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# Tag Archives: relativity

## Time dilation and Length contraction

Is time dilation and length contraction hypothetical or is it really an observable fact.

for example,consider a rectangular sheet in a spacecraft moving at some high velocity.

Would an observer in the spacecraft be ever able to see the sheet as a square due to length contraction along its breadth(if the velocity is so so adjusted).

Would a stationary observer in the earth be able to observe the same.

In other words who experiences length contraction?

Also who experiences time dilation?

Asked Ajmal

## Speed of Light – a thought experiment

Suppose that you are a person 1 standing on a planet.You could see a person 2 moving in a space craft.2 has a mirror(on the surface of planet) exactly at is down which is moving exactly with the same speed that space craft is moving(and also,the line of translatory motion of both the craft and mirror are parallel to each other).If 2 has shot a beam of light from the bottom of space ship,as the mirror is moving exactly with the space craft;for 2,the path of light is straight line and gets reflected back along the same path in time t.If you are observing the whole thing from the surface of planet,for you,the path of light would obviously be ‘V’ shaped(let the time taken be t’).As the ‘V’ shaped path is longer than straight path and speed of light is same for observers,the time measured by 2 is obviously not the same as you measure.If you are considered to be reference frame,will the clock of 2 appear to be moving slower than yours? (Asked Charan)

## A Face Book conversation on relativity and its effects

**Relativity** has fascinated many young minds (old too).

http://gty.im/iwdayala0103c

Below is a conversation between a student and a Physics Teacher on Facebook chat.

## Speed of Light

How can the speed of light be a constant, when time is not?

If the rate of time can change depending of speed of matter or extreme gravity, the speed of light is 186,000 miles per second, but a second could flow at different rates.

If light from a star passes close to a black hole where time flows slower, this changes the speed of light we perceive?

Asked Martin

## Entropy

The latest thinking about black holes is that they may not collapse into a singularity at all, but may actually explode back with a “big bounce” once the diameter of the black hole reaches the Planck Scale or maximally compact state and once the “big bounce” diameter expands to that of the event horizon, it would release all of the information that till then had been trapped inside the black hole, back into the universe.

My question is this, if in fact the “big bang” that led to the creation of our current universe was the result of the “big bounce” associated with the collapse of a prior universe, is there any measure of entropy that could detect this. In other words would any measure of entropy differ between the universe caused by “big bounce” n and the universe caused by “big bounce” n+k?

John Egenolf Asked

**The question is left for the visitors to answer**

## Are all theories of Physics based on a mathematics … ?

Are not all theories of physics (general relativity, quantum mechanics and other variations) based on a mathematics of structure? An assumption that the model and its constituents have structure? Structure that assumes space as a necessary, though maybe not formalized component?

Could it be that during a black hole collapse that ALL structure is lost? All space is eliminated. There is no space, only mass/energy?

Posted by Richard

## IF A TRAIN TRAVELS WITH SPEED OF LIGHT; WHAT HAPPENS TO ITS LENGTH??

IF A TRAIN TRAVELS WITH SPEED OF LIGHT; WHAT HAPPENS TO ITS LENGTH?

Asked MARIAN

Answer

According to the theory of relativity, the length will decrease to zero.

Please refer to ther following links for more information on the question.

- http://en.wikipedia.org/wiki/Length_contraction
- http://io9.com/5527521/what-happens-if-youre-traveling-at-the-speed-of-light-and-turn-on-your-headlights
- http://wiki.answers.com/Q/What_happens_when_you_travel_at_the_speed_of_light
- http://www.physics.org/interact/time-twins/special-relativity.html
- http://www.physlink.com/education/askexperts/ae169.cfm