago, interested said:

Would extra spacial dimensions help explain how a photon appears to travel at the same speed for all observers. 

!

Moderator Note

This is a hijack. Start a new thread if you want to explore this. 

 

[studiot]

14 hours ago, Eise said:

Well, I think the 2. postulate is clear: it is about the emitter of light. The location you cite seems the derivation to me, that it also means that the velocity of light is the same for all observers.

 

I'm sorry to say that neither the wider physics community nor I interpret Einstein's writing in such a narrow way.

 

You are sadly missing both my and his major and most important points about his breakthrough.

 

 

 

 

 

 

[Eise]

11 hours ago, studiot said:

I'm sorry to say that neither the wider physics community nor I interpret Einstein's writing in such a narrow way.

Sorry, I am just looking at the text. Einstein very clearly says:

Quote

The following reflexions are based on the principle of relativity and on the principle of the constancy of the velocity of light. These two principles we define as follows:—

And these are the principles:

Quote

1. The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.
2. Any ray of light moves in the “stationary” system of co-ordinates with the determined velocity c, whether the ray be emitted by a stationary or by a moving body.

From these principles he derives the rest, including the independence of the velocity of light for the observer. I assume he could have done it the other way round: take observer-independence, and from there derive emitter-independence. But he clearly does it the other way round. 

11 hours ago, studiot said:

You are sadly missing both my and his major and most important points about his breakthrough.

No idea why you think that. When from both postulates follows that for every emitter and observer the velocity of light is c, then it is clear that in this article special relativity 'is born'. 

 

[phyti]

studiot;

I thought the innovation was that the speed of light was the same for all observers.

Einstein papers are available here

After introducing the magnet-wire example, Einstein states;

"Examples of this sort, together with the unsuccessful attempts to discover any motion of the earth relatively to the ``light medium,'' suggest that the phenomena of electrodynamics as well as of mechanics possess no properties corresponding to the idea of absolute rest. They suggest rather that, as has already been shown to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good. We will raise this conjecture (the purport of which will hereafter be called the ``Principle of Relativity'') to the status of a postulate, and also introduce another postulate, which is only apparently irreconcilable with the former, namely, that light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body."

The 'principle of relativity' is the core idea, light propagation is secondary. The underlined statement refers to an absolute value for light speed being 'out of place' with the 'principle'.

This is what distinguishes it from previous knowledge since in classical wave theory the wave speed depends upon the medium and is independent of the emitter.

Einstein continues;

"The introduction of a ``luminiferous ether'' will prove to be superfluous inasmuch as the view here to be developed will not require an ``absolutely stationary space'' provided with special properties, nor assign a velocity-vector to a point of the empty space in which electromagnetic processes take place."

Before the 1600's, light speed was thought to be instantaneous. The wave theory and particle theory kept exchanging places for the preferred theory until the evidence accumulated in favor of the discrete quanta of energy. Planck defined it to calculate 'black body' radiation. Einstein used it in his paper on the 'photoelectric effect'. Evidence for light speed being independent of the emitter was verified from many varied sources.

 

On 1/8/2018 at 2:48 PM, geordief said:

The huge physical demands of going straight to  or extremely quickly to .9c  seem largely unrelated to the fairly minor changes in overall time discrepancies and seems to bear out what I have heard being said that acceleration per se is not a cause of time dilation -relative motion is.

That is my gut reaction

 

This paper specifically shows acceleration is not a causal factor in time dilation, but a means to an end, being to increse speed.

https://app.box.com/s/1vw14m394hdcqhjv861b9s246w3gp0lk
 

[interested]

On 1/9/2018 at 2:37 PM, Janus said:

This is not always the case.   For example, on the surface of Uranus a clock would tick slower than it would on the surface of the Earth, yet you would weigh less on the surface of Uranus than you would on the surface of the Earth.  Gravitational time dilation is not tied to the local acceleration due to gravity.

 

Is that due to the movement through space of Uranus, or its spin rate or a mixture both or something else.

Edited January 10, 2018 by interested