1

General Science / Re: At what gravity does a person run the fastest?

« on: 06/04/2022 16:45:48 »

Hi.

Found this:
https://journals.biologists.com/jeb/article/221/3/jeb162024/20344/Reducing-gravity-takes-the-bounce-out-of-running

A scientific study, with actual data collected, about the running stance and gait adopted in simulated low-G environments.

Their conclusions:  Mainly that the gait is adjusted so as to keep the centre of mass extremely flat and level, i.e. almost all bounce is removed.  Their models suggest this is energy efficient (they use "an impulsive model of running" developed by Rashevsky and Bekker - although these people contributed at different times and not collaboratively).
    There is no comment or investigation about the maximum speeds attainable, sorry.  However, if this low bounce method is more energy efficient you would have thought that a runner can sustain a higher maximum speed.

Noteable limitations
   They didn't seem to have a wind fan or anything to re-create the effect of air resistance.  However, you would have thought this would only further reduce speed while in the air and unable to provide propulsion with your feet, so that it would only increase the desirability of maintaining a low bounce running style.
- - - - - - - - - -
We've already mentioned that accelerating from a standing start is a completely different thing to sustaining a high top speed.   Just for amusement, here is Usain Bolt trying to sprint in low G:

Best Wishes.

2

Just Chat! / Re: Here is Practical Explanation about Next Life, Purpose of Human Life,

« on: 18/03/2022 15:55:26 »

It was nonsense last time, and it hasn't got better
https://www.thenakedscientists.com/forum/index.php?topic=75636.msg561835#msg561835

3

Physics, Astronomy & Cosmology / Re: Why don't gamma rays have a higher speed?

« on: 20/02/2022 07:47:01 »

the speed of electromagnetic propagation is based on experimental observation of the relationship between electric and magnetic fields

Maxwell's equations were a brilliant synthesis of everything known about electric and magnetic fields, producing a surprisingly accurate prediction for what we now call "c"
- I understand it was the agreement of the experimentally measured speed of light with the prediction of Maxwell's equations that influenced some people to think that light had to be electromagnetic waves.

However, Maxwell's equations do not explain why hypothetical gravitons (or the more classical gravitational waves) should also travel at "c".
- So far as we know, oscillating electric or magnetic fields do not generate gravitational waves, but do generate electromagnetic waves
- So far as we know, oscillating masses do not generate electromagnetic waves, but do generate gravitational waves (provided the masses are electrically neutral)
- And yet Einstein predicted that both would travel at "c"
- And observations of colliding neutron stars suggest that they travel at identical speeds (within very tight limits)

why does the frequency increase instead of a compromise between frequency and speed?

"c" is the velocity of light in a vacuum.
- However, in materials (eg water or optical fiber), there is a change in speed with wavelength, which is called "dispersion"
- This produces the familiar rainbow
- From Wikipedia: For red light (wavelength 750nm, η = 1.330 based on the dispersion relation of water), the radius angle is 42.5°; for blue light (wavelength 350nm, η = 1.343), the radius angle is 40.6°.
Since the refractive index η = c/v, the higher refractive index of blue light implies that its velocity is slightly lower than red light, when traveling through water. The questioner assumes that higher frequency would produce a higher velocity.

https://en.wikipedia.org/wiki/Rainbow#Mathematical_derivation

Oops - overlap with Colin2B

4

Physics, Astronomy & Cosmology / Re: Has the distance between the sun & earth changed?

« on: 23/01/2022 23:42:32 »

Im the one that asked the question; and thank you for posting this Origin.

I would like to know if this distance is a big cause of Climate change.

I see from posts that the distance does change, though is there an on going change that is climbing (a distance change or orbit change), and not staying nominal?

It can have an effect to some extent, and there are some cyclical changes in earth's orbit (see more here: https://www.fs.usda.gov/ccrc/education/climate-primer/natural-climate-cycles)

But the current (fast) changes in the climate are driven primarily by greenhouse gases (mostly carbon dioxide and methane).

We can see the effects of the cycles, as well as the recent trends (the practically vertical line at the far right) by looking at atmospheric carbon dioxide concentrations found in ice cores, the record of which goes back almost a million years (https://keelingcurve.ucsd.edu/)

co2_800k.png (110.13 kB . 1000x600 - viewed 2262 times)

5

New Theories / Re: Density Wave - Is it real?

« on: 08/12/2021 18:11:59 »

https://www.astro.princeton.edu/~eco/research/spurs/project.html

6

Question of the Week / Re: QotW - 21.10.18 - Is Dark Matter lumpy or like grains of sand?

« on: 24/10/2021 05:15:04 »

Hi,

    Ps - Mass causes Gravity, so does Momentum.
    (Equivalence)

[citation needed]
I actually googled this and got fantastic list of sites pushing bad science, but nothing that supports this.

Let's help Zer0 out a bit here.  (You don't need any help @Halc , you already know your stuff and should be confident enough already).

I think Zer0 was talking about this kind of thing:
    https://en.wikipedia.org/wiki/Stress%E2%80%93energy_tensor
The stress-energy tensor takes mass, energy and momentum as it's components.

[Diagram from Wikipedia.  See earlier link]

   Over half of the stress-energy tensor could be considered as something derived from 3-momentum and all of it is if you're considering 4-momentum.

Here's a quote from Wiki:
     The stress–energy tensor, sometimes called the stress–energy–momentum tensor or the energy–momentum tensor, is a tensor physical quantity that describes the density and flux of energy and momentum in spacetime,........... This density and flux of energy and momentum are the sources of the gravitational field in the Einstein field equations of general relativity, just as mass density is the source of such a field in Newtonian gravity.

    However, it's a bit of jump to claim that momentum is equivalent to mass.  (I mean, it just isn't in the wider sense of it but let's just confine our attention to gravitation for the moment).      Even as regards being a source of gravitation or curvature for spacetime there are limits on our ability to exchange momentum for rest mass.  The momentum of objects in space does influence the curvature of spacetime but not in the same way as rest mass would:   Just by looking at the stress-energy tensor we can see that rest mass will contribute to the  0,0  (or time-time) component of the stress energy tensor while 3-momentum contributes to other components.  So there are going to be some solutions to the Einstein Field Equations (some manifolds and metrics) for spacetime that can't be re-created by trading rest mass for momentum.  (This is not a trivial or obvious fact.   It's obvious that the solutions will be different but less clear if there would be a change of co-ordinates which make the solutions physically equivalent - i.e. the metric solutions are just tensor transformations of each other).
    I can't really be bothered to check if it might be possible to identify the different solutions you obtain as being equivalent but in different co-ordinates but I don't think we need to.  The following example seems sufficient to show one situation where we could not hope to find such a transformation.
   
    Brief example with diagrams    Consider space that is empty apart from 3 particles that are initially at rest in a line    •   •   •     That should provide us with a certain metric as a solution to Einsteins Firled Equations.  The particles will move in response to this curvature but we can see that their movement will effectively bring them together and in the natural co-ordinates in which we are regarding the situation, the centre particle never moves and we will be able to identify an event in spacetime where all the particles collide.
   Now we could reduce the mass of the centre particle  to get    •    ^•    •        and we could try and give the centre particle some momentum, possibly enough to compensate for the reduction in mass.  This may give use the same solution for the metric initially but it will only last for one instant, since the centre particle was given a non-zero momentum initially it must move relative to the other two particles and the curvature of space will change in response.  Depending on how much momentum the centre particle has and the initial direction of that momentum we can obtain drastically different results as time evolves.  For example the centre particle may come into contact with one of the particles before the other (and not both simultaneously) or it may be travelling off at some angle to the line of particles with sufficient momentum that it will escape to infinity and never coalesce with either of the big particles.  These are events in spacetime where only 2 out of the 3 particles will occupy the same space at the same time.   I can't see any way in which a change of co-ordinates would be sufficient to make the metric or the curvature of spacetime in this situation equivalent to the metric in the previous situation - but let's go slow and check it a bit more....
     The events we can identify in spacetime are fundamentally different and no change of co-ordinates can map events from one situation to events that don't exist in the second situation.  As compelling as that seems, it's not quite enough to be certain that the curvatures of spacetime won't remain the same.  All we know is that our overall systems must be physically different and not just co-ordinate transformations of each other.  The geography of the landscape might be the same even though we had different collisions between vehicles driving over the landscape - we knew the vehicles were different in mass and momentum initially anyway.  We do need to check carefully that the geography of the landscape must be different.  Since there are some significantly different events (such as when and which particles collide or occupy the same space) we can drop in a test mass at key times and see that it's movement differs   (for example if all the particles have coalesced, as in the first situation, then regardless of where you drop the test mass in, it can only be attracted to one point in space but this is not true if you're in the second situation and only 2 out of 3 particles have coalesced).  From the different movement of test particles we really can conclude that, at least at some time, the curvatures of the manifolds will be physically different and not just co-ordinate transformations of each other.

   In summary:  Mass and momentum are both sources of gravitation.  However, they are not quite equivalent, there are limits on our ability to exchange some rest mass for momentum and retain the same curvature of spacetime.  At best, we could initially obtain a space with the same physical curvature but in most situations this would not be sustained as time evolves.

Best Wishes.

(Final thoughts:  The example has turned out to be longer than I expected and perhaps I should have just gone straight for the Maths but nevermind.... most people prefer some waffle to mathematics).

7

New Theories / Re: On Kepler Orbitals For Atomic Physics

« on: 21/08/2021 23:16:08 »

The posting of this topic contravenes forum rules and has been locked

8

Physics, Astronomy & Cosmology / Re: What would happen if every neutron on Earth disappeared?

« on: 02/06/2021 22:04:31 »

Hi.

We also have to ask, what did happen to the neutrons?  By all rights they can't just disappear without leaving something else behind.  If they were suddenly converted into energy then we have a catastrophic event before we even to begin to worry about unstable nuclei that may be left behind.

9

Physics, Astronomy & Cosmology / Re: Can you measure the one way speed of light without synchronised clocks?

« on: 22/05/2021 06:23:28 »

It should be fairly easy to calculate the one-way speed of light.  The problem is doing so with any reasonable amount of accuracy.

Here's how I would do it.


SpeedOfLight.gif (9.32 kB . 669x311 - viewed 35171 times)

Light (strong laser) passes through two shaft connected spinning discs, hits a cylindrical (conical) mirror, and is projected onto a wall to record.  Mostly interested in the trailing edge of the light spot.

The shaft will twist if it's aligned with its direction of travel, so the slits won't both be at the top or bottom at the same time as each other. If you imagine two clocks at either end of the shaft with their dials aligned with the discs and with a nanosecond hand going round, the alignment of the apparatus and its speed of travel will affect the synchronisation of the two clocks, so the hands, just like the slits in the discs, will not always both be at the top or bottom at the same time, even if they are when the apparatus is at rest. Move it to the right and the clock (and disc) to the right will lag in its timing compared to the clock (and disc) to the left. This, in combination with length contraction, will always completely mask the differences you're trying to measure.

10

Question of the Week / Re: QotW - 21.04.19 - How do zip files work?

« on: 20/04/2021 11:21:24 »

"Zipping" a file saves space on your disk storage, by removing "redundant"/"not strictly necessary" information.
- Unzipping the file when it is accessed restores the missing information so the file can be read, at the cost of extra execution time.
- If you don't access the files very often, zipping them is a good way to save space, without costing you much time
- If you need to send information to someone via email, radio, podcast, or streaming video, it saves a lot of time and money to compress it first.

When I first received a laptop running Windows 10, I found it was extremely sluggish.
- I eventually traced it to a "feature" in Windows 10 which also compresses data in RAM (Random Access memory)
- Unfortunately, in a virtual-memory system like Windows 10, the data stored in RAM is there because it is frequently accessed
- So they were continually zipping and unzipping the information which is most frequently accessed
- My computer sped up a lot when I turned off this "feature"
- And sped up even more when I installed twice as much RAM!
See: https://www.howtogeek.com/319933/what-is-memory-compression-in-windows-10/

Specialised Compression Methods
There are some compression techniques that are better suited for certain types of content
- ZIP files are good at compressing text files, and can get exactly the same file back again, so it is "lossless". It is a good general-purpose compression method.
        See: https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Welch
- MP3 and AAV are specialised for compressing audio files. These intentionally drop some sound content that the average ear can't detect. What you get back "sounds" the same, but it is not exactly the same. This is a "lossy" compression.
       See: https://en.wikipedia.org/wiki/MP3
- JPEG and JPG are specialised for compressing still photographs
       See: https://en.wikipedia.org/wiki/JPEG
- MPEG and MP4 are optimised for compressing video content
       See: https://en.wikipedia.org/wiki/MPEG-4

Improvements over Time
Most of the lossy compression techniques allows the originator of the content to make a tradeoff between file size and quality of the reconstructed file.
- New video compression techniques are continually being developed which can achieve better compression ratios without degrading perceived image quality, but usually at the cost of greatly increased processing power
- If you want to move from HDTV (2k pixels) to UHDTV (4k pixels) without improving the compression technique, you will need 4x the bandwidth on your internet connection and/or 4x the storage on your portable device.
- But if you install a more powerful image processor on your display device, and use better image compression standard, you may only need 2x the bandwidth.

See: https://en.wikipedia.org/wiki/Data_compression

11

Physics, Astronomy & Cosmology / Re: Why Didn't Einstein FULLY Address Simultaneity-at-a-Distance?

« on: 14/04/2021 23:48:34 »

So I wouldn't waste time trying to take a picture of it.

How about you stop wasting our time by posting your nonsense in the main part of the forum.
Feel free to post your ‘theories’ in the appropriate section rather than here, otherwise you might find your ability to post in the main sections limited.

If it were left to you Hertz would have been told to ignore the meter reading and forget that radio waves might be discovered.

12

Physics, Astronomy & Cosmology / Re: Our solar system in relation to universe expansion?

« on: 06/03/2021 15:18:15 »

@Halc
😊
🙏

Hmm...Your detailed description has allowed me to finally Unwrap my head around that " Aether " hypothesis.
👍

Say...why would you want to pull ur car bumper off even if u could...lol
Anyways, does it have that " sh1t Happens " logo on it?
🤔

And ofcourse, when it comes to jumping inside a blackhole...i gotta do it yes...wow! Ur a meanie!
😏
Anyways, I'm familiar with " Sphaggetification "...is that even a word?
🤔

New stuff i learned...Sgt A does hold on slightly but it's the mass of the whole Mway(22000) times that helps keep it in shape.
👍
Did You know the Earth accelerates  & deaccelerates while moving around the sun in the ecliptical orbit...cool Right!
😎

Anyways, why have such different shades of User levels...perhaps it just encourages a few to keep blabbering n posting randomly inorder to level up.
🤔

& say...just having a nicknamed Zer0 wasn't blunt enough eh!
So perhaps i should change that being human stuff...
Yep!
It might suit me, but it does Not help me...
Tanks 4 d Idea!
😉👍


P.S. - Thank You Very Much for explaining things soo Nicely.
🙏
Next time when you sleep or doze off, go down with a smile on ur face thinking U made a difference in this world...a positive one that is.
🖖
Regards,
0.

13

Physics, Astronomy & Cosmology / Re: Sun-synchronous orbit spacecrafts

« on: 05/02/2021 20:52:10 »

He seems to be referring to a Solar-synchronous orbit.   This is a polar orbit which precesses at a rate equal to a Solar day.

Ah, I was picturing something that hovered over one point on the sun, for some unfathomable reason. This is something orbiting Earth, not the sun.

How do they get a polar orbit to precess all the way around once per year? Expend energy?
Seems like it would be at geosync altitude on average, but different orbital axis.
It need not be a circular orbit at all, and would benefit from being furthest from Earth in the day to give more time to measure stuff. Such an eccentric orbit also keeps it out of the high-contention geosync path.

They fine tune the inclination of the orbit according to its altitude ( in other words, it is not a perfectly polar orbit).  That way, the Earth's own equatorial bulge produces the desired precession.  Solar synchronous orbits are not put at geo-sync altitudes.  They are much lower.  They can orbit the Earth multiple times a day. (for weather and surveillance satellites this means you can image multiple points on the Earth's surface)  You just want consistent lighting for any given region on every pass.

14

New Theories / Re: Was the light speed problem really solved by Einstein in 1905 ?

« on: 05/01/2021 11:56:04 »

    Was the light speed problem really solved by Einstein in 1905 ?

 Einstein did not truly succeed in eliminating the ether, and Einstein himself never realized this. Few, if any, physicists realize this. The ether always haunted the thinking of the physicists.

Then you haven't studied Einstein much.

"More careful reflection teaches us, however, that the special theory of relativity does not compel us to deny ether."
 -Albert Einstein

"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it."
 -Albert Einstein

You can easily find the full text by searching for...

Albert Einstein - Ether and the Theory of Relativity, 1920

15

That CAN'T be true! / Re: I don’t understand physics: does anyone understand physics these days?

« on: 30/12/2020 01:35:12 »

Appealing to statistics is the last refuge of incompetent Physics

This is beginning to more and more like a simple "sour grapes" attitude.  Modern physics has grown beyond your understanding, so you you respond by claiming that modern physics isn't worth understanding.

16

General Science / Re: Is Wikipedia's entry on Prime Number Theorems wrong?

« on: 19/11/2020 20:27:00 »

Without having calculated it myself, I can see that both can be true.

Approximation (as n→∞)
First, Wikipedia give two approximations to π(n)= "the quantity of prime numbers <n"; one approximation converges much more quickly than the other.
- The poorer approximation π(n) ≈ n/ln(n) always estimates too high (for n>100 or so)
- The better approximation π(n) ≈ ∫1/ln(t) estimates too low (for n=100 to 1,000,000), but is fairly close above that

lim_n→∞ π(n)/∫1/ln(t) = 1

The first statement is a measure of Relative Error.
It says that if you take these two very large numbers (approaching infinity), and divide one by the other, the answer approaches 1. So the Relative Error approaches 0 as n→∞.

∫1/ln(t) - π(n) has infinitely many sign changes

The second statement is a measure of Absolute Error.

Since the density of primes is very low when you get to large n, (the graph shows n up to 10²⁴), prime numbers get very rare. The function π(n) spends most of the time unchanged as n increases. But when it hits another prime number, it will suddenly jump up by 1.

In contrast, ∫1/ln(t) always increases, even when n is not a prime. That means π(n) will sometimes be above it, and sometimes below it. And since there are an infinite number of primes, that "sometimes" is an infinite number of times.

That tells you that ∫1/ln(t) is a pretty good approximation (provided n > 1 million or so).

Perhaps more mind-bending, they also say that the maximum Absolute Error of ∫1/ln(t) grows without limit as n→∞.
- However, this Absolute Error grows much more slowly than π(n), so the Relative Error is infinitesimal.

Here is the link where this is discussed: https://en.wikipedia.org/wiki/Prime_number_theorem#Statement

17

New Theories / Re: Can heat affect Earth's rotation?

« on: 24/09/2020 19:48:49 »

That leads to the angular velocity 'w (omega)' change because L=I*w and L is 'constant'.

You have accepted that L is constant, as part of your "proof" that L changes.


Were you expecting to be taken seriously?

18

Physics, Astronomy & Cosmology / Re: What happens when both slits are observed by in the double slit experiment?

« on: 07/11/2019 13:25:35 »

You really need to abandon the particle/wave duality business to make progress in physics. Photons, atoms, indeed everything, behaves as it does because it is what it is, not what you choose to model it as.

Quantum mechanics gives us an excellent predictive model of the behaviour of very small things, but doesn't say what they "are". Continuum mechanics gives us an adequately predictive model of mesoscopic entities that allows us to build houses and fly to the planets. The important question to ask of quantum mechanics is "does it scale up to the observed behaviour of radio waves and billiard balls?", which it does. Likewise the test of relativity is "does it scale down to Newtonian mechanics if v<<c?", which it does.

The problem with poking a particulate photon through two slits is manifold.

1. Only half the energy can go through each slit, so the wavelength of the emerging "photons" will be twice as long - but it isn't!   

2. If we rotate the receiver, we will alter the time at which the two bits of photon reach it, so they can't interfere - but they do!

Equally, however, if we presume a wave passing through both slits, all the interference peaks will occur simultaneously, however weak the source (down to one photon at a time) - but they don't!

It gets even more exciting when we pass "solid" objects like electrons, atoms or buckyballs through a diffraction grating. There's no way they can disintegrate and recombine at the receptor (if we move the receptor further away, where does the recombination happen?  If we remove it altogether, have we created partial electrons wandering through space?) but they form the predicted pattern!

The answer: believe what you see, and choose the most appropriate model to predict what you might see next time, but don't be surprised if something else happens - it just means your model was incomplete.

19

Just Chat! / Re: I am not a timetraveler

« on: 10/03/2019 20:20:12 »

Another option is to shout " There is free beer in Rome", then follow the crowd.

20

Physics, Astronomy & Cosmology / Re: Why can't we recycle the water in our breath?

« on: 12/09/2018 21:50:10 »

Absolutely standard procedure where it is necessary to do so artificially (spacecraft) - air conditioning and urine recycling plant conserves water as far as possible. On the surface of the earth, all the water vapor eventually finds its way into a cloud, then rain, river, and back to the tap via the usual filters: 100% natural process driven by the sun.