1

General Science / Re: How are rainbows made?

« on: Today at 01:12:29 »

As a kid, it was my favourite time to watch a rainbow come up and wait until it disappears.
But I never understood how they were made.
And if there is really a treasure at the bottom...

Rainbows are caused by the fact that light has it's path bent when passing through water droplets. Sunlight is a mixture of light in all the visible colors.  These different colors of light bend by slightly different amounts when passing through the droplet.  This breaks the Sunlight up into it constituent color.  This causes you to see all these colors separately as a rainbow.
Seeing a rainbow relies on the angle of where the sunlight in coming from and the angle between your eye and the droplets forming.  Because of this rainbows always appear to keep a constant distance from you.  If you walk towards it it retreats from you.
So, you can never reach either end of a rainbow to get to the promised treasure. The phrase, " The pot of Gold at the end of the rainbow" is more meant to express the idea of an unobtainable goal or reward. Something you can never get.

2

Geology, Palaeontology & Archaeology / Re: Is the earth really flat?

« on: Today at 00:55:32 »

Hey guys,
it's an old topic and a am really not a flatearther.
But it's indeed a good question how the water stays on the round earth.
It should just fload down from the planet, right?

Because "down" is defined by gravity and the Earth's gravity acts toward the center of the Earth.  Water tends to, if it can, flow "down hill", and "downhill" means closer to the Earth's center. (Of course, it can't flow all the way to the center because the bulk of the Earth gets in the way.)

3

Geology, Palaeontology & Archaeology / Re: Somebody explain please

« on: Today at 00:41:40 »

Gravity.

Which is also why the atmosphere clings to the Earth, and why we aren't flung into space by its rotation.

4

General Science / Re: How far away is the sun?

« on: Yesterday at 21:12:29 »

Put in other terms:
You could fit about 30 Earth's between the Earth and the Moon, and the Sun is 400 times further away than that.
At this distance, the Earth only intercepts 0.000000045% of the light and heat put out by the Sun, and even that small fraction is 173,000,000,000,000,000, watts or 100,000 times the total world energy usage.

That being said, the surface of the Sun is  just ~5,500̊ C or a bit shy of 10,000̊ F

5

Physics, Astronomy & Cosmology / Re: Why is time going slower?

« on: 27/02/2021 20:50:39 »

Thanks. I understand what you are saying, but am not getting the same answers. When I use T = T₀ / √1-(r_s / r), I get 1.0000000215855072659 for Mercury. I am using km in that equation for r_s and r. In the GM equation I am using m for r_s and r as G uses m. Is that correct?

OK. I see what I was looking at wrong. To the distant observer, Mercury is .0000000215855072659 slower. It relates to the distant observer, not the Sun.

But, why am I getting different answers than you? I am using 2.5 for r_s and 5.7909227*10⁷  for r for Mercury.

5.7909227 e7 is the orbital radius in km

My mistake.  I was plugging the numbers in by hand into a calculator, and neglected to take the square root before inverting.

6

Physics, Astronomy & Cosmology / Re: Why is time going slower?

« on: 27/02/2021 16:44:02 »

My understanding is that time goes faster with altitude, but when I work the time dilation formula for gravity, T=T₀/√((1-(2GM/Rc²)), the dilation factor gets smaller as R increases, so time appears to go slower. I get less s/s difference at Neptune than I do Mercury. For Mercury I get 0.9999999745 and the #seconds is 1.0000000254 and Neptune is 0.9999999996 and 1.0000000003. Shouldn't I be getting a bigger s/s difference if time accelerates with R?

In this equation, T is the amount of time it takes for a far removed observer to measure a time of T₀ pass for the clock deeper in the gravity field.  So for example if T₀ is one sec ticking off on an clock sitting on the surface of the Earth, then T is how much time it takes for our observer to see the Earth clock tick off that second.
So using the equation for a Earth surface clock :
T = 1.00000000069 sec if T₀ = 1 sec
It takes that much more than 1 sec for our observer to measure the Earth clock tick off just one sec, ergo, the Earth clock ticks slower than his.
He looks at a clock higher above the Earth's surface(let's say 2 Earth radii above it)
then  T = 1.00000000023 sec if T₀ = 1 sec.
This means it takes him not quite as long to measure this clock tick off 1 sec than it does for the the surface clock.
He measures the higher clock tick off secs faster than the lower clock, and the higher clock ticks faster than the lower one.
For Mercury and Neptune (computing time dilation due to orbital distance from the Sun), I get
1.000000051 for Mercury
1.00000000065 for Neptune.
It takes a longer time for our observer to measure Mercury's clock tick off one sec than it does for him to measure Neptune's clock tick off one sec, thus Neptune's clock ticks faster at its greater distance from the Sun.
All is in order.

7

Physics, Astronomy & Cosmology / Re: How do we determine the value of time dilation?

« on: 26/02/2021 17:10:23 »

Galileo, you're suggesting that a time dilation only belonging to GR, if I read you correct?

No, he isn't. It is a misconception that SR cannot deal with acceleration and you need to invoke GR to deal with it.  GR is only needed if you introduce gravitational effects

Would that be true then relativistic Doppler effects shouldn't exist. There is no 'acceleration' to light, only a propagation at a set speed. You have emission and absorption, red and blueshifts, but no acceleration.There are other arguments and examples but that one should be sufficient.

" The relativistic Doppler effect is the change in frequency (and wavelength) of light, caused by the relative motion of the source and the observer (as in the classical Doppler effect), when taking into account effects described by the special theory of relativity. The relativistic Doppler effect is different from the non-relativistic Doppler effect as the equations include the time dilation effect of special relativity and do not involve the medium of propagation as a reference point. They describe the total difference in observed frequencies and possess the required Lorentz symmetry.

Astronomers know of three sources of redshift/blueshift: Doppler shifts; gravitational redshifts (due to light exiting a gravitational field); and cosmological expansion (where space itself stretches). "

It is really important here to distinguish between "time dilation" which is the difference in clock rates measured between relatively moving frames of reference, and the "total difference in time accumulation" demonstrated at the end of the Twin Paradox scenario.
During the outbound and Inbound legs of the Trip, both observers measure the other observer as being time dilated. However, they both agree which one of them aged less during the period when they were separated then reunited.

And, as far as acceleration is concerned, it is required for the Twin paradox, as it is the only way under SR that the two twins can separate and then reunite* And which twin accelerates in order for them to reunite determines which twin will have accumulated less time upon their reuniting.

As far as acceleration and Doppler shift goes:   Like time dilation, Relativistic Doppler shift is a measurement made between an observer and a relatively moving source.  If we are moving apart, you see my light as being red-shifted and I see your light Red-shifted.  If we are moving together we see each other as blue-shifted.

But even here acceleration does matter with the Twin Paradox.
So for example: Twin A and Twin B separate at 0.6 c to a planet 6 light years away ( as measured by A), B then accelerates to return to A.
A starts off measuring a red-shift from B with a factor of 0.5  Now while it takes 10 years for B to get to the turn around point, A doesn't See this until  6 yr later.  In other words A sees that red-shift from B for 16 years, seeing B age 0.5x16 = 8 yrs
Then A sees B become blueshifted at a factor of 2.  Since B takes twenty years to make the round trip, this leaves just 4 years for A to see B blue-shifted, and see him age another 2*4 = 8 yrs for a total of 16 years during the 20 yrs he was gone.
B on the other hand see A red-shifted as they separate ( also at a factor of 0.5). It takes 8 yrs by his clock to get to the planet which is 4.8 light yrs from A ( length contraction) by his measure. During this time hes sees A age 0.5 x 8 = 4 yrs. 
He then accelerates to start the trip back ( assume negligible time spent accelerating).  He immediately sees the light from A go to blue-shift**  to a factor of 2.   It takes 8 yrs to meet up with A again, during which time he sees him age 2 x 8 = 16 years for a total of 20 years for his 16.

There is nothing contradictory between acceleration being required for the Twin paradox scenario and the observation of Doppler shift, and your criticisms of Galileo's statements are unfounded.   

* And they do have to reunite, as this is the only way that you can objectively say that one twin accumulated less total time.

** while A had to wait 6 years to  see the Doppler shift change due to B accelerating, this is because the change was the result of something happening 6 light years away.
B sees the change instantly because it is the result of what he himself is doing.

8

Physics, Astronomy & Cosmology / Re: Is a unit of energy the same, no matter how it is produced?

« on: 25/02/2021 00:02:18 »

Please name a unit of electrical energy that is not a unit of any other form of energy.

How about "volt"?

A volt is a measure of electrical potential.
It, pushing current through a 1 ohm resistance  results in 1 watt (Volts x Amps*), a measure of power, which over a duration of 1 sec, gives a watt-sec or 1 joule of energy.

* If you are dealing strictly with DC current or AC current with a purely resistance load. Otherwise, you have to consider the Power factor caused by either inductance or capacitance in the circuit.

9

Just Chat! / Re: Does Dark Matter influence Atomic Matter?

« on: 23/02/2021 20:56:47 »

Just chatting ( and rambling on ): (Just Chat allows?)
Probably the type of mass involved in dark matter has nothing that spins and thus cannot set up proper energy levels and thus has only a ground state susceptible to energy fluctuations......Perhaps spin is time dependent and dark matter formed after atomic matter when things cooled beyond what spin required?....

"Spin" has nothing to do with it.  The neutrino has a spin of 1/2 and  is basically a type of "Dark matter". It has a mass but does not interact via the electromagnetic interaction.  It would be the type of Dark Matter known as a WIMP ( Weakly Interacting Massive Particle.) 

10

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 17/02/2021 18:09:52 »

When we bowed light, we did not have lasers.  We used a flashlight.  White light.  Bowed white light.  Full of phase and wavelength.

And, if you had looked closely at the edges of that bowed wide light, you would have seen colored fringes caused by chromatic aberration, where the different wavelengths that make up "white" light where bowed by differing amounts.
You won't see it in the main beam because the all the different colors are still there and mixing, which it why it is only noticeable at the edges.
However, when looking at something like the light of a star bending as it passes the Sun, it doesn't act like a broad beam, but like a point source, and the chromatic aberration would be more noticeable if the bending was caused by interaction with a medium.

11

Physics, Astronomy & Cosmology / Re: Should we use light years for distances

« on: 17/02/2021 17:49:38 »

I just read an article in Scholar Journal of Applied Sciences and Research that clarified the meaning of the term "proper distance" rather well so I now understand.  Ain't education a great thing - I'm 77 and I haven't stopped learning yet.  Forgive my layman approach.  My speciality is fine art but my interest is cosmology.

On Dark Matter I'll leave you with the thought that science had space full of "ether" as a transmission medium for a long time before before it was determined that waveforms could also be particles.  No-one had a better theory at that stage of knowledge so they had to invent ether.  Sound familiar?

That's not what happened.  What happened was that when we started to make observations and do experiments to detect the "ether", they all failed to do so, even when they should of.( IOW experiment X should have produced result B if there were an ether, but it didn't)  It had nothing to do with the fact that light could have particle-like properties.
With dark matter we have also continued to make new a better observations.   Again, it was a matter of  "If dark matter exists, then we should be able to find situations where observation A occurs.  We look for such a situation, and lo and behold, we find observation A. 
So what has happened is that as we have increased our observations, other explanations have been falling to the wayside, while dark matter still hangs in there.  If anything, observations have, to date, strengthened the case for dark matter.

The other difference is that the ether model had other problems, the Ether had to have a a set of almost contradictory properties.
This is not the case with DM,  DM just doesn't interact electromagnetically.* 
The point being is that pretty much everything about "normal matter" that gives it the properties we can measure is due to its ability interact electormagnetically.   We see it because of that,  We can touch and hold it or bounce stuff off of it ( all due to electromagnetic interaction) etc.  Remove that ability, and all that goes away.
And it not as if we don't already have an example of a particle that behaves like dark matter in this way.  Neutrinos are particles that have mass and yet do not interact via electromagnetism.  Billions of them pass right through your body every day without ever interacting with it.

* Which in effect, makes it simpler than what we consider "normal matter".  And generally, the simpler things tend to be more abundant than the more complex ( For example Hydrogen, the simplest of atoms, by far the most abundant in the universe).
So, one would think, that being less complex than "normal" matter, one might expect that dark matter would be more abundant, and this seems to be the case.   
So maybe it isn't dark matter that is odd, but it is  the so called "normal" matter that is the outlier, with its "extra" mode of interaction that allows it to form complex structures like atoms, molecules, etc.   Maybe the only reason we think of it being the "norm" is because we are made from it and we are just being baryon-centric in our viewpoint.

12

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 16/02/2021 18:06:44 »

I am also no big expert on this topic. Just an enthusiast as to how everything in life works. Furhtermore trying to just seek out a logical explanation for almost everything in life 
I recall seeing in a couple of videos on YouTube that light ist bent by objects.

Is or isn't? 
also, one needs to be careful when getting information from YouTube videos, as there is a lot of incorrect information out there.
as far as light direction being changed by objects.  There are a few ways this can happen:
Reflection.  Light bounces off the object.
Scattering. light is effected by passing through an object or medium by interacting with the individual particles within it.
Refraction,  The light path direction is changed by passing through the boundary between mediums of different refraction indices. (or through a medium with a changing index of refraction.
Defraction. Light path is spread by passing through a slit or close to the edge of an object

With all of these, with the exception of reflection, the degree of path change is dependent on the wavelength of the light.
Thus, they would produce a measurable separation of the component colors in white light.

With gravitational lensing, you would not see such a separation of colors. The path of all frequencies would be changed equally.

This is where all these alternate explanations for the bending of light as they pass the Sun or distant galaxies fail.  These other suggested mechanisms would produce other noticeable effects in the light that we just don't observe. *

* Plus, in the example of our own Sun, it would be take the greatest of coincidences for these effects to cause the exact amount of bending as predicted for gravitational lensing. 

13

Physics, Astronomy & Cosmology / Re: Should we use light years for distances

« on: 16/02/2021 17:30:52 »

Cosmological distances are expressed in terms of how long the light takes to reach us because the speed of light is constant in a vacuum.  Yet we know that the speed of light varies considerably if it passes through anything but an empty vacuum and has even been stopped and restarted in laboratory experiments.  Is it inconceivable then that, in 13 billion years (less for nearer objects), the light has never had to pass through anything that would affect its speed?  I put this to the team that managed to stop and restart light and they smugly replied that their artificially created laboratory experiment could never occur naturally.  So their laboratory conditions didn’t comply with natural laws and couldn’t occur elsewhere in 13 billion years?  And that’s without the presence of “dark matter” which is assumed to be 85% of all matter and to pervade space.  Hardly an empty vacuum then.  If there is any question over the time light has taken to reach us, maybe the cosmos is not the size we think it is.

While a light year is defined as the distance light travels in a year in a vacuum. This is just a definition. ( in fact, the year used is not even the calendar year of 365.24219 days but the Julian year of 365.25 days)
.
We do not use the time in which it takes light to reach us from some distant star or galaxy to determine its distance, because we have no way of measuring that.  The light year is just a convenient unit of distance like a mile.  Just like a mile (5280 ft) is more  convenient measure when it come to the distance between towns than ft, a light year(9,460,730,472,580.8 km) is a more convenient measure for the distance between stars or galaxies than kilometers.

We use other ways to measure the distances, parallax*, the known relationship between luminosity and period for Cepheid variables, etc. 

We then just use out predefined "yardstick" of a light year to express those distances.

Also, it must be noted that all such measurements will have a certain amount of measurement error that is taken into account.
So even with our closest neighboring star, our best measurement of its distance can be off by a range of 17 light days or about 5% of a light year.
The Andromeda galaxy is listed as being 2.54 million light years away, give or take 110,000 light years, as another example.

The point being that when making these distance measurements, they do take into account those factors which could create errors in the measurement.

* Parallax measurements also inspired a "yardstick" of its own, the Parsec,  which is the distance at which an object needs to be to show 1 arcsecond of parallax.  (you'll also see stars distances given in mas or milli-arcseconds, which is a direct parallax measure, which then can be converted to a distance measurement if needed.

14

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 15/02/2021 20:35:31 »

I could look up what sugar-water is, but decline to do, as it doesn't seem of any real relevance.

The point I was making is this: refraction of light through the lens-shaped dust clouds which surround distant galaxies, could explain the image displacement effects which we observe from Earth.
 
How can you confute this reasonable suggestion.  When even a glass of water, observed at close quarters, can make a straw look bent, when it actually isn't.  I rest my case.

And if you look really close at that pencil, you will not a fuzzy rainbow effect at its edges.  This is the chromatic aberration that Bored Chemist brought up.   When light is refracted or even scattered, different frequencies of light have their paths altered by different amounts (This is why a prism can break white light up into is component colors.)

The fact that light passing by galaxies shows no sign of this effect indicates that refraction or scattering cannot be the cause.
And to reiterate Bored Chemist's remark:   Why do you think that scientists wouldn't have ruled out already known effect before coming to the to the conclusion they did?
If you thought of it with your limited grasp of science, why wouldn't had they?
What is it that makes you think that the professional scientists that study these things are so incompetent that hey couldn't find their backside with both hands?

Why do you think that you can see things they can't?

The only reason I can come up with is misplaced hubris on your part.

15

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 15/02/2021 06:10:56 »

I don't think the mathematical model was "lucky" or "fudged" - it just followed the evidence
- The part where Einstein did find out he had fudged the result was in picking a value for the cosmological constant to fit in with the common view at the time (stretching all the way back to Newton, and probably to Greek philosophers) that the universe as a whole (outside the Earth & Planets) was static and unchanging.

A couple of points.  Einstein tended to approach things a bit differently that other theorists.  While they would start from the experimental evidence and work back to a theory to explain it, he tended to start from basic concepts and assumptions, follow them to their logical conclusion and see if it matched the evidence.  Pretty much the opposite of "fudging".

The other thing to consider with his cosmological constant was that, at the time, he developed GR, it still had not been established that the universe extended past the Milky way.  So not only did he not know of  the expansion, but he was considering a much smaller "universe".

16

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 14/02/2021 17:44:40 »

Cannot see that gravitation has anything to do with the deflection of light as the beam is totally mass-less?

You are intermixing 2 different physics models here; Newtonian and Relativity.
Under Newton, gravity is an attraction between masses, using the Newtonian definition for mass.
With Relativity, gravity is coupled to the Energy momentum tensor, of which the Newtonian concept of "mass" is only a single component.
Classical Newtonian mass is what Relativity would call rest or Proper mass.
Thus when it is said that light is massless, we means it has no proper mass.   However, it still has energy, momentum* etc, which are other components of the energy-momentum tensor through gravity couples.

So under Newton, gravity only relies on the "mass", while under Relativity energy content also plays a role.

The point is that you can't use the gravity model and definition of "mass" from one theory and expect it to make sense if you apply it to a theory that uses a different model.

* and while the Newtonian definition of momentum is p= mv, momentum of a photon is related to its energy by p = E/c

17

Physics, Astronomy & Cosmology / Re: Why is light bent whent it passes a massive body in the space?

« on: 14/02/2021 15:39:36 »

How can it be measured.

One way is to measure (with a tape measure) the diameter of Earth, and then its circumference.  This isn't practical of course since you can't pass a tape measure through Earth, and it is hard to line up if held off to the side, but if you did, the circumference would definitely be less than the diameter * π.  This can only be explained with non-Euclidean spacetime, and is quantified precisely by Einstein's field equations.

The difference isn't much with Earth, but it is for more massive things like neutron stars.

Actually, I'm sure the size of the Earth can me measured during a lunar eclipse, when the Earth's shadow is cast on the Moon. Due to the vast distances it can be assumed the rays are parallel.

Nowhere near to the accuracy needed to note the effects discussed.  In this case "nearly parallel" isn't good enough, especially when combined with the fact that the Sun isn't a perfect point source, which means the edge of the shadow it casts will be a bit fuzzy.

18

Geology, Palaeontology & Archaeology / Re: Bones of animals in the ground

« on: 11/02/2021 17:12:45 »

How likely is it that you are in some place in the world and there are no animal bones underneath you? No matter how deep under the earth they are. But I mean actually still more or less intact bones and not oil. Also fossilized bones or remains are OK. As many animals as there are, would such a place have to be impossible, or do I think in wrong scales and there are not so many animals as I think that their are?

Bones break up and decompose over time. In a typically humid environment, in a decade or a bit more.  This means most bones decompose before ever being buried very deep.    It is only under unusual conditions that they last longer.  In arid dessert conditions, or if they end up being encased in a way the protects then from the microorganisms that would break them down.  So, in most places in the world, you would be able to dig down and never come across intact bones.

19

The Environment / Re: What would happen if all of humanity vanishes in one second?

« on: 11/02/2021 16:52:32 »

What would happen if all of humanity vanishes in one second? Like just vanish and leaf all of our buildings and so on, but not our decaying bodies.  Would that stop the  climate change in an instant, or are we too far along by now? Would the rainforest slowly grow back, or is it lost forever? Can almost extinct species come back and repopulate areas where humans used to live instantly?

Look up a book called: "The World Without Us"  by Alan Weisman
It covers this exact subject.  It starts from the time at which we disappear, and goes and extrapolates forward from there over time.

20

Physics, Astronomy & Cosmology / Re: The explanation of the darkness of the sky to the space between Earth and Moon

« on: 10/02/2021 04:01:40 »

Explanations of this as due to refractive effects in the Earth's atmosphere, don't seem entirely convincing.

I wasn't aware anyone would have tried. The blood moon effect is due to  scattering.

Isn't "scattering" another word for "refraction"?

No.  Refraction is caused by light passing form crossing through a surface that defines two regions with different light propagation speeds ( like when passes from air to glass and back to air again.
Scattering is caused by the light interacting with individual particles as it passes though a medium.

Here are 4 cubes, two large and two small.
The left ones show refraction and the left ones scattering.

scatter.png (345.97 kB . 940x529 - viewed 297 times)
 
With the refraction cubes, the size doesn't effect the refraction, just the angle the light passes through the faces.
With the scattering cubes, the volume effects the scatter, the larger cube scatters more light because the light has to pass through a larger volume.