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Questions related from Derek Abbott
When analyzing a moving body with respect to a moving observer we can use the Galilean or Lorentz transformations. As we approach the speed of light we know the Lorentz transformation gives the...
11 November 2017 6,695 10 View
It is a well-known 'principle' in physics that only the two-way speed of light can be measured. Any experiment you try to construct to measure the speed of light only in one direction results in...
09 September 2015 1,836 5 View
We know that a decelerated charge emits photons. So you can visualize an observer in a stationary frame of reference that detects these photons. However for another observer in an accelerated...
11 November 2014 1,698 26 View
Imagine a pendulum swinging back and forth. When it is at its lowest point the PE = 0 and KE is maximal. Now imagine an observer moving along in the direction of the pendulum, with matched...
11 November 2014 602 1 View
How many uncertainty relationships are there between physical variables? For example the well-known ones are: [momentum,position], [energy,time], [particle number, phase], [angular momentum,...
07 July 2014 2,052 8 View
Are there any multicellular life forms that don't get cancer or where cancer is very rare?What can we learn from these cases?
07 July 2014 977 10 View
We all know the resolution depends on wavelength. However, when a student sees this concept for the first time it does seem paradoxical. After all, the direction in which the wavelength is...
06 June 2014 6,341 4 View
For TEM modes, H_z = 0 and E_z = 0, so we can easily find from Maxwell's equations that TEM modes in, say, coax have no low-frequency cut-off. The TEM modes are dispersionless and exist from the...
06 June 2014 8,552 3 View
Consider x^y, when x = 0, as y --> 0, z --> 0. But when y = 0, as x --> 0, z --> 1. Surely z can't be 0 and 1 all at the same time? What is the resolution to this apparent paradox?
05 May 2014 5,900 49 View
a) See here: https://www.youtube.com/watch?v=BE827gwnnk4 b) It takes 300 Hz to break a wine glass c) Speed of sound in air = 340 m/s d) Wavelength = 340/300 = 1.13 metres e) Speed of sound in...
05 May 2014 6,129 10 View
In a recent paper it has been stated: "It is true that TEM wave modes in a [coax] waveguide do not have a low-frequency cut-off versus the diameter of the [coax] waveguide, but this argument is...
05 May 2014 4,360 46 View
Can you help me understand the chemistry of chlorinated swimming pools? When the pH is tested and found off balance, usually an alkaline power is first added and then some acid a few hours...
02 February 2014 5,042 4 View
The principle of linear superposition holds for the integers, eg. 3 + 4 = 7. However, when we take the integers out to infinity we now obtain nonlinear behaviour. Infinity plus any amount is...
01 January 2014 1,032 42 View
In physics, we have a number of "fundamental" variables: force, mass, velocity, acceleration, time, position, electric field, spin, charge, etc How do we know that we have in fact got the most...
01 January 2014 3,170 6 View
If you look through a standard net curtain that hangs over a window, in your home, and observe the lights in your room there is no special effect. They appear as normal. Now try this experiment:...
12 December 2013 3,195 5 View
a) Imagine you have a microchip with clock speed at 5 MHz. (For example, this was a typical CPU clock speed way back in the 1980s). b) Divide 5 MHz into c = 3 x 10^8 and you get 60 metres. c)...
12 December 2013 3,044 22 View
We want to write our own search engine to find specific regular expressions of interest on the web. However, we don't want to really have to trawl the whole web, as that would take many years on...
12 December 2013 6,595 3 View
Imagine a block of wood resting on two supports at each end. You point a gun upward under the block and shoot the block upwards. One scenario is you shoot the block upwards in the exact center....
11 November 2013 9,178 10 View
It is well known that a yacht can sail against the wind. The method used is called tacking. This couterintuitively means that it is always better to have a wind in the opposite direction...
11 November 2013 7,519 3 View
Other than in a cryogenic lab, is it possible to find a temperature somewhere in the universe significantly lower than 2.72 K, due to the cosmic background, over a sustained length of time? Like...
11 November 2013 7,482 32 View
A mental picture to understand this question is as follows. Imagine an alien spacecraft is on a collision course to crash into Earth and destroy us all. All the aliens in the craft are dead...
11 November 2013 6,879 19 View
At a time dt just before sunset, does your shadow elongate at an infinite velocity?
11 November 2013 5,325 12 View
Ideal pure classical randomness is deterministic and only appears random as a result of complexity and our ignorance of the system. Whereas a quantum event (eg, flip of a qubit or radioactive...
11 November 2013 1,597 15 View
Imagine you have a computer that is a box where you input billiard balls as your input. The box is a computer that arranges to make the balls dynamically interact so that when they exit the box...
11 November 2013 3,370 9 View
If I draw a square on a Cartesian plane and give you an exact copy, imagine we both specify a point inside each of our squares. What is the probability that we have selected the same...
10 October 2013 8,695 40 View
First part of the question is: what are the absolute essential ingredients behind computation? You need (i) switches, (ii) interconnects, (iii) input energy source, (iv) memory, (v) feedback,...
10 October 2013 2,522 16 View
If the universe appeared out of the vacuum due to vacuum fluctuations, is not entropy reduced? And if entropy is reduced, does this not require an external source of energy?
10 October 2013 3,028 18 View
We model the physical world, by looking for invariances and laws, then building mathematical models on top of those. Often we have found that models can be superseded and our picture of the...
08 August 2013 9,695 94 View
It is well known that babies cry just before sleep. Sometimes the cries have specific origins that cause pain or discomfort. But as everyone knows, even when all those factors have been...
08 August 2013 2,126 28 View
Could transcranial magnetic stimulation (TMS) be used to create a new definition if someone is dead or not? And could it play a role in resuscitation (eg. used in conjunction with CPR for a victim...
08 August 2013 5,403 9 View
An iPhone not only has a camera, but can measure orientation, and it also contains an accelerometer. Is there a clever way to exploit an iPhone to perform a weight measurement? How to do it in...
08 August 2013 9,291 2 View
One can obtain a rough upper limit for the maximum number of bits of information the universe could possibly hold as being somewhere around 10^122 to 10^124 depending on which parameters you feed...
08 August 2013 2,121 5 View
If I lift a particle up by a height h, it increases in potential energy by mgh. But the mgh is simply a fictional book keeping device. What is really happening is I slightly increased the...
08 August 2013 8,919 23 View
It is possible to explain the movement of matter purely from the curvature of space-time, thus making the concepts of gravitational field and gravitational force fictitious?
08 August 2013 2,402 17 View
As a possibly pathway to understanding the role the immune system plays in attempt to control cancer growth, an interesting test would be to perform an epidemiological study of those with...
08 August 2013 9,576 21 View
Let us perform an imaginary thought experiment where we have an instrument that can magically convert a particle of mass, m, without moving it, totally into energy via E=mc^2. If we perform this...
07 July 2013 8,518 31 View
The Buffon's needle experiment is one that you can repeat many times, and in the limit it will give you an increasingly accurate estimate of pi the more you repeat the experiment. Simply stated:...
07 July 2013 2,330 8 View
If we look at the formula for the inverse square law for force between two charges Q1 and Q2, a permittivity term is in the denominator. If the permittivity was hypothetically zero, the force...
06 June 2013 2,116 10 View
If we look at the analogy of electrons and holes in semiconductor physics, we see that holes appear real in many ways: we can physically measure their apparent mass and all sorts of electrical...
06 June 2013 2,577 16 View
Alice & Bob enter a game where each have a necktie and they call an independent judge to decide who has the better looking necktie. The judge takes the better necktie and awards it to the other...
06 June 2013 6,189 27 View
We know that the noise from a resistor in thermal equilibrium cannot heat up another resistor, even if you connect them via an electrical isolator. This is the Second Law of thermodynamics. But...
06 June 2013 5,200 6 View
Here is the problem: 1. Alice wants to phone Bob. 2. Alice dials Bob's number and the person at the other end claims to be Bob's son Charles. 3. Bob and Charles have indistinguishable voices,...
06 June 2013 6,489 18 View
More journals these days are requiring an ethics statement if a human was involved in an experiment. But are there some trivial no-risk classes of experiment for which no approval is universally...
05 May 2013 7,455 41 View
When integrating using the method of residues, one needs to check if the integrand satisfies the Cauchy-Riemann equations first. However, it is possible to have an integral that doesn't satisfy...
05 May 2013 747 11 View
Are there limits to the size of the double-slit experiment? Can we in principle emit single photons with lower and lower values of hf and consequently increase the spacing between the...
05 May 2013 3,402 10 View
Can a single photon source be set up in a way that we know the time when each photon is emitted? It seems to me that it ought to be impossible to determine the time. If it were possible, then in...
05 May 2013 4,470 9 View
A corollary of Kirchhoff's law of thermal radiation is that if bodies are in thermal equilibrium with each other and the cavity they are in, you will not be able "see" them with a passive...
05 May 2013 2,945 16 View
If you photocopy a black sheet of paper, it comes out black. If you photocopy a white sheet of paper, it comes out white. But, interestingly, if you put a mirror face down on a photocopier is...
05 May 2013 1,818 7 View
We know that variables such as spin, polarisation, position, particle number, energy, etc can exist in a quantum superposition. Variables such as charge, pressure, temperature, entropy etc do...
05 May 2013 3,753 20 View
a) My microwave oven operates at 2.45 GHz and has a mesh screen behind its window. b) My smartphone receives both WiFi connections as well as standard cellular calls. c) I put my phone in the...
05 May 2013 6,772 2 View
It's generally thought that mtDNA is only maternally transmitted. But is there any evidence at all for paternal mtDNA transmission? What about during ICSI? And if so, what are the implications?...
12 December 2012 2,988 3 View
It is well-known that in quantum mechanics, [position, momentum], [angle, angular momentum], [energy, time], and [phase, particle number] are all conjugate pairs and have an uncertainty relation....
12 December 2012 5,306 77 View
If a billiard ball hits a stationary billiard ball, it comes to rest. Then the original stationary billiard ball begins to move off. Kinetic energy is said to transfer from one ball to the other....
12 December 2012 9,674 4 View
It is interesting how maths is useful for describing the physical world. But are there any branches of mathematics that are totally useless for physics? Why? Could it be that we perhaps...
12 December 2012 7,871 93 View
A monochromatic beam of, say, red light appears red to the human eye. However, if we chop the beam with a mechanical shutter, we get a square wave. Fourier's theorem predicts that this beam will...
12 December 2012 6,560 1 View
It is easy to design a circuit, using operational amplifiers, for example, which produce either negative resistance, negative capacitance, or negative inductance. This is often taught in...
12 December 2012 2,477 35 View
Planck's black-body equation has an 8*pi in front of it. When deriving the equation, it starts off as a 4*N*pi, where N=2 and the usual argument for setting N=2 is to account for two orthogonal...
11 November 2012 6,792 19 View
It is known that the velocity of an unpowered yacht can be faster than the velocity of the wind driving the sails. Can anyone explain this phenomenon? I'm looking for the clearest and simplest...
11 November 2012 6,518 11 View
When you block polarized light with a crossed polarizer, the polarizing filter absorbs photons and the filter gets hotter as a result. Thus the energy gets converted to heat. However, what...
11 November 2012 3,329 35 View
It was always thought impossible to have a closed-form formula that can calculate an arbitrary Nth digit of pi, until Borwein produced a formula in base 16 in the mid-1990s. My question is why...
11 November 2012 7,603 32 View
Einstein's principle of equivalence says that you can't tell the difference between being in a stationary elevator in a gravitational field and an accelerating elevator in free space. However, if...
11 November 2012 3,597 14 View
