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# Category Archives: Relativity

## 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.

hlo sir,
HELLO

did u watch interstellar movie??
no

kk… i hv a doubt regarding g concept??

## What is the mechanical energy of a bird on top of a moving Ship?

A bird is at rest on d top of a stick of moving ship….!! what is the mechanical energy that exists in the bird ???” – This question was posted by Fatima

Answer: The mechanical energy of the bird is both Potential and Kinetic as the bird is at a height with respect to ground and the bird is in motion along with the ship.

(Any deeper discussion is welcome)

## Negative Mass

“Can mass be a negative? if yes plz explain me…”

Negative mass is a hypothetical concept. In normal case mass is always positive as it is of one kind only.

Some argue that this (+ mass) is in our universe (?) and there is equal probability of having a negative mass somewhere else.

In Casimir Effect ( A quantum phenomena :: Find details at http://en.wikipedia.org/wiki/Casimir_effect) properties similar to the expectations from negative mass were reported. (i.e; then the force between two masses becomes repulsive)

The concept of negative mass and the consequences thereof are widely discussed in the theory of wormhole and related ideas.

The existence of negative mass will violate more than one conservation principles in its present form.

## Mass of a charged particle !

“Can mass of a charged particle be infinite and if
yes explain how and when?????”

Answer: Please note that charge is independent of speed but mass depends on speed. So of a body of any mass is moving with gradually increasing speeds, its mass goes on increasing as per the theory of relativity (The relativistic mass $m=\frac{m_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$) but the charge remains the same.

Therefore, the mass of a charged particle can be infinity.

(If any of the visitors has got a different opinion, please post them as comments to this post.)

## Determinism, quantum theory and …. ?

It is known that the behaviour of microscopic particles and systems cannot be predicted.Like, the exact position of an electron cannot be determined ,but that we can give only a probable region where this can be found.So can this theory be applied to support (at least theoretically)the existence of parallel universes,where the lack of determinism in Quantum Theory can be applied ? Suppose in one universe something happens,the reverse happens in a parallel universe,just like the position of electron is indeterminate?

Can the theory of existence of parallel universes be refuted or proved?

Ans:

Such a question I have discussed elsewhere in the site already. The theory of parallel universes or multiple universes is one which comes into discussion when quantum mechanics and the theory of probability is discussed.

Schrödinger’s cat is a relevant thought experiment which can be considered in this discussion.

Imagine a cat inside a box. The box is provided with a mechanism which triggers a system which inject potassium cyanide to the cat. The box is also provided with a single atom of a radio active substance. The life period of a single atom of a radio active element varies from 0 to infinity. SO, the atom may or may or decay in a given time interval. If the atom decays, the radiation emitted will trigger the cyanide injection system and it will instantly kill the cat.

If the cat is inside the box and the box is kept closed for one hour, What is the state of the cat?

When after one hour we open the box and see, we will EITHER  see a DEAD  cat or a LIVE cat depending on whether the atom decayed or not.

But the probability of decaying or not decaying of the atom during the one hour are equal. Then when we are not looking at the cat, what can we say about the state of the cat?

We can say that it is the superposition of the two probabilities. But when we make an observation, only one of the probabilities become a reality.

What happens to the other probabilities?

Some say that there is a MASTER MIND which determines which of the two (or many) probabilities should become the reality. One of the many probability becomes a reality and all others collapse.

It’s right to remember one saying in this context;

“To say YES to somebody is to say NO to all others”

The another theory explaining the probability turning to reality is that, whenever we make an observation, or take a result, the universe splits into as many as the number of probabilities.

So, it’s not a Universe, but a MULTIverse.

We don’t know what actually is taking place. But it’s very thought provoking to read and think on such ideas and theories.

Here are some links which you can use for further reference.

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