time dilation

[general1]

I have heard that when astronauts travel to outer space they travel forward in time into the future and are a few seconds younger when they return to earth. Is this true or are they just ageing slower due to the difference in their velocity to ours. What is actually physically happening to the atoms in their bodies?

[ACG52]

The difference is not due to relative velocity so much as it is their position in the gravitational field. Their time is relatively faster, due to the lower gravitational field. What physically happens to the atoms is the same as what happens on earth, just at a different relative rate.

[general1]

Thank you for the answer.it seems to me then that their is no such thing as time. The past has already happened and the future hasn't happened yet. Their is only now. Their is only motion of matter in space and that motion is different all over the universe depending on the gravitational field that the matter is in.am I on the right track?

[ACG52]

Pretty much. It also depends on relative motion. All time is relative. But then, all space is relative too.

 

As to what is time, I like John Wheeler's definition.

 

"Time is what keeps everything from happening at once".

Edited May 19, 2013 by ACG52

[general1]

I got really interested in this subject when I read about how we derived at one of the smallest units of time that we all use (the second).the atomic clock uses a laser beam to vibrate an atom 9 billion times. This is a second. If you put the same atomic clock near the center of the galaxy, one second would take like 10 thousand years on earths frame of reference pretty cool stuff.

[ACG52]

Your numbers are way off, but the principle is there.

[swansont]

The difference is not due to relative velocity so much as it is their position in the gravitational field. Their time is relatively faster, due to the lower gravitational field. What physically happens to the atoms is the same as what happens on earth, just at a different relative rate.

 

That depends on their altitude. Below a few thousand km, the frequency shift is negative, as the kinematic term is larger than the gravitational term. Thus, astronauts who have been on the shuttle or the ISS had their time slow down.

[krash661]

Pretty much. It also depends on relative motion. All time is relative. But then, all space is relative too.

 

As to what is time, I like John Wheeler's definition.

 

"Time is what keeps everything from happening at once".

and

space is what keeps everything from happening to me.

 

nice touch alex.

[DimaMazin]

Pretty much. It also depends on relative motion. All time is relative. But then, all space is relative too.

 

As to what is time, I like John Wheeler's definition.

 

"Time is what keeps everything from happening at once".

Time isn't relative because addition of times is simple without Lorentz's transformation .Time is scalar.Experiments prove it.All observers can always agree whose time is slower and whose time is faster.

Edited June 1, 2013 by DimaMazin

[swansont]

Time isn't relative because addition of times is simple without Lorentz's transformation .Time is scalar.Experiments prove it.All observers can always agree whose time is slower and whose time is faster.

 

 

No, this is false. In inertial frames one cannot have this agreement. Only by having a change of frames can one identify whose time is slower and whose time is faster.

 

Time isn't relative because addition of times is simple without Lorentz's transformation .Time is scalar.Experiments prove it.All observers can always agree whose time is slower and whose time is faster.

 

No, this is false. In inertial frames one cannot have this agreement. Only by having a change of frames can one identify whose time is slower and whose time is faster.

[DimaMazin]

No, this is false. In inertial frames one cannot have this agreement. Only by having a change of frames can one identify whose time is slower and whose time is faster.

 

 

No, this is false. In inertial frames one cannot have this agreement. Only by having a change of frames can one identify whose time is slower and whose time is faster.

Then in frame of muon,which is fast traveler relatively of Earth,motionless (relatively of Earth) muon decays later. Of course you can prove it never.Because traveling(relatively of Earth) muon can collide with particles of decay of motionless(relatively of Earth) muon.

[ACG52]

. Of course you can prove it never

Nonsense. Do you ever try to look anything up before posting on it?

 

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

[DimaMazin]

Nonsense. Do you ever try to look anything up before posting on it?

 

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

Contracted distance and slowed time of motionless(relatively of Earth)muon,in frame of fast(relatively of Earth)muon,can't cause decay of motionless(relatively of Earth) muon earlier than collision of the muons will happen.However the decay happens earlier than the collision.

Edited June 2, 2013 by DimaMazin

[swansont]

Then in frame of muon,which is fast traveler relatively of Earth,motionless (relatively of Earth) muon decays later. Of course you can prove it never.Because traveling(relatively of Earth) muon can collide with particles of decay of motionless(relatively of Earth) muon.

 

Are you saying the reduction in muon flux is due to collisions rather than decay?

 

If so, prove it. Find the muon cross section for interaction and show that passing through the atmosphere you should expect those losses.

[DimaMazin]

Are you saying the reduction in muon flux is due to collisions rather than decay?

No.

[swansont]

No.

 

Then what collision are you referring to?

[DimaMazin]

Then what collision are you referring to?

Motionless(relatively of Earth) muon is created at basis of Earth( at the same time the moving muon is created). The motionless muon decays earlier than their collision can happen.Therefore in Earth's frame they can't collide.What causes the decay of the muon earlier than their collision happens in the moving muon frame?In fact the distance is contracted.

[Janus]

Motionless(relatively of Earth) muon is created at basis of Earth( at the same time the moving muon is created). The motionless muon decays earlier than their collision can happen.Therefore in Earth's frame they can't collide.What causes the decay of the muon earlier than their collision happens in the moving muon frame?In fact the distance is contracted.

 

Here's what I assume you mean:

 

A muon which is at rest with respect to the Earth is formed at the surface of the Earth at the same time as a fast moving (with respect to the Earth) is formed in the Upper atmosphere.

 

According to the Earth frame, the first Muon decays before the second muon can reach it. However, if time dilation is reciprocal, then according the frame of the second muon, it should reach the surface of the Earth before the first muon decays. Thus if the first muon is in the path of the second, they should collide in according to one frame but not the other.

 

The problem here is not the reciprocal nature of time dilation but the phrase "at the same time". "At the same time" does not mean the same in both frames. If the first and second Muon are formed at the same time in the Earth frame, They are not formed at the same time according to the frame of the second muon, according to it, the first muon formed well before the second muon does. So far before that it's expends it longer life time before they can meet.

 

If instead, they form at the same time in the second Muon frame, then according to the Earth frame, the first Muon forms well after the second Muon, and thus lives to meet the second Muon.

 

In either situation both frames agree as to whether or not the Muons meet each other, they just don't agree on the order of the creation of each Muon.

 

This is the Relativity of Simultaneity. Just about any time someone comes up with what they think is a contradiction in Relativity, it is because they neglected this effect.

[DimaMazin]

Here's what I assume you mean:

 

A muon which is at rest with respect to the Earth is formed at the surface of the Earth at the same time as a fast moving (with respect to the Earth) is formed in the Upper atmosphere.

 

According to the Earth frame, the first Muon decays before the second muon can reach it. However, if time dilation is reciprocal, then according the frame of the second muon, it should reach the surface of the Earth before the first muon decays. Thus if the first muon is in the path of the second, they should collide in according to one frame but not the other.

 

The problem here is not the reciprocal nature of time dilation but the phrase "at the same time". "At the same time" does not mean the same in both frames. If the first and second Muon are formed at the same time in the Earth frame, They are not formed at the same time according to the frame of the second muon, according to it, the first muon formed well before the second muon does. So far before that it's expends it longer life time before they can meet.

 

If instead, they form at the same time in the second Muon frame, then according to the Earth frame, the first Muon forms well after the second Muon, and thus lives to meet the second Muon.

 

In either situation both frames agree as to whether or not the Muons meet each other, they just don't agree on the order of the creation of each Muon.

 

This is the Relativity of Simultaneity. Just about any time someone comes up with what they think is a contradiction in Relativity, it is because they neglected this effect.

Yes.Thanks.

[DimaMazin]

Is life time of the first muon longer than life time of the second muon in frame of the second muon?

[xyzt]

 

 

It's worth a visit just for the synopsis alone, and it's free. I know there is a web site as well under the title name. If you have read this book please enter a post and let me know as there are some things that I do not quite understand regarding the E=MC2 section. That bit has me perplexed as I thought that this was nailed but after reading this I am in great doubt about how valid or invalid it is. Hoping to hear from someone soon,

Alan.

I looked at the "book", it is totally crackpot. Self-published by a crank called Syd Wilcox , quoting the "papers" of a (better known) crank, Paul Marmet. You wasted your money.

[md65536]

Is life time of the first muon longer than life time of the second muon in frame of the second muon?

Yes. According to a clock in the second muon's frame, during the short lifetime of the 2nd muon, the first muon ages a small fraction of its lifetime. (And vice versa.)

[DimaMazin]

Yes. According to a clock in the second muon's frame, during the short lifetime of the 2nd muon, the first muon ages a small fraction of its lifetime. (And vice versa.)

Still you don't define simultaneity as xyz without t.