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Posts posted by Janus

  1. 1 hour ago, Otto Nomicus said:

    You did get it work out, and without complicated equations involving squares, well done. The only reservation I have is that the velocity of the clock along its horizontal path had to be distorted for it to work. I understand the logic behind it, that the light beam was perceived as completing a longer path than 1 m during the cycle and that was used as the basis for gauging the clock's velocity, assuming that the beam had traveled that path at normal light speed so it took a longer time, thus the clock must have traveled a shorter distance relative to the cycle time.

    What if the clock were traveling along a track set up in a lab of sufficient size and we could gauge its velocity along that track? We would find that it moved 0.866 m in the time the light took to complete its cycle, because the light beam really only moved the vertical height of the clock, not a slanted path. A laser beam doesn't propagate on a slant when directed vertically, because somebody would have noticed if it did. Why, then, would it be assumed that the beam had traveled a longer path simply because the clock moved horizontally at the same time? I don't think that's logically plausible. By that logic, if you dropped an object from a certain height and simultaneously threw another matching object horizontally then the one one dropped straight down would hit the ground before the horizontally thrown one, which is not actually the case. Do you consider the thrown object to have traveled a curved path to ground at a greater velocity than the dropped object traveled straight down, or do you just consider it to have traveled horizontally at a certain velocity at the same time as traveling vertically at the speed of gravity? It was two different velocity vectors, not one.

    The clock moving horizontally is a similar situation, the light waves moved straight down at 1 c while also moving horizontally at 0.866 c, or at least appearing to move horizontally, but it's velocity was not actually a combination of the two, which would mean it exceeded normal light speed and was therefore seen as requiring correction to bring it back down to normal, using velocity contraction and time dilation. There was never a need for correction because the photons had never traveled any farther than 0.5 m up and down vertically, totally a round trip of 1 m, at a velocity of 299,792,458 m/s.

    Now there's the question of whether the light waves/photons were actually inheriting the horizontal motion of the emitter after being emitted vertically. That would make it like a ball tossed vertically by a person on a moving train. What causes the ball to keep moving with the train after being tossed? The obvious answer is inertia. Does light possess inertia? How could it when inertia is a property of mass and light has no mass? So were the vertically propagating light waves really ever moving horizontally with the clock or was it an illusion? One thing is certain, the light was never propagating on a slanted path.

    It appears that the moving clock should have been considered as if it weren't moving at all, in which case, photons would not be required to possess inertia to explain the situation. The obvious conclusion is that, when observing a moving frame with a vertical light beam in it, you should consider the situation to be that you see the light clock exactly as you would if neither of you were moving, no time dilation involved whatsoever. If you see the situation that way then how could you see the situation differently if there were two beams in the moving frame, one vertical and one horizontal? You couldn't use time dilation for the horizontal beam and not have it also effect the vertical beam, which never required time correction at all. So how is time dilation a real thing? Maybe muons just decay more slowly when accelerated, how would you know that wasn't the real explanation for muons making it to the earth's surface? Their mass would supposedly be increased, that theory may be valid, and maybe their rate of decay is slowed in direct proportion to that mass increase. That would remove the most popular proof cited for time dilation and length contraction being valid.

    To your point of a laser beam propagating at an angle, It does.  This is a well understood concept called the aberration of light.  If I put a laser on a moving cart, aimed straight up, and the cart is moving relative to me, I would measure the laser as propagating at an angle other than straight up.  Of course since the speed of light is as fast as it is. the cart would have to be moving at a pretty good clip for me to notice it without very accurate measuring equipment.

    A lot of the rest of your post revolves around motion, and appears to treat it as an absolute.  It is not.  This is something Galileo understood.

    The "Moving clock" can considered to be at rest, and the "observer" as moving.  It doesn't matter which of the two you consider as moving, the observer will observe the same thing.  Relative to himself, the light travels at angle.  The total distance traveled as measured by them, is longer than that measured by the clock.  A postulate of SR is that light travels at c relative to frame of reference from which it is being measured.

    Here's an animation comparing 2 light clocks, one moving relative to the frame, the other not. The white dots are the light pulses bouncing between two mirrors. The circles expand at c to represent the speed of light.


    Now as far as the moving clock is concerned, the it's pulse just goes up and down between the  mirrors at c, so it measures 1 "tick" to last the same length of time as the non-moving clock does in this animation.  So for example, both clocks would measure going from 0 to 1 as taking 1 us.

    For a horizontal pulse, you need to take length contraction into account, as the
    stationary clock would measure the moving clock as being length contracted:


    You will also note that as far as the stationary clock goes, the horizontal pulse going in one direction take longer for the moving clock. This is an example of the Relativity of Simultaneity.

    Also, if we were to switch our viewing frame, so that we saw the clock moving to the right as "stationary" and the other other clock moving to the left. Then it would be the clock moving to the right that would be seen as ticking slower (keeping in mind that we change nothing but which clock we are "following")

    As far as muons go, their "mass" does not increase.  Their kinetic energy is high, and thus their momentum. But what is really happening is that the increase in both rise at a different rate than that predicted by Newtonian physics.  So, if you were to apply Newtonian formulas to them, it would seem as if their mass increased, but the Newtonian formulas don't apply properly here.

    Besides that, the muon example, while one of the earlier tests of Relativity, was not the only and definitely not the last.  Countless of observations have been made, all giving results affirming Relativity.  You would have to come up with multiple explanations for them all. Explanations which conspired to produce the results of Relativity.

  2. Newtonian Physics says the period of an orbiting object is T = 2pi R^(3/2)/(GM)^(1/2)

    Thus 1/(2pi) = R^(3/2) / T(GM)^(1/2)

    Square both sides:

    1/(2pi)^2 = R^3 /  GM T^2

    Move GM to the left side of the equation:

    1/GM(2pi)^2 = R^3 / T^2

    Invert both sides

    GM(2pi)^2 = T^2/R^3

    So what Kepler's law states is that for any central body, there is a specific relationship between R and T

     Newton keeps the relationship.   It just includes the mass of the central body, so if you know any two of T, R, or M. you can find the third.



  3. Dark energy is not required for the universe to expand, it is needed to explain why the rate of expansion has been increasing over time.

    The original assumption was that, starting from some initial impetus, the universe began to expand, and that over time, the mutual gravitational attraction of its matter would slow the expansion rate. 

    From this there were two possibilities:

    1. Gravity would eventually win, the universe would stop expanding and then collapse back in on itself.

    2. The universe didn't have quite enough mass to stop the expansion completely, and it would continue to expand forever.

    The study that opened the whole dark energy can of worms was trying to determine which of these was true.

    What they did was measure the recession velocity of various galaxies at various distances.  Since the further a galaxy is from us the longer it took its light to reach us, you were looking further and further into the past as you looked at more and more distant galaxies.

    You then plot a distance/recession graph.  If the rate of expansion had been constant over time, you would get a straight line. Of course, this was not what they expected to see, they expected to get a curve, the degree of which would indicate how fast the expansion was slowing. 

    They got a curve, but one that curved the opposite direction, indicating that the expansion rate had increased over time.  Something was causing it to speed up.

    They settled on calling it "dark energy" just for the simple fact that the term "dark matter" had already been in usage (And this is the only thing the two have in common).

    As to the exact nature of dark energy, it is still an unsolved mystery.

  4. 2 hours ago, DanMP said:

    You seem to know a lot about DM, so maybe you can tell us more:

    DM particles attracted by massive objects, like stars and planets, may form DM atmospheres around them?

    If not, why not?

    If yes, can we make a distinction between the mass of the planet/star and the mass of its close DM atmosphere, the denser part (assuming that DM density increases towards the planet/star center, as for regular matter atmosphere), in order to account for all the dark matter?

    Since DM does not interact (except gravitational) with regular matter, it is possible that the above mentioned hypothetical DM atmosphere to be not only around the planet/star but also inside it? The estimated 90% includes that DM?

    Genady has a point.    Gravity causes planets,etc. to form because regular matter interacts electromagnetically. Collisions, friction etc. is a result of this electromagnetic interaction.  A secondary result of this interaction is the production of electromagnetic radiation.  The production of this comes at the expense of kinetic energy from the matter involved. Two particles collide, emit some EMR and separate, but at a slower speed than they met at. This happens enough and a clump of matter of matter forms.

    DM does not interact electromagnetically, not only does that mean it doesn't "collide" like regular matter, but it doesn't have the same mechanisim to shed KE.  A DM particle can approach a planet, pass right through it, and fly off with the same speed it started with.  There's is nothing to hold it in the vicinity.

    Having said that, There are ways for DM to clump. Gravitational interactions can cause such distributions.  But compared to electromagnetic interaction, they are very,very, very, weak,  and produce results much slower.  The Universe just hasn't been around long enough for small compact collections of DM to form, Just much, much larger and diffuse collections like galactic halos.

  5. 10 hours ago, hoola said:

    with these estimations, and if the distribution is inconsistent on small scales, does our particular vicinity within the galaxy allow the possibility of a "dark matter weather", in that within small regions, perhaps "clouds"  of DM pass through the earth at various times, and contribute to the small variations in the value of G measurement?

    The first thing to keep in mind is that while 90% of the mass of our galaxy is estimated to be dark matter, This includes the entire DM halo or a spherical volume that extends well beyond the visible matter disk of the galaxy.  Once you spread it's mass throughout that huge volume, you end up with an extremely low density. 

    The other thing is that even though, if you were to take the total mass of the solar system and spread it out evenly throughout a spherical volume enclosed by Neptune's orbit, you would end up with a overall density that would put a man-made vacuum to shame,  it would still be many many times denser on average then, say, a 10 parsec radius sphere in our part of the galaxy. And that 10 parsec sphere would, still contain more regular matter than DM.

    It is estimated that the total mass of DM in the Solar system is equivalent to that of 1 small asteroid. Even a 10 fold increase in this density would be insignificant gravitationally to the Solar system.

    If this is the case, then how is it that DM can cause discrepancies in the rotation curves or galaxies? 

    The visible matter in galaxies like the Milky Way is concentrated in its central bulge and thin disk.  So if you calculate orbits based on visible matter, you need to take this distribution into account.  DM however, is spread out spherically, and the vast majority is "above" and "below" the galactic disk.  And any mass closer to the center of the galaxy than a given star, has a gravitational effect on that star's orbit around the galaxy.

    So, for example, if we take that 1 small asteroid's amount of mass spread out throughout the Solar system, and apply that density to the volume of the sphere contained within the Sun's galactic orbit, you get a total mass of DM that is a significant fraction of the total mass of the visible mass of the Milky way; enough to have a noticeable effect on the Sun's galactic orbit.  

    The upshot is that star systems like the Solar system are "matter rich dense spots", which makes their internal orbital mechanics essentially immune to the  kind of DM density variation likely to occur.

  6. 16 hours ago, Sensei said:

    The seasons are here only temporarily..
    After billions of years, the Earth will face the same problem as the Moon, i.e., a tidal lock towards a heavier space object..

    Assuming the Earth isn't engulfed when the Sun enters its red giant stage, you'd be looking at something more like trillion of years, with a lot happening along the way.

    Right now, the Moon exerts the largest tidal effect on the Earth,  So, first it will lock to it.  Tidal braking from the Sun will continue to work to slow its rotation, But the Moon will fight it. The basic effect will be that as the Sun slows the Earth, it begin begins to rotate slower than the Moon orbits.  In this scenario, the Moon-Earth tidal reaction is for the Moon to give up some of its angular momentum back to the Earth, dropping into a lower, even faster orbit.   Even if, at first, the Sun has the advantage, the Moon will eventually move in close enough to once again be the dominate tidal effect,  The Earth's rotation will begin to speed up again, with the Moon getting closer and closer.

    Then eventually, the Moon would pass below the Roche limit and break up into a ring.  With its mass spread out in evenly around the Earth as a ring, it loses it tidal influence, and now the Sun could eventually lock it to itself.

    And even being tidally locked to the Sun wouldn't guarantee an end to "seasons".  The Earth could be tidal locked to the Sun and still have an axial tilt. It would rotate once per orbit, but the North pole would still lean towards the Sun at one part of the orbit, and away half an orbit later.  We see this with the Moon, which is tidally locked to the Earth, it has a small axial tilt of 6°  It alternates between showing us more of its North pole or South pole during it orbit.

  7. When I was growing up in the '60, living in Northern Mn.,  my dad was driving to work early one morning, passing through a small town, and noticed that he was feeling chilly.  He checked the car heater and it was full on, and since it usually did a good job, he suspected something was wrong with it.  Just then, they announced the temp in the town he was in over the radio.  it was -40 degrees.  He thought, "Ah, that explains it." and continued on into work.  ( He worked in the iron mines, which were open pit mines, which,  during the Winter, sunlight never reached the bottom of, so who knows how cold it was there.)

    On 12/24/2022 at 7:21 PM, StringJunky said:

    The first time I experienced  0f in the late eighties, I remember lifting a metal bin lid and my fingers sticking to it quite rapidly.

    During one recess in grade school, someone stuck their tongue to the outside of a metal door during the dead of a MN winter. (like in "A Christmas Story")

    However, instead of the calling the Fire Dept, and pulling him loose, a teacher simply poured warm water over the area until it heated up enough to free him.


  8. 17 hours ago, tmdarkmatter said:

    I am sorry, but even in the "highly simplified" image of Wikipedia it does not seem that the light passes close to the black hole of the "lens galaxy":


    The only distances that matter are the distances between source, lense, and observer.

    It seem highly improbable that it is the light passing closest to the black hole that we see in the Einstein ring. If you watch the Andromeda galaxie, you can see that the center of the galaxy seems not to be transparent from a distance. Rather this light seems to be passing by the galaxy. If you analyze the sun, it is made of trillions of atoms. The same happens with galaxies, they are made of billions of stars, but work together to create the effect.

    The actual amount of bending of the light path passing by the galaxy is very, very, very tiny.  To see this Einstein ring . we need to be the correct distance from that galaxy in order for the  bent light to converge where we are.   For example, we could use the Sun as a gravitational lens, but to do so, we would need to be 542 AU from the Sun, because light grazing the sun deflects light by just 1.7 seconds of an arc.

    Now consider that the galaxy bending the light is billions of ly away, and keeping in mind that just 1 light year is ~117 times longer than 543 AU. Just how much do you think the light passing the galaxy would need to converge on us?  Magnitudes less than it does passing the Sun.

    Secondly, Astronomers, astrophysicists, etc. are well aware of the Relativistic effects that exist, and how to calculate them.  If they were a significant issue, they would be factoring them in already.

  9. 49 minutes ago, tmdarkmatter said:

    The question is, if time passes by slower close to heavy masses, what effect does that have on light passing by a heavy object (black hole). According to Einstein, all processes take place slower and, although light keeps travelling at the speed of light, we (from our point of view) should see that this light should pass by slower. In the intergalactic space, however, the total opposite should happen. As time goes by faster and the light there also passes by at the speed of light, from our point of view we should see this light travelling faster than the speed of light as we know it. If this is real, the galaxies we see, should actually be slightly farther away from us, because the light was travelling faster than we think, a light year would be a bigger distance in the intergalactic space. And if we watch the center of our milky way, it should be somewhat closer to us, because the light was travelling slower. A light year would be a smaller distance.

    Please tell me what you think.

    This is the difference between "proper" light speed (that measured locally), and the  "coordinate" speed of light,( the speed of light at some distant point, measured by our local units of time and space). 

    So yes, light passing say, by the surface of the Sun, would appear to be moving just a tad slower than c, as measured by us further out (Though someone at the surface would measure it as moving at c).

    How would this effect our measurements of interstellar or intergalactic distances?  Insignificantly.  The very slight difference this might make in any distance measurement is completely overridden by other factors that lower the accuracy of our distance measurements.  In other words we don't claim that our distance measurements are accurate enough in the first place to worry about it. For example, take the star Betelgeuse. It is given a distance of 548 ly with an error of +90 to -49 ly.    This potential error range is magnitudes larger than any  due to a difference between proper and coordinate light speed.


  10. 1 hour ago, MigL said:

    I would not rule out an errant Ukrainian S-300, but it would have to be nearly 180o off course to hit areas of Poland. Russia fired more than 100 missiles, also S-300, yesterday, mostly targetting power generation infrastructure. The S-300 is not very modern to begin with, and as most have been 're-commissioned' with washing machine parts, I don't imagine they are very reliable. I still believe it originated from one of the Russian firing positions, until evidence proves otherwise.

    This might give NATO the excuse needed to establish a 'no-fly' zone over areas of western Ukraine that border NATO countries, so as to prevent further incidents.
    Just as Russia needs to protect itself from those Nazi Ukrainians by invading them, so should NATO be able to protect itself from the Russian 'special operation'

    For the very reason that it gives NATO an reason to increase air presence in the region is why I have my doubts as to this being Russia.  They are having trouble enough with Ukraine, why would they take an action that would only make things worse for them?

  11. 2 hours ago, tmdarkmatter said:

    This correlation would also be clear if it would be between observed redshifts and exposure to gravity multiplied by time of exposure. The farther away a galaxy is, the higher should the exposure to gravity be in total.


    In this regard, it is highly suspicious that the only big galaxy (easy to study) next to us (andromeda) is moving our way and is not moving away. And it is also suspicious that such galaxy movements are also difficult to confirm with all other close galaxies, because obviously their speed away from us should be much lower than the speed of the distant ones.

    The first argument is just a rehash of the old "Tired light" argument which has been dismissed because it is not consistent with observations. 

    As far as Andromeda goes,  No, it is not suspicious at all that Andromeda is approaching, as it is part of our local gravitationally bound group of galaxies.  The gravitational attraction between these galaxies holds them in orbit around their common center of gravity.  Galaxies are not evenly spread out, but are grouped in a hierarchy of structures; groups, clusters, super-clusters, with voids in between.  It isn't until you get to the size range of the larger structures that the overall expansion of the universe overrides gravitational attraction

    If you had done any serious investigation into the subject, you would have learned this, and your lack of knowledge of it shows that you didn't really bother to do more than just scratch the surface of the subject before jumping to conclusions. If you are not going to go to the trouble of doing even a moderate amount of effort of gathering basic information,  why should anyone else go to the trouble of taking your musings seriously?

  12. Some issues with your idea:

    It fails to explain why DM(Dark matter) is concentrated as spherical halos surrounding galaxies. Our own galaxy's DM halo only extends out to 210 thousand parsecs (compared to the 27 thousand parsec diameter of the galaxy itself). It is within this radius that the "extra mass" is needed to explain galaxy rotation curves.  If the majority of light is contributed by other galaxies, then it would not be concentrated in a region around us (or any other galaxy.) But the vast amount of dark matter mass would be evenly spread out through the universe.  Andwith this being the case, it would have no gravitational effect on individual galaxies' rotation. ( Mass evenly distributed throughout the universe has no effect locally, as the combined effects cancel each other out over "small"(compared to the size of the universe) regions.

    Put another way, for things to work the way we see them happening, the extra mass of DM has to be mostly clumped around galaxies, and not spread out evenly through the universe.

    And if that much light was concentrated in the region around galaxies, we would see it.  Even intergalactic space isn't completely empty, and the little material there would scatter enough of that light to produce a visible "glow"

    It fails to explain why we have found some galaxies that seem to show little to no indication of DM. They produce just as much light as other galaxies, and are being bathed in just as much light, but do not behave the same.

    Then there are observations like the Bullet cluster, where we are looking at the aftermath of galactic collisions.  Here we can use gravitational lensing to locate concentrations of mass, and have noted that after the collision, there is a region that shows a concentration of mass that is separate from any visible light source.  This is what one would expect if the DM was separated from its parent galaxy by the collision.  This is not something that could occur if DM was the result of the mass of light.



  13. On 8/12/2022 at 10:38 AM, TheVat said:

    (started writing this before exchemist posted)

    Due to the inverse square law, the gravitational effects of distant stars are negligible.  

    When you were born, a neighbor in a house near the hospital was running their vacuum cleaner.  This created some EMF emissions that might interfere with old tv signals back when they were on VHF frequencies, and would very slightly impact baby you's atoms.  Would that make you a Vacuum Cleaner Baby, destined to go through life being tidy?   Or perhaps there was a garbage truck backing up outside the wall of your birthing room.  Would the miniscule gravitic force of that truck make you a Garbage Baby, destined to pick up debris?  That's about how much sense astrology makes.

    It's not even the inverse square law that's meaningful, but the inverse cube law of tidal effects.

    Take a body like Mars, It has a gravitational pull on you, but it also has one on Earth, and since both you and the center of the Earth are nearly the same distance from Mars(when compared to the distance to Mars),  the acceleration experienced from that pull is almost equal, and it is only the slight difference that could have any effect on you. This is the tidal effect.   These types of tidal forces fall off by the cube of the distance.

    Given the mass of Mars, and it distance at its closest to Earth,  a 0.2 gram mass at a distance of 100 meters would exert a larger tidal force on you than Mars would.

  14. From my limited understanding, the reason "run of the Mill" neutrinos have been excluded from the list of candidates for making up a major component of dark matter is that it would have altered the formation of the universe.  That many neutrinos would have prevented the small scales structures from forming as early as they did.

    That doesn't mean neutrinos are out of the question entirely, there is the hypothesized "sterile" neutrino, which doesn't interact with other matter at all, except gravitationally. Some recent findings have suggested to its actual existence.

  15. On 10/8/2022 at 4:05 PM, Peterkin said:

    He has zero chance of winning Ukraine. And he has an ego the size of the moon, and he's terminally ill. If he can't have what he wants - making the Russian Empire Great Again


    In any terms that matter, he's already lost, and did the moment Ukraine didn't fall within a few days of the start of the attack.  The action ended up having the opposite effect he wanted. It solidified NATO, and actually influenced two nations, previously reluctant to do so, to join.  It exposed the Russian military as being a paper tiger( It has lost its position as being considered the third most powerful military, with other nations now in the running for that honor).  Instead of strengthening the Russian Empire, it has crippled it.

    Even He were to finally prevail in terms of capturing Ukraine on the battlefield, all he will have done is have taken some ground.  The major goals of the invasion have already evaded him.

  16. 22 hours ago, Sensei said:

    People who own laptops often simply push the flip cover down, which hibernates the system, instead of shutting it down. This causes problems in some situations. I know that Windows Media Center (the TV Tuner application) in Windows 7 is buggy and consumes the entire disk until the system is properly shut down and restarted (which obviously kills services). I found a workaround - shut down only the service in the Administration Panel. The files are locked permanently by the service - no cleaning, deleting, etc. can remove them while the service is running. In Win10 WMC was removed, but some other service or app can have similar issues.

    Another thing you should do from time to time is do a "Restart" rather than a "Shut down".   I know it sounds counterintuitive, but Restart does a fresh reboot, While Shut down preserves a number of settings to speed things up upon turning the computer back on.  If one of those processes is what is causing the problem, it will be carried over to when you turn the computer back on.

  17. On 9/27/2022 at 7:13 AM, paulsutton said:

    Looks like the NASA Dart mission test was a success.   A couple of questions from this


    If an asteroid was heading towards the Earth and we used a similar method to the above to change the trajectory is there a danger that this could cause any asteroid to hit the moon ?

    (Similar method, as if this can happen anytime,  even 100 years from now we will have moved on technically but still need to do this. )

    In which case, would we need to consider any impacts on Moon bases

    Is there a danger that any impact on the moon could cause debris from the Moon to hi the Earth, or any satellites in orbit ?

    Is there a danger of moon impact, shifting the orbit of the moon or would any such asteroid need to be a certain size / speed for this to happen

    Thanks for any help, 




    Above is an image showing the relative sizes and distance between Earth and the Moon. Not only is the Moon a significantly smaller target, but there is a huge amount of space that allows for a comfortable miss of the Earth, without even coming close to the Moon.

  18. 4 hours ago, exchemist said:

    China and N Korea are ruled by totalitarian despots like Putin, so the answer is obvious. Vietnam has not sided with Russia but is maintaining a neutral stance.

    The rest of your post is too incoherent to respond to - though a sort of blurred hatred of the West seems to come through. 

    In addition, China's "support" of Russia only goes as far as what China sees as benefiting themselves.  They would not be adverse to "supporting" Russia in an endeavor that would ultimately weaken Russia.

  19. 42 minutes ago, iNow said:

    I mean, what's next? A person who is just a former president and is once again little more than a regular old private citizen gets treated as if... as if... as if he were just a regular private citizen!?! Where will this jackbooted thuggery end?!?

    A lot of Republican leaders are going around ringing the alarm of " If The FBI can do this to Trump, they can do it you!"

    Of course, the the FBI could already have done this to the average citizen. That's not what bother them. It's that if they could do it to Trump, they could do it to them!  They see it as an erosion of the protective shield created by being rich and powerful.  It removes the power behind the words, "Do you know who I am?"


  20. 19 hours ago, kenny1999 said:

    Approximately how long will it take for the earth to spin down to an extent that is going to affect human's life? Is there any estimation?

    Due to the Moon's tidal effect, the Earth's period of rotation increases by about 1 sec every 50,000 yrs. (in 50,000 yrs, it will take the Earth one second longer to complete a rotation.) 

    As to affecting human's lives, It already does, to a certain extent.   We have reached a point where accurate time measurement has become vital to a great number of fields.   Because of that, the need for a standardized unit of time became very important. This is the second.  For a long time, the second was based on the Earth's rotation. That is, until it became apparent that this wasn't a constant.  The second was switched to be based on something known to be constant, and fixed on that value. The Earth's rotation still changed over time.  

    Sure, it was only by microseconds a day per year.  But the effect was accumulative.  For example, imagine a clock that runs slow by one second per day. after 1 day, it will be late by 1 second, after two days 2 sec,... after 60 days, its behind by a full minute, etc.

    The same thing happens with the Earth,  from the time we set the length of the sec to a fixed value and now, our Clocks(based on that sec) and the rotation of the Earth vary slightly  Just a tiny bit each day, but it adds up over time.  So, in order to keep them our clocks from drifting too much from the position of the Sun in the sky, every so often a "leap second" is added to our time keeping systems, to line them back up again. (kind of like resetting that clock that runs slow from time to time).

  21. Even interplanetary space isn't completely empty.  So technically, there would be some small amount of friction. But things aren't that simple. There are all kinds of things that effect the Earth's rotation.  Tidal interaction with the Moon is a major one. This transfers angular momentum from the Earth to the Moon's orbit, slowing the Earth's rotation over time (on average*)  If were to remove the Moon from the equation, Tidal interaction with the Sun would slowly decrease the Earth's rotation until it locked to the Sun keeping one face to it at all times( unless, due to some effect, it settled into some other orbital-rotation resonance like Mercury has).  But even that wouldn't stop the rotation rate from changing.  The Sun is losing mass as it ages, so the Earth would move to a higher, slower orbit in response, with the rotation slowing to keep pace...   When all is said and done, it is a complicated dance.



    * other things like major shifts/earthquakes can cause the Earth to speed up its spin.  If it causes a net shift inward of the Earth's mass, it is akin to an ice skater bringing in her arms (Only to a much, much smaller degree). Collisions with medium to large meteorites can add or take away spin

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