Why two mass attracts each other?

[OnlyMe]

No, it isn't, obviously you don't know the difference. The former is accumulated time, the latter is time ratios.



I don't do physics via wiki cherry picking.

This is from one of your past links...

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/twin.html

The story is that one of a pair of twins leaves on a high speed space journey during which he travels at a large fraction of the speed of light while the other remains on the Earth. Because of time dilation, time is running more slowly in the spacecraft as seen by the earthbound twin and the traveling twin will find that the earthbound twin will be older upon return from the journey. The common question: Is this real? Would one twin really be younger?

The basic question about whether time dilation is real is settled by the muon experiment. The clear implication is that the traveling twin would indeed be younger, but the scenario is complicated by the fact that the traveling twin must be accelerated up to traveling speed, turned around, and decelerated again upon return to Earth. Accelerations are outside the realm of special relativity and require general relativity.

Despite the experimental difficulties, an experiment on a commercial airline confirms the existence of a time difference between ground observers and a reference frame moving with respect to them.​

No cherry picking I quoted the whole Hyperphysics section.., and it was you that first directed me to this particular link.

 

[Tach]

This is from one of your past links...

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/twin.html

The story is that one of a pair of twins leaves on a high speed space journey during which he travels at a large fraction of the speed of light while the other remains on the Earth. Because of time dilation, time is running more slowly in the spacecraft as seen by the earthbound twin and the traveling twin will find that the earthbound twin will be older upon return from the journey. The common question: Is this real? Would one twin really be younger?

The basic question about whether time dilation is real is settled by the muon experiment. The clear implication is that the traveling twin would indeed be younger, but the scenario is complicated by the fact that the traveling twin must be accelerated up to traveling speed, turned around, and decelerated again upon return to Earth. Accelerations are outside the realm of special relativity and require general relativity.

Despite the experimental difficulties, an experiment on a commercial airline confirms the existence of a time difference between ground observers and a reference frame moving with respect to them.​

No cherry picking I quoted the whole Hyperphysics section.., and it was you that first directed me to this particular link.

Yes, they are not exempt from being sloppy with words. Do you understand the difference between time dilation and elapsed proper time? Can you present it, briefly , like in two lines of math? What is time dilation and how do you calculate it? What is elapsed proper time and how do you calculate it?

 

[OnlyMe]

Yes, they are not exempt from being sloppy with words. Do you understand the difference between time dilation and elapsed proper time? Can you present it, briefly , like in two lines of math? What is time dilation and how do you calculate it? What is elapsed proper time and how do you calculate it?

Proper time is the time recorded by a clock in its own frame, specifically the elapsed time between events co-located with the clock.

Both twins record the elapsed proper time for the frame they are in, during the traveling twin's trip. The two times do not agree. The disagreement can be calculated where the relative velocity(s) is known throughout the traverler's trip, as a function of a Lorentz transformation... Or the average time dilation when they meet at the end and compare clocks.

The difference is the result of time dilation of the traveler's frame relative to the stay at home frame. Which twin's clock was time dilated can only be determined in the clasic basic twin paradox when they meet and compare their clocks.

 

[Tach]

Proper time is the time recorded by a clock in its own frame, specifically the elapsed time between events co-located with the clock.

I asked for math, what is the expression for proper time?

Both twins record the elapsed proper time for the frame they are in, during the traveling twin's trip. The two times do not agree. The disagreement can be calculated where the relative velocity(s) is known throughout the traverler's trip, as a function of a Lorentz transformation... Or the average time dilation when they meet at the end and compare clocks.

...and the math that expresses this is?

The difference is the result of time dilation of the traveler's frame relative to the stay at home frame.

Incorrect. The difference has a different equation, can you show it , please?

Come on, OnlyMe, physics' language is math, you pretend to be doing physics but you can't write some simple formula? How about the formula for time dilation, can you write that?

 

[Undefined]

I asked for math, what is the expression for proper time?



...and the math that expresses this is?



Incorrect. The difference has a different equation, can you show it , please?

Come on, OnlyMe, physics' language is math, you pretend to be doing physics but you can't write some simple formula? How about the formula for time dilation, can you write that?

The maths is used to predict and/or quantify the effect, not explain its cause. The effect is observed and is logically explicable according to SR theory postulates and interpretations, isn't it? Why ask for the maths in order to avoid conceding the point OnlyMe made according to SR theory?

 

[OnlyMe]

I asked for math, what is the expression for proper time?



...and the math that expresses this is?



Incorrect. The difference has a different equation, can you show it , please?

Come on, OnlyMe, physics' language is math, you pretend to be doing physics but you can't write some simple formula? How about the formula for time dilation, can you write that?

Tach, most of your posts have degraded... To the point there is no real conversation. You just keep asking others for proof you fail to provide yourself.

I initially got into this because of your laughable claim that you had proof the OWLS = TWLS. None.., none of your references supports that claim.

Stop attacking people! And offer something more than criticism, nit picking, and "because I said so!". Provide one credible reference that says your OWLS = TWLS and if the authors were unwilling to say that directly, explain it your self. No more excusing the null results with the line, "you just don't understand". No more just saying I already explained that or pointing to a link. Explain it... Prove it yourself.

You have been asking almost every one for proof of some sort, offer up some yourself.

 

[Markus Hanke]

With all due respect, Markus Hanke, I ask you naively: How do you think differing "inertial frames" got to be differing motion states? Their precursor acceleration history, that's how? You conveniently leave out acceleration when it suits, but then include it when it suits the opposite view? That is called "wanting it both ways", isn't it? Either acceleration history is automatically involved in all "differing inertial motion scenarios", or it isn't? You can't select the instances when it is included/excluded just for your convenient ignoring of that aspect when making "explanations" which "want it both ways"? So if your argument invalidates the twin experiment validity, it automatically invalidates ALL such experimental/theoretical "explanation scenarios" you use as well, yes?

Edit/: I expressly included the qualifier "non gravitational" acceleration to forestall Tach chiming in with another diversion saying "there is no gravitational acceleration in the twin scenario!" or some such evading tactic to distract from his failures. Tach is good at that pettiness tactic, as has been observed objectively by practically all here, yes?

I have no idea what you are saying here. Did I not provide a link to the definition of the term "twin paradox" ? Did you read the link ? It clearly involves a non-inertial frame, and hence acceleration. That is all I am pointing out.

I don't know what the nonsense about "wanting it both ways" is supposed to be about; I think my explanation was pretty clear. Inertial frames do not involve acceleration. Non-inertial frames do involve acceleration. They are not physically equivalent, and hence cannot be treated in the same way. That is all there is to it, nothing to do with "wanting it both ways", but everything to do with realizing the differences between the two cases.

P.S. You do realize that there are two physically distinct types of time dilation, don't you ? There is relative velocity time dilation, which is a relation between inertial clocks in relative motion, as found in SR; and there is gravitational time dilation, which is a relation between proper time readings in non-inertial frames ( or between an inertial and a non-inertial frame ), as found in GR. These are physically distinct effects, and not the same thing ! My impression is that many people on here and elsewhere do not understand this very basic fact. The time dilation experienced by an accelerated observer is of the gravitational kind, whereas the one between observers in uniform relative motion is special relativistic in nature and does not effect proper time between two given, fixed events.

 

[Markus Hanke]

Einstein's earliest references did not include twins or acceleration. It was the lack of acceleration that leads to an apparent paradox and the inclusion that leads to a solution without paradox.

Yes, I agree. From my point of view there are no paradoxes at all in relativity in general; getting a paradox in a scenario means we have done something wrong when analysing it. The "twin paradox" is a good example for this, as it illustrates what happens if we don't distinguish between inertial and non-inertial frames - they are not physically equivalent. If we eliminate the asymmetry between the frames, we can no longer get disagreements in proper time, and if we do get disagreements in proper times, then that means the frames of reference cannot be symmetric.

 

[hansda]

"Time Dilation" is 'slowing down of time' or 'slowing down of clock'?

Hansda, time dilation is not something that is measured in the same frame that the clock is in. You won't see a clock you are holding speed up or slow down, as a function of time dilation.

Time dilation is measured when comparing clocks that are in different frames, which may be frames moving at different velocities or at different distances from a significant gravitational source.

In either case time dilation does not ever result in time going backwards. Which is what I understood your reference to time reversal to mean.

"Time Dilation" as you explained above is basically 'slowing down of a clock'. Here "time" itself is not slowing down. So, "time" is remaining "invariant".

 

[hansda]

What do you mean by the word "invariant"?

invariant means dosen't change

Is a clock 'invariant'?

A "clock" is not invariant, because it is affected by gravity. So, a clock can not measure something which is invariant. If a clock can measure something, then that is not invariant. Clock can measure "proper time". So, "proper time" is not invariant.

 

[hansda]

...

Gravity is still attractive in Einstein's concept. Oh.. so you are saying gravity is repulsive too?

Always following Einstein's model...

If you are following Einstein's model, here gravity is due 'curvature of spacetime'. So, you have to explain why 'curvature of spacetime between two mass' is attractive and not repulsive.

 

[OnlyMe]

"Time Dilation" as you explained above is basically 'slowing down of a clock'. Here "time" itself is not slowing down. So, "time" is remaining "invariant".

Hansda, time is a measurement of the rate of change. Change always happens and will continue to happen for the foreseeable future. The rate at which change occurs depends on many different factors. As it relates to time.., the measurement of change, it is dependent on the frame of reference from which it is made...

While change does occur independent of being observed or measured, time requires an observation or measurement.., which is a comparison of some observed change, against an accepted standard. Clocks represent that standard. However, a comparison of the rate that two clocks record change, depends on both their relative positions in a gravitational field and/or their relative velocity with respect to each other.

Time is an abstract concept. A comparison of two rates of change, one agreed to be a standard rate. Because it is a comparrison of two rates of change, and change varies relative to many external conditions, time is not inherently invariant. But what it measures—change—happens whether it is being measured or not.

 

[OnlyMe]

A "clock" is not invariant, because it is affected by gravity. So, a clock can not measure something which is invariant. If a clock can measure something, then that is not invariant. Clock can measure "proper time". So, "proper time" is not invariant.

This is not accurate. Proper time is time as measured by a clock in its own frame of reference. In that frame of reference the clock represents the at rest frame for the measurement of the change being measured. For that measurement the clock's rate is not time dilated, it is not changing. Proper time is invariant, because it is measured by a clock collocated with the events being measured.., which is not time dilated relative to those events.

 

[OnlyMe]

If you are following Einstein's model, here gravity is due 'curvature of spacetime'. So, you have to explain why 'curvature of spacetime between two mass' is attractive and not repulsive.

The curvature of spacetime is a description of the geometry associated with gravitation, it is not an explanation of why that geometry is.

Within the context of our direct experience gravity is always attractive. Theoretically, there are conditions that would result in a repulsive graviation and there is some cosmological evidence that suggests that at very large distances gravity is either repulsive or its attrive force is no longer dominant. This leads to the need for "Dark Energy" as an explanation, for those cosmological observations.

 

[Markus Hanke]

If you are following Einstein's model, here gravity is due 'curvature of spacetime'. So, you have to explain why 'curvature of spacetime between two mass' is attractive and not repulsive.

The key concept in that regard is "geodesic deviation" :

http://en.wikipedia.org/wiki/Geodesic_deviation_equation

You will find that for two isolated bodies in space-time, their geodesics converge, i.e. the geodesic deviation is always negative. What that means is that these bodies will approach each other over time. This can be shown mathematically using the geodesic deviation equation; it is simply a consequence of the geometry of space-time.

 

[ash64449]

A "clock" is not invariant, because it is affected by gravity. So, a clock can not measure something which is invariant. If a clock can measure something, then that is not invariant. Clock can measure "proper time". So, "proper time" is not invariant.

Proper time is not invariant in Gravity.. Haven't i explained this before in my post? And do you exactly know what i was explaining through my post?

 

[ash64449]

If you are following Einstein's model, here gravity is due 'curvature of spacetime'. So, you have to explain why 'curvature of spacetime between two mass' is attractive and not repulsive.

It is because of equivalence principle. curvature is always about attractive and it cannot be repulsive..

Do you know how Einstein came to know that Gravity must bend light or gravity is itself curvature of space-time?

It is through Equivalence principle. It says that acceleration is indistinguishable from gravity or an attractive force.

Ok. Before you keep asking questions,would you care to show through equivalence principle how gravity can be repulsive or how acceleration can make two bodies appear to repel?

 

[ash64449]

The key concept in that regard is "geodesic deviation" :

http://en.wikipedia.org/wiki/Geodesic_deviation_equation

You will find that for two isolated bodies in space-time, their geodesics converge, i.e. the geodesic deviation is always negative. What that means is that these bodies will approach each other over time. This can be shown mathematically using the geodesic deviation equation; it is simply a consequence of the geometry of space-time.

Don't you think this is same as that of equivalence principle?

I mean didn't he found that gravity is curvature of space-time through equivalence principle and then picking out matrices and getting all other conclusions from it?

 

[Markus Hanke]

Don't you think this is same as that of equivalence principle?
I mean didn't he found that gravity is curvature of space-time through equivalence principle and then picking out matrices and getting all other conclusions from it?

Yes, technically this is the same as the equivalence principle. You can think of geodesic deviation as a way to quantify what the equivalence principle states.

 

[ash64449]

Yes, technically this is the same as the equivalence principle. You can think of geodesic deviation as a way to quantify what the equivalence principle states.

And don't you think acceleration is same as an attractive force(gravity) and cannot be shown as a repulsion? i mean we can only show through experiment conducted by Einstein as an attractive force and never repulsive force?(the same experiment with which he found out relationship between acceleration and gravitational field)