A paradox is a logically self-contradictory statement or a statement that runs contrary to one's expectation. It is a statement that, despite apparently valid reasoning from true premises, leads to a seemingly self-contradictory or a logically unacceptable conclusion. A paradox usually involves contradictory-yet-interrelated elements that exist simultaneously and persist over time.In logic, many paradoxes exist which are known to be invalid arguments, but which are nevertheless valuable in promoting critical thinking, while other paradoxes have revealed errors in definitions which were assumed to be rigorous, and have caused axioms of mathematics and logic to be re-examined. One example is Russell's paradox, which questions whether a "list of all lists that do not contain themselves" would include itself, and showed that attempts to found set theory on the identification of sets with properties or predicates were flawed. Others, such as Curry's paradox, cannot be easily resolved by making foundational changes in a logical system.Examples outside logic include the ship of Theseus from philosophy, a paradox which questions whether a ship repaired over time by replacing each and all of its wooden parts, one at a time, would remain the same ship. Paradoxes can also take the form of images or other media. For example, M.C. Escher featured perspective-based paradoxes in many of his drawings, with walls that are regarded as floors from other points of view, and staircases that appear to climb endlessly.In common usage, the word "paradox" often refers to statements that are ironic or unexpected, such as "the paradox that standing is more tiring than walking".
Hi All;
I was trying to understand Lorentz Transformation equation and special theory of relativity, but as I compared the derivation with a thought experiment I created I found the whole Lorentz Transformation Equation fails. The details of the problem is given in the pdf file attached. I know...
So here it goes:
2 points in space A & B.
1 superluminal object (fixed at 10c, no acceleration) that periodically transmits photons as soon as it starts moving.
1 observer with a very high accuracy photon counter removed a sufficiently large distance from the 2 points for light to take a small...
Shankar ("Principles of Quantum Mechanics", 2nd ed.) shows that the free particle propagator "matrix element" is given by (see p. 153):
## \qquad \langle x | U(t) | x' \rangle = U(x,t;x') = \left(\frac{m}{2\pi\hbar it}\right)^{1/2} e^{im(x-x')^2/2m\hbar} ##,
which can be used to evaluate the...
Here is a scenario in which two twins age at different rates even though both always have the same speed.Consider a train track that includes a circular segment with ground circumference minutely greater than 80. Two twins are on a train with synchronized watches (Frank at the front and Reba at...
NOTE: This is NOT a homework problem. I created this one myself based on some problems I have seen, with specific numbers used to make calculation clean and easy.
Tl/dr version: in a round trip to a star, will the "moving clock" run slower on the way there but faster on the way back due to the...
Hey Friends,
In Einstein's special relativity I find "Twin Paradox", where Dick and Jack, two twins . one of them went to space at a speed of 0.80c to a star 20 light year away (where c is the speed of light) and other remains on earth. When Jane returned to Earth his age was...
Hi ! So a friend and I were solving some mechanics problems in class today. And we came across a pretty funny mathematical paradox. So basically we tackled the problem in different ways...but we ended up with different equations...and none of us could prove the other wrong !
So here goes...
The...
Which way does friction in a viscous disc operate?
Imagine a ring consisting of ringlets. First consider a case of a pair of nearby ringlets - in the same plane, both circular orbits.
If all particles of both ringlets are in circular orbits in the same plane, then they can never collide and...
Assume A and B are at rest on Earth initially. Then B travel to to one light year far away from Earth with an extremely low speed (even slower than a car). So I can assume their ages are the same after B has arrived, right? Then, B returns to Earth with an extremely fast speed (~0.9c) and A and...
Can you please explain what the core problem of the information paradox is?
Hi all!
I've read many articles about it, watched videos, argued with some physicists, and yet I can't grasp at all where the paradox lies.
For example, from the Wikipedia:
"An important difference between the black...
A number can be random even if limitations are applied to the outcome - e.g. selecting a random integer between 1 and 5 restricts the outcome to one of 5 numbers, but the outcome is still random. The same would be true of between 1 and 2; although there are heavy restrictions, an unbiased...
Admit it. It's a pretty dang hard question, but here it is compressed down.
So theoretically it's impossible to have either one, but never mind that. A immovable object has to be an object that cannot have its own speed or velocity changed, so it is an object that cannot be accelerated, since...
I was hoping I could get some help on wrapping my head around the twin paradox. The problem is I have never seen the following "contradiction" addressed. I understand (at least on paper) that events simultaneous in one frame needn't be simultaneous in another. But consider the following...
A fluid with forced vortex flow and constant angular velocity is given. Newton's shearing says there must be strain due to differential linear velocity. The problem is, the difference of linear velocity is only visible to the external observer, the fluid particles themselves do not observe...
I am pretty familiar with the theories of special and general relativity. I know how to add velocities, I know the main postulates and the experimental confirmation. However, I thought of the following thought experiment:
There are 3 experimenters (at the same point in space), who adjust their...
Hi everyone,
I just wanted to know/understand that, why do the dielectrics don't get polarized, when subjected to induced electric field ?
Because, according to the definition of electric field(which is a vector), it is the force per unit charge, which implies, that electric field has a unique...
There's something very curious about Faraday's Law that results from considering a closed curve in space (and any surface whose boundary is that curve). Forget about conducting wires and EMFs: Faraday's Law gives the result of the integral of E along the curve in terms of the rate of change of...
Hello, I just thought of something that looks like a paradox to me. Suppose you have a device which can detect a light source's frequency, and will explode if the frequency exceeds a threshold value f_t. Place this device stationary wrt the light source. Now, suppose there are two observers, one...
If you seal a loudspeaker at the end of a tube and close the other end of the tube you will get standing waves; but what are the boundary conditions at the speaker for the sound pressure wave?
Pressure =0 or Pressure = MAX? I find no mention of this in the literature.
To find out I performed a...
Galaxies outside the observable universe are moving away from the Earth faster than the speed of light. As the two bodies move apart, the gravitational force between them should weaken however as the speed of gravity is equal to the speed of light, the gravitational force would not do so. It is...
Bee Hossenfelder was live-blogging from Stockholm Conference on BH info puzzle today Tuesday 25 August.
Herewith:
http://backreaction.blogspot.com/2015/08/hawking-proposes-new-idea-for-how.html
The conference is 24-29 August. Hawking presented his idea Tuesday, based on joint work with Malcolm...
Imagine an infinitely long wire carrying current i1 in west to east direction. At a small distance 'd' above the wire there is another small current carrying wire of length 'l' carrying current i2 from east to west direction (opposite to the direction of current in the below placed wire)...
[Mentor's note: This thread is forked from https://www.physicsforums.com/threads/bell-spaceship-paradox-quantitatively.828670/ for discussion of the basic principles behind the spaceship paradox]
Suppose the string was replaced by some structure which linked the ships together to make a longer...
Yesterday, I found the time to write a bit further on my SRT FAQ and wanted to give a quantitative analysis of the Bell space-ship paradox on the example of the two rockets accelerating with constant proper acceleration, and I found a problem, I cannot solve. So I took this section out from my...
Since I am new to the forum here, I apologize in advance that in case similar example has been explained in another thread. If so, please kindly refer me to the appropriate place to read further.
In my example, there will be four reference objects, earth, E, distant star, S, spaceship A, and...
I read somewhere that you cannot tell the difference in position between a photon (Or any other particle) at some point in time and the same photon (Or other particle) less than a Planck time later, because it would not have traveled further than a Planck length, which apparently is the smallest...
Here's my equation y= sqrt (x+4)+1
I want to find the x intercept. Ok so i replace y with 0 and solve for x
0= √(x+4)+1
-1=√(×+4)
(-1)2=×+4
1=×+4
-3=×
So it looks like the x intercept is (-3,0)
But then when i go back and plug in -3 in place of x...
y=√(-3+4)+1
y=1+1
y=2
I now have a point...
Dear PF Forum,
After all these post'. I want to know that my understanding of twins paradox is close enough.
So, Green travels, Blue stays.
Blue keeps sending signal, Green bounces the signal.
Doppler factor = 1/4, so ##\frac{1}{4} = \frac{1-v}{1+v}; v = 0.6##
And at event T0 (from B), Green...
Assume that we have a conductor of any shape, say a ball of copper. At electrostatic equilibrium, it is well known that the potential inside this conductor is constant, for otherwise free charges would move from points of highest potential to points of lowest potential (this includes the surface...
Hey There,
I would like to share something that crossed my mind the other day, a solution to the grandpa paradox.
My solution is quite basic,
The Man in the future is going to shoot himself in the past through a portal, He will not do so because if he did, he wouldn't exist in the future to...
I think that both methods (1 and 2) of Bertrand Paradox may be equivalent if the probability is represented by area of the circle enclosed by each method rather than by distances.
Please see the attached file.
In both methods, the probability is approximately 0.6.
Mods: I am not sure if this is a Physics question or more appropriate for Cosmology.
I read a short discussion (on another forum) about the Boltzmann Brain paradox. I did a little further reading on the web but most explanations were a bit too deep (read: over my head). I wonder if someone...
So I'm just really curious and this question is fictional, I'm new so i don't know if this is the right place to post this. Anyway, if there is 2 portal facing each other vertically and a person jump on to it, end up falling forever, i wonders how much could that person reach and is there anyway...
Homework Statement
In the twin paradox suppose the twins are named Dick and Jane. And they both are 20 years old.Dick takes off on a voyage at a speed of 0.8c to a star 20 light years away.Lets say that both the twins send each other signals once a year while Dick is away.How many signals does...
Zeno said that you can't finish or start a race because there is an infinty of points between any two points.
Let's take a distance of say 1meter. As per zeno there is an infinity of points in this distance.
So, what is the size of each of these points. Of course, 1/infinity=0. i.e. each point...
Dear PF Forum
I want to know about these questions that are still bothering me,
Does the universe have preferred frame of refference?
Why there's twins paradox?
Motion is relative, why 1 clock experiences time dilation while the other doesn't?
V = \sqrt\frac{3}{4} ≈ 86.6\%
If V define ratio of...
if there is an uniform, infinitly extended,magnetic field that is changing with a law B(t), I can calculte the induced electric field using an arbitrary circle; then the induced circuitation on the circle is \epsilon _i=-\pi r^2 \frac{dB(t)}{dt} , and since the symmetry of the system ( infact...
Dear PF Forum,
Can someone make it clear for me?
Perhaps I should ask a very simple question. Concerning just one direction.
The distance between Earth and Star T is 100 lys.
The clock is synchronized for A and B
And as PeterDonis pointed out at my previous thread.
Which I believe 87% is an...
Dear PF Forum,
Sorry if I ask (again) about twin paradox, after so many question about this topic here.
Supposed T is a star 100 ly from earth.
If B travels to T from earth
A. Is the symmetry broken?
B. If B watches A's clock at Earth and A watches B's clock at T, do they see the other clock...
I started a thread previously (https://www.physicsforums.com/threads/time-dilation-happens-on-moving-frame-but-which-one.814622/) around this concept but it got closed by one of the staff after helpfully pointing me to...
The "triplet paradox" that comes up in my Googling and search results involve one triplet that stays at rest and the other two venture out and back again, but in opposite directions. Essentially two "twin paradoxes" occurring together.
But what about a scenario in which triplets A and B are...
I have once again (this time in http://www.economist.com/node/2099851) come across the argument that a fuzzy logic solves the liar paradox by assigning the liar sentence a truth value N, other than T or F, with
[[A]] = N ⇒[[~A]] = N. However, I don't see that this gets around the essential...
Simple question: Can a computer be taught to recognize a paradox?
This assumes the computer has no cognizant reasoning or "self awareness".
It is a plot device used in a lot of science fiction, that the intrepid "flawed" human hero defeats the computer or robot with a simple paradox making it...
i hate to start a new thread.
Is it correct to say there is nothing in the current SM (or SUSY?) that resolves Loschmidt's puzzle of where irreversibility comes from. Or is it (non-commutativity?) a basic feature feature of all QM? If it is a basic feature of all QM, is it thought to require an...
A spaceship leaves earth. One twin stays back, the other is on the ship. The ship accelerates for 5 years with a constant acceleration (the 5 years are in the reference frame of the ship), then it decelerates for 5 years. Then, it turns around and does the same thing again. All the accelerations...
When you see the title of this thread, I'm sure you will either be bored or excited because this is one of those famous 'paradoxes' in SR.
So I read the book by Schutz on the part of explanation behind the twin paradox. There he gave an example of two sisters Diana and Artemis involved in the...
Dear PF Forum,
I have a tought experiment here.
I'm asking about twins paradox, but instead of using twins, I'm using clocks to lock them up in a closed room. Sort of Einstein elevator. (unlike Schrödinger, even in tought experiment, I can't imagine locking human being -- or cat -- in a closed...
Imagine an uncharged solid spherical conductor. Inside this spherical conductor, there is a cavity of a weird shape carved out of it. And somewhere inside this cavity, there is a charge +q.
The charge +q induces an opposite charge -q on the wall of the cavity of the conductor, which distributes...