Special Relativity & Twins Paradox - Is it real?

[wjz]

I read Einstein’s twins paradox (http://www.einstein-online.info/spotlights/Twins) and I found it very hard to believe.

 

How can the traveling twin returns to find his brother older when he comes back to earth? If the aging is calculated by heart beats then both of them had the same count of heart beats during this trip.

 

What will happen when someone is traveling with a speed as near as speed of light? Let’s think about the following scenario to understand more. If you are driving your car and look in the mirror on a car that has the same speed, then it will look like as if the car is not moving. If the speed of the other car is higher, then it will be moving toward you. If it is slower it will be moving backward. The same effect would happen when traveling with a speed that is close to speed of light.

 

Let’s assume that the first twin is driving his car on earth, and the second twin is leaving earth with a speed near speed of light (accelerating from 0 to 95% of the speed of light), at slow speed he will see the car of his bother moving regularly and as he increases his speed his brother will start to appear slowing down. When the velocity reaches exactly the speed of light he will see the car not moving (because he is moving with the light coming from the car when it was in a specific point). When the speed exceeds the speed of light he will start to see the car moving backward (traveling to history).

 

The paradox is misleading because it does not consider what will happen when the brother is on his road back, in that case the contrary effect will happen, the car that was moving backward will slowdown, and stop and move forward again, and when the brother reaches earth slowing down to speed near 0, he will see his brother moving with expected speed and reaching the expected point.

 

Today we can see stars that do not exist currently anymore, because it took the light long time to reach earth, same would happen if we can travel to another universe with speed that exceeds the speed of light (using black holes or any other mean), the same effect will happen, we will be seeing the history of earth (because the light coming from the history of earth has just arrived to the other far universe!). So if we can take with us a very complex technology that enables us to see extremely far places like earth from the other universe, then we will be able to see dinosaurs. When we come back to earth with the same speed the effect will be rolled back and we will come back to current moment.

 

So I think the whole thing is illusion, related to light, and related to whether we can reach a point before the light can reach it or not, when coming back to earth that illusion will go away, and we come back to reality!

 

[ACG52]

That's totally wrong, in all respects.

[swansont]

GPS satellites must have their clocks set to run at a different rate than clocks on the ground so that when they are in orbit under the effects of relativity they will work properly. Their "heart beat" rate changes. It's a real effect.

[Janus]

You are confusing Doppler effect for time dilation. Time dilation is a slowing of the moving clock that is "left over" after you account for the delay caused by the traveling of light between objects.

 

IOW, the traveling twin's heart actually does beat fewer times than his stay at home brother.

 

If The observed Doppler shift was just due to the finite speed of light, then yes, things would work out as you say. You would see someone's clock slow down as they moved away and speed up as they approach with the two effects canceling out and having both sets of clocks reading the same when they meet back up.

 

However, the Doppler shift we actually measure is not what you would predict from just the increasing delay due to increasing distance.

 

It works out to be

 

[math]\sqrt{\frac{1+\Beta}{1-\Beta}}[/math]

 

where Beta= v/c and is positive if the velocity is towards the observer.

 

So let's consider a simple example:

 

A clock which is identical to your own heads away from you at 0.5c, travels 1 light hr and then returns at the same speed.

 

Here is what you will see:

 

As the clock moves away you see it tick at a rate of 0.577 that of you own clock. After 2 hrs by your clock, the other clock reaches the point where it turns around. However, since this is 1 light hr from you, you will not see this for another hr. This means that for 3 hrs you see the other clock tick at 0.577 that of your own and tick off 1.732 hrs. You then start to see the clock start to come towards you and tick at a rate of 1.732 that of your own. it does this for the hr it takes for the clock to reach you. (the total round trip takes 4 hrs by your clock.) so the other clock ticks off another 1.732 hrs for a total of 3.464 hrs. the other clock will have ticked off only 3.464 hrs for the 4 hrs your clock ticked off.

 

The other thing to be aware off is that actual real life experiments bear out this result. We have sent very accurate clocks in planes around the Earth and noted the difference in their times when they returned. We measure short-lived particles that are formed high in the atmosphere striking the surface of the Earth even though they shouldn't have lived that long. (the only reason they do is because, due to their high speed, they age much much slower than normal). Every the theory is confirmed in particle accelerators around the world.

 

The point is, before you go around claiming that an accepted theory is wrong, you really need to get a good understanding as to why it is accepted. Scientific theories are not adopted easily. They go through a trial of fire where everyone tries to pick them apart and find the flaws. If your argument had any basis at all, Relativity would have never reached the level of acceptance that it has. It would have been shot down immediately.

[pzkpfw]

... So I think the whole thing is illusion, related to light, and related to whether we can reach a point before the light can reach it or not, when coming back to earth that illusion will go away, and we come back to reality!

 

 

It's not "just" an illusion, it's been experimentally verified. e.g http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

 

What I'm about to write is "wrong", but it's the way I think about this stuff, to help me comprehend it. Again - it's "wrong"; just an analogy. (See above for better technical explanations).

 

Basically: the twin who leaves and comes back has, by changing frames (by accelerating), travelled further in space. Because they travelled further in space, they travelled less in time.

[swansont]

 

It's not "just" an illusion, it's been experimentally verified. e.g http://en.wikipedia.org/wiki/Hafele%E2%80%93Keating_experiment

 

What I'm about to write is "wrong", but it's the way I think about this stuff, to help me comprehend it. Again - it's "wrong"; just an analogy. (See above for better technical explanations).

 

Basically: the twin who leaves and comes back has, by changing frames (by accelerating), travelled further in space. Because they travelled further in space, they travelled less in time.

 

Not a good analogy. Their length contracted. They traveled less in space, so it took less time.

 

The spacetime interval has a subtraction — it's not the familiar Pythagorean relationship for length of a resultant vector, so the conservation you imply doesn't exist.