Since the age of the universe is 13.7 billion years, can we say that 13.7 billion years ago was the absolute beginning?
I remember Stephen Hawking said in his book that the Big Bang created space and time, time did not exist before the Big Bang or it is not allowed to ask what existed before...
A physical cup, made of ceramic for example, on a table, is real. But the same cup appearing in your dream is not, because it does not exist in the physical world. It is only an image of the real cup that exists in the physical world. It is created by your brain, but seems real because of how...
Is entropy real? It seems like it's not real because it depends on how you group microstates together into a macrostate, and the way you group them can be arbitrary. For example (at 13:04 of the video below), there are 91,520 microstates in the macrostate “9 in left; 1 in right” but 627,264...
Let's consider the Q in footnote 22 (see image).
Q=##\frac{1}{2}##mω2x2, where ω is a function of t.
Then is ∂Q/∂t = mω##\frac{dω}{dt}##x2?
Even though for simple harmonic motion, x is also a function of t (ie. x=x0##\sin##(ωt), where x0 is the amplitude), we do not care how x depends on t when...
∂Q/∂t refers to the partial derivative, not the total derivative. The book goes on to talk about operators that explicitly depend on time (see attached images).
In doing the partial derivative ∂Q/∂t, we do not care about how x depends on t, but only how Q explicitly depends on t.
But no matter...
Suppose Q=2x+t and x=t2, then ∂Q/∂t=1.
But Q can also be written as Q=x+t2+t, then ∂Q/∂t=2t+1.
We now have 2 different answers. But I think there can only be one correct answer.
In reference to the equation in the image, no matter we write Q=2x+t or Q=x+t2+t, <Q> should be the same, so the LHS...
Yes I meant the response
"There is currently neither conclusive evidence for the multi-histories interpretation nor for the single-history interpretation. We simply do not know which is true at this point in time."
is an impartial, fair response in relation to EPR's response
"What evidence is...
Similarly, someone could say:
"Currently, what conclusive evidence is there of a one-and-only history in the macro world?
There is none.
It's not an opinion. It's a scientific fact."
So an impartial, fair response would be:
"There is currently neither conclusive evidence for the multi-histories...
I realize it's not easy to get neutral, impartial responses. Most of us have our own perspectives, beliefs and biases, and we allow these biases to influence our response, knowingly or unknowingly.
My attempt of an impartial, fair response would be:
"Feynman's sum over histories is a...
Feynman's method shows that the historical path of a particle is not encrypted into the present state of the particle, so this is also true for a collection of particles, this implies that our history is also not encrypted into our present state?
This, at best, says Feynman's sum over histories is consistent with the orthodox, one-history Copenhagen-style interpretation? But Feynman's sum over histories could also be consistent with a multi-histories interpretation?
Before Feynman's sum over histories, most of us were oblivious to or...
What does Feynman's sum over histories mean to the interpretation of our world? Does it mean that we (or a particle) do not have a definite history, but only the most probable one?
Does the sign always say "the cat is alive", even if the cat is found dead when the box is opened? And why must the sign be inside the box? It seems the sign just has a certain probability of being true, say 60% true and 40% false. But is that the same as being in a superposition of being true...
So a photon on the Earth surface experiences an acceleration of 9.81 ##ms^{-2}## too? So its radius of curvature ##r=\frac{c^2}{9.81}\approx10^{16}## m?
But what if it travels straight down towards the Earth? It cannot move faster than ##c##, so its acceleration would have to be zero.
So given...