時光起源, 2

Posted on November 3, 2023 by rpflee

The Origin of Time, 2

In general, on average, a large object moves slower than a small object, because each one’s speed is constrained by its slowest component particle and the large object consists of more particles.

In other words, if the two objects have identical particle components and identical particle densities, the large object has a bigger inertia than the small one.

“Being constrained by other component particles” is the exact cause of the existence of mass of an object. Even when all the particles within the object travel at the speed of light, some may be travelling in different directions. So the object as a whole cannot travel at the speed of light.

— Me@2023-10-22 07:37:01 AM

注定外外傳 2

Posted on October 7, 2023 by rpflee

Eternal return, 3 | Can it be Otherwise? 3

Eternal recurrence is not a useful concept.

If two periods of time are identical in all details, they are actually the same period, not two periods. If two periods of time are not identical in all details, the second period is not an “eternal return” of the first period.

— Me@2013-06-04 01:30:16 AM

「自由命定問題」的意思是問：

同一個輸入，會否只有唯一的輸出？

簡化地問：

同因是否必同果？

詳細地問：

如果第二次實驗的，所有初始設定，和第一次的完全相同的話，第二次實驗的結果，會不會和第一次的，完全相同呢？

— Me@2023-09-14 12:43:41 AM

@dialectphilosophy, 1.2

Posted on September 24, 2023 by rpflee

. . .

The meaning of “velocity is relative” is:

For example, within a car, you cannot know its velocity relative to the ground without seeing outside. In other words,

You cannot know the velocity of A (car) relative to the B (ground) without seeing B (outside).

It is because any two individual objects within the car, if both initially at rest relative to the car, have a constant separation. Also, any individual objects inside the car and any point of the car itself has a constant separation. And here is the proof:

The separation between any 2 objects within the car is

$\displaystyle{ \begin{aligned} &x_2(t) - x_1(t) \\ \end{aligned}}$

$\displaystyle{ \begin{aligned} &= \Bigl( x_2(0) + v_2 t \Bigr) - \Bigl(x_1(0) + v_1 t \Bigr) \\ \end{aligned}}$ ,

where $\displaystyle{v_1}$ and $\displaystyle{v_2}$ are velocities with respect to the ground of object 1 and object 2 respectively. If the two velocities have the same value,

$\displaystyle{ \begin{aligned} &x_2(t) - x_1(t) \\ \end{aligned}}$

$\displaystyle{ \begin{aligned} &= x_2(0) - x_1(0) \\ \end{aligned}}$

As long as object 1 and object 2 have the same velocity-relative-to-the-ground as that of the car, $\displaystyle{v}$ , i.e.

$\displaystyle{v_1=v_2=v}$ ,

no matter what value $\displaystyle{v}$ has, the distance between object 1 and object 2 is always constant. In other words, you cannot deduce the value of the $\displaystyle{v}$ by observing the separation changes between any two objects/points within the car.

Even in another case where $\displaystyle{v_1 \ne v_2}$ ,

…

— Me@2023-08-07 05:56:31 AM

Interstellar 4

Posted on September 7, 2023 by rpflee

Yes. It is Nolan. But it is drama.

Wormhole cannot be passed, physically. The past cannot be influenced by now, logically.

— Me@2015-09-28 03:23:32 PM

Standard Model equation

Posted on September 6, 2023 by rpflee

Euler problem 15.2

factorial n = facIter n 1
  where
    facIter m acc =
      if m == 0
      then acc
      else facIter (m - 1) (m * acc)

binomial n r = bIter n 1 `div` factorial r 
  where
    bIter m acc = 
      if m < n - r + 1
      then acc
      else bIter (m - 1) (m * acc)

f n = product [1..n]

b n r = product [(n-r+1)..n] `div` f r

— Me@2023-09-06 08:08:35 PM

@dialectphilosophy, 1.1

Posted on September 4, 2023 by rpflee

This post is a debug of dialectphilosophy‘s discussion of relativity.

The word “motion” in physics context should mean only velocity, not displacement, nor acceleration.

Therefore “motion is relative” should only mean “velocity is relative”. Einstein’s goal to prove that “all motion derivatives, including acceleration, are relative” is silly.
Velocity and acceleration are independent variables. “Whether velocity is relative or not” is not relevant to “whether acceleration is relative or not“.

In other words, you cannot use the value of velocity at a moment to derive the acceleration value at that moment. Fundamentally, it is due to fact that $v$ and $\Delta v$ are independent.

…

— Me@2023-08-07 05:56:31 AM

For all, 10.3

Posted on August 16, 2023 by rpflee

Adaptation

No movie can contain all the movies. At least, it cannot contain itself.

— Me@2015-10-10 07:37:26 AM

For all, 10.2

Posted on August 1, 2023 by rpflee

Adaptation

No movie can record its whole “the making of”.

Even two mutual movies [that record each other’s “the making of”] cannot work around this.

— Me@2015-10-19 06:13:58 PM

Counting of identical bosons

Posted on July 19, 2023 by rpflee

Two bosons (non-composite) can occupy the same state, including the same spatial location. When they do, they are identical.

[guess]

So, for a particular system, you cannot know the number of bosons by counting. Counting does not work when you have no way to avoid double-counting.

To distinguish among different total numbers of identical bosons, you need to check, for example, the total energy of the system.

[guess]

— Me@2015-10-12 06:16:15 PM

— Me@2023-07-19 12:11:16 PM

Visualize, 3

Posted on June 13, 2023 by rpflee

Algebra requires sequential understanding.

Geometry requires parallel understanding.

space ~ parallel

time ~ series

By the definition of “at once”, you cannot see objects or the same object at different times at once.

— Me@2016-01-04 08:44:21 PM

They don’t exist under normal condition

Posted on June 2, 2023 by rpflee

rickreynoldssf 2 days ago | next [–]

I’m an airchair physics person so I’m curious how close my layman understanding of this matches reality… So Higgs particles don’t exist under normal conditions, they’re just proof that the Higgs field exists and explains how mass exists. When the energy that’s perturbing the Higgs field dissipates it does so through other fields perturbing them to create one of their particles and so on.

Sci-Fi or Fact or somewhere in the middle?

RickyS 2 days ago | parent | next [–]

Experimental particle physicist here. What you say about Higgs particles “they don’t exist under normal condition” is loosely true of all particles in nature in the sense that a particle is nothing but a “quantum” of a “field”. Fields pervade all physical space and can vary in time. Particles (or quanta) simply represent a local state of observable things. A field can only do certain things to certain physical states and at a probabilistic level. Notice that fields do things even with the vacuum which is just another state from which particles can be “extracted”.

The peculiar experimental challenge about the Higgs field is that it can extract its quanta from certain physical states (certain initial conditions in a particle physics reaction) only at very high energy and with low probability, but that is true also for other particles. Its truly peculiar thing is that the presence of the Higgs field, in addition to the fields of all other particles that we know of, explains why quanta in general have a mass (although this is not clear for neutrinos) through a mechanism where the Higgs field interacts with the quanta of other particles.

— LHC experiments see first evidence of a rare Higgs boson decay

— Hacker News

2023.06.02 Friday ACHK

權力來源 1.4

Posted on April 17, 2023 by rpflee

這段改編自 2010 年 4 月 24 日的對話。

勢

~ environmental default

— Me@2021-11-16 07:59:12 PM

勢

~ potential

~ 未來事件s對現在的影響

— Me@2023-03-12 09:14:50 AM

potential energy

~ energy of potential motion

~ energy of future motion

— Me@2023-04-16 12:08:08 PM

權力

~ 勢力

大概而言，「權」即是「勢」。但是，兩詞給人的感覺不同。根本的原因是，它們的用法，不大相同。

「權力」著重個人，例如：「甲擁有很大的權力。」「勢」則著重外在。甲身處環境的人事心理結構，形成了一個「勢」。如果當時的那個「勢」對甲有利，就簡稱為：「甲擁有很大的勢力。」

— Me@2023-04-17 12:56:11 AM

Debugging quantum concepts

Posted on March 17, 2023 by rpflee

Reality is a superposition of eigenstates. Even if we use the pilot-wave formalism, in which a particle has definite position or momentum, the pilot wave itself is in a superposition.

— Me@2012-04-16 2:27:20 PM

Physics reality is NOT a superposition of eigenstates. If physics reality was a superposition of eigenstates, there would have never been any interference patterns.

For an experimental setup, what is in a superposition is the quantum state, which is a tool for deducing probabilities of different potential measurement results.

“A quantum state is a superposition of eigenstates” just means nothing more than that we need to use individual probabilities of the eigenstates to calculate the probabilities.

A quantum state, which is represented by a wave function, is logical, mathematical, conceptual, and linguistic in nature. A quantum state is NOT physical. A quantum state is NOT reality. A quantum state is NOT directly corresponding to a physical reality (aka observable events, measurement results, etc.)

A quantum state is NOT even corresponding to a probability directly. (If a quantum state was a probability, there would have never been the phenomenon of interference.) Instead, a quantum state is corresponding to a probability amplitude, which is used for calculating probabilities.

— Me@2023-03-16 09:57:07 AM

Intermediate states

Posted on March 2, 2023 by rpflee

What happens in the interval between the initial and final states of the interaction process?

What happens in between is everything and nothing. There is no privileged clearcut answer what happened that would be physically meaningful. It’s really the very basic point of quantum mechanics that only results of measurements are physically meaningful facts or observables; all other data are fictitious or uncertain. By the very definition of your problem, no measurement took place in the intermediate states which means that no sharp answers to any questions were generated, no answers or values became real or privileged or facts.

…

But unlike classical physics, quantum mechanics says that not only the probabilities of each history matter. All the relative phases matter, too.

— answered Jan 9, 2021 at 16:10

— Luboš Motl

— Physics StackExchange

2023.03.02 Thursday ACHK

Looper, 6

Posted on February 24, 2023 by rpflee

Causal diamonds in time travel, 3

Time travel in the absolute sense is logically impossible.

If time travel was logically possible, it still could be logically consistent from the time traveller’s point of view, as long as he cannot see from the perspective of the meta time.

— Me@2016-06-01 07:10:51 AM

— Me@2023-02-23 12:13:20 PM

Causal diamonds in time travel, 2

Posted on February 13, 2023 by rpflee

Time travel in the absolute sense is logically impossible.

If time travel was logically possible, no observer would see any paradox if there is no meta-observer, who can compare results seen by different observers.

— Me@2016-06-12 12:12:40 PM

— Me@2023-02-13 12:53:31 AM

MSI RTX 3060 Ti VENTUS 2X 8G OCV1 LHR

Posted on January 14, 2023 by rpflee

Visualizing higher dimensions, 2.2 | Remove time from physics, 2

Mathematics is local (left brain).

Physics is global (right brain).

— Me@2017-06-22 06:16:59 PM

Mathematical processes, i.e. the calculations, are local.

Physical intuitions before a calculation and the interpretations after are global.

— Me@2023-01-13 07:45:24 PM

However, in an opposite sense, physics is local and mathematics is global.

— Me@2023-01-14 08:13:17 PM

Geometry is global.

Space is what we can see at once.

Dynamics is local.

Time is what we cannot see at once.

— Me@2017-02-07 10:11:34 PM

… math is what you get when you remove time from physics.

—

Black hole mass can’t be

Posted on November 8, 2022 by rpflee

A singularity doesn’t have mass. Mass is a property of an object that exists in time. A (spacelike, e.g. Schwarzschild) singularity is not an object that exists in time. A singularity is a moment in time when time ends along with mass. Furthermore, a black hole does not have a center. The geometry of the Schwarzschild spacetime inside the horizon is an infinitely long 3-cylinder with a quickly shrinking circumference. Also, no black hole solution is valid inside the horizon, because all solutions assume a static metric, but it is not static inside the horizon.

— safesphere

— May 20, 2019 at 10:38

And if you wanted to say that the whole mass $M$ is obtained from the singularity, you won’t be able to get a good calculation because the integral over the singularity would be singular. Moreover, the space and time are really interchanged inside the black hole (the signs of the components $grr$ and $gtt$ get inverted for $r < 2GM$ ) so the exercise is in no way equivalent to a simple 3D volume integral of $M \delta(x) \delta(y) \delta(z)$ . The Schwarzschild singularity, to pick the "simplest" black hole, is a moment in time, not a place in space. It is the final moment of life for the infalling observers. In a locally (conformally) Minkowski patch near the singularity with some causally Minkowskian coordinates $t,x,y,z$ and $r = |(x,y,z)|$ , the Schwarzschild singularity looks like a $t=t_f$ hypersurface, not as $r=0$ .

— Black hole mass can't be visualized as a property of the black hole interior

— Lubos Motl

2022.11.08 Tuesday ACHK

Coherent light source

Posted on October 27, 2022 by rpflee

superkuh 17 hours ago [–]

Coherence isn’t what you think it is. It is not an “alignment in phase” of the sinusoid, like all the lay diagrams show. It isn’t even being the same frequency. In the early days of quantum physics the light sources were mercury arc lamps (muliple freqs) that achieved coherence by shining through tiny pinholes.

https://web.archive.org/web/20220820182938/http://amasci.com/miscon/coherenc.html

Coherence is being a point source. Stars, except for our sun since it is too close, are coherent light sources.

— Hacker News

2022.10.27 Thursday ACHK

Swampland

Posted on October 22, 2022 by rpflee

In physics, the term swampland refers to effective low-energy physical theories which are not compatible with string theory, in contrast to the so-called “string theory landscape” of compatible theories. In other words, the swampland is the set of consistent-looking theories with no consistent ultraviolet completion in string theory.

Developments in string theory suggest that the string theory landscape of false vacua is vast, so it is natural to ask if the landscape is as vast as allowed by consistent-looking effective field theories. Some authors, such as Cumrun Vafa, suggest that is not the case and that the swampland is in fact much larger than the string theory landscape.

— Wikipedia on Swampland (physics)

Recall that Vafa’s Swampland is a giant parameter space of effective field theories that cannot be realized within a consistent theory of quantum gravity i.e. within string/M-theory. Only a tiny island inside this Swampland, namely the stringy Landscape, is compatible with quantum gravity. String/M-theory makes lots of very strong predictions – namely that we don’t live in the Swampland. We have to live in the special hospitable Landscape.

— Vafa, quintessence vs Gross, Silverstein

— The Reference Frame