Home » Posts tagged 'quantum mechanics' (Page 2)

Tag Archives: quantum mechanics


A Quantum Physics based Question : Can Anyone answer this?

Can anyone answer this Quantum Physics Based question posted by Ian Mc Tavish?

“I would very much like someone who has access to the necessary equipment to perform the following suggested experiment or let me know if this has already been done and what the results were.

I should apologise in advance for my lack of proper scientific terminology as I have had no formal physics training other than the thought experiments I have posed to myself and reading a few books on physics and astronomy and articles online.

Firstly, I understand that when light is shone through two slits it causes a pattern of light and dark on the screen behind thus suggesting that light is a wave.

Secondly,  when the rate at which the light is emitted is slowed down so it can only be a photon(?) at a time there is still an interference pattern.  Suggesting the photon goes through both slits at the same time and somehow interferes with itself….giving birth to quantum physics and a whole lot of outlandish theories (I have an even more “outlandish” theory myself)

Finally, it gets even stranger, when any kind of device is put in place to measure or count which slit each light particle is going through, the pattern changes to diffuse. At last being what you would expect to see from individual particles.

The strange part is, of course is how can just the act of observing cause a diffuse pattern. If the measuring device is switched off it goes back to bands of light and dark.

I hope I have this reasonably correct so far ?

SO…..what would happen if the device that measured which slit photons went through was powered by some kind of voltaic cell that was placed where the light bands are.

That is to say only when the light was making the banded pattern would the power be sufficient to switch on the device measuring which slit the light particles went through….which will then make the pattern diffuse….which will switch off the machine…….which will then make the pattern banded……which will switch on the machine…..ad infinitum.

This seems to cause the same paradox as Schroedinger’s Cat but a lot easier to test and more animal friendly…..a bit of Hawkins style humour there…haha.

If this is the first time someone has suggested this and it does prove useful in any way I would very much like to make my parents proud and have this referred to as the “McTavish Twist”.   The first part being my surname and “twist” because I love twists in both science and cocktails !!!  Both are refreshing and alleviate the boredom..

One suggested result is that the measuring device switches on and off at the speed of its slowest component.  If there was nothing slowing down its rate of switching then it would be very interesting to measure the number of times it changes state per second ?  Although I imagine this may take some clever machinery indeed as the resulting figure should be the smallest possible measure of time.  A “universal tick” ?  (maybe we can call it a “McTavish Tick” or am I getting greedy !!).  I imagine this should link mathematically to the maximum speed of light in some way.

Another possible outcome is that the machine will not switch on even though the light level appears sufficient to power it.  This could happen because it is only really at half power…..being half in the diffuse pattern (that is to say half in another state/universe).  It may be interesting to note where the “tipping point” is ?  Does it really work out to be exactly one half or does it lean more towards one state ?  Again this ratio may link mathematically to another well known number.

I imagine the actual results of the experiment will lead as usual to more questions.  I would very much like confirmation of the results so my own thought experiments move on to new questions too.

Thank you sincerely for your attention.”

Experts in the field are requested to respond

Determinism, quantum theory and …. ?

Anchu Wilson asked:

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?



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?

Is it dead or alive?

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.

Black Holes and Thermal Radiation

Varun G asked

“Do black holes produce thermal radiation, as expected on theoretical grounds and do they absorb light?”

Ans: Hope you are talking about the Hawking radiation.

Any body at a temperature above absolute zero emits radiations. If the temperature of black body is not absolute zero (It was Stephen Hawking who predicted that black holes should have a finite, non-zero temperature, and hence the name “Hawking Radiation”) it will emit radiation.

In a black hole emitting radiation, there is a loss of mass. If the mass decreased due to Hawking Radiation is more than the mass gained by the black holes via alternate means, the net mass of the black holes will go on decreasing. (This is called “black hole evaporation” Further, it has been noted that the black holes with lower mass emit more radiations than the heavier ones.

This answer may seem contradicting the definition of black hole itself.

“A black hole is a body whose gravitational force of attraction is so huge that even electromagnetic radiation cannot escape from it” as the definition goes.

But the Hawking Radiation is caused by Quantum effects. The processes behind the “escape” of radiation from a black hole is thought to be

  • Vacuum Fluctuations and
  • Quantum tunneling

The above terms and concept will be too high to be discussed at school level. However for the curious ones, I am giving some links to explore.

%d bloggers like this: