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Janus

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Posts posted by Janus

  1. 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

    https://www.nasa.gov/planetarydefense/dart/dart-news

    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, 

    Paul

     

    earthmoon.jpg.57fafcee3bb67c45008473b9ce145589.jpg

    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.

  2. 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.

  3. 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?"

     

  4. 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).

  5. 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

  6. We could find out as early as today what exactly was in the warrant. That is, unless Trump objects to it being unsealed. And even that may only delay things. He could object, the Judge issues a stay to give his attorneys time to present their arguments, and then he'd rule on that objection.  He could very well overrule Trump's objections. (For example, if Trump tried to argue privacy issues, the judge could rule that it's too late for that since he is the one that made the warrant public knowledge in the first place.)

     All these Republicans were howling about "Show us what was in the warrant!",  And Garland's response was, "Well Trump has copies, and he is free to make them public if he wishes.  We were just trying to respect his rights. But, if that's what you really want, okay."    But that's not what they really wanted. They just wanted to howl about the warrant not being unsealed. 

    In addition, If Trump objects, and his objection is upheld, then it will be Trump keeping it secret, not the DOJ. (Garland did the legal equivalent of "I am rubber, and you are glue...")

  7. 1 hour ago, TheVat said:

    Trump wrote. “Nothing like this has ever happened to a President of the United States before.”

    Trump still hasn't gotten it into his head that he is no longer POTUS. He is an ex-POTUS. 

    And while it is true that nothing like this has happened to an ex-POTUS either, neither has there ever been an ex-POTUS who warranted such, until now. * 

    It is telling that when the news of the search by warrant broke, the big question of "What are they looking for?"  came not from surprise that he was suspected of a crime, but from not knowing which of the many crimes he is suspected of they were looking for evidence of.

     

    *Even Nixon had the sense to resign and broker a pardon by promising to ride off quietly into the political sunset.

  8. On 7/31/2022 at 6:34 AM, exchemist said:

    You can read about it here: https://bletchleypark.org.uk/our-story/bletchley-park-and-d-day/

    Though what this has to do with moon landings, or secrets kept by the state. I don't know - unless you mean the Enigma-coded  messages sent by the German military.   

     

    If the US had such an ability, capable of fooling not only the experts of the time, but for decades afterwards, as early as the 1960's, It wouldn't have taken so long for the USSR to fall.  Heck, they'd be ruling the World by now.  This is such a conspiracy theory trope: Claim that the conspirators have the capability of pulling off the near impossible, but they only used it for something relatively trivial. 

  9. On 7/26/2022 at 11:22 PM, Joshcitylife said:

    r perhaps the more insidious reasoning for this exploration to the moon was because of the tension between two powerhouse nations during the Cold War. 
     

    This tension is likely the strongest evidence against the Moon landings being faked.   The Cold War was, for the most part, fought in the court of world opinion; each side trying to convince other nations that their system was the better of the two.    And yes, getting to the Moon first would have been a huge feather in the cap of the country that did it, and was the major motivation behind the program.

    And while you might think that this would lead to the temptation to "fake it",  Neither side would have risked trying that.   The blow to international prestige caused by being caught would have been magnitudes worse than the gain from getting away with it.  And both sides knew that the other would have experts pouring over every frame of footage shot, every photo shot, etc. looking for the evidence they needed to expose fakery. 

    So, the side that was trying to fake it would have had their own team painstakingly go through everything, looking for anything that would give up the game before any of it was released. So things like flags "waving" when they shouldn't be wouldn't have made the cut unless there was a explanation for it that was consistent with it being on the surface of the Moon in a vacuum*  The idea that they would miss all these things that some people point to as "proof" of the landings being faked borders on the insane.  This is not some Hollywood production where they'll let things slide because they understand that the majority of the audience won't notice or care.

    Before the US would have even considered faking it, they would have gathered experts and asked them if it were possible to fake it. And the answer would have been "No. Not the the degree that would fool our counterparts in the USSR."

    I'll give you an example of what I mean. Recently, I saw a video of a group of CGI experts reviewing some footage of a robotics demonstration. A fair number of people were out there claiming that this footage had been faked with CGI.  Their conclusion was that it was real footage.  Mainly based on the fact that there were things in the footage that just couldn't have been done CGI without leaving clues that they would have spotted.  They knew what could be done CGI, and what couldn't.

    So the idea that the US could have faked it well enough to fool the USSR, or that USSR could have exposed them and didn't, is laughable.

    The very fact that USSR never made any attempt to claim the US landings were faked is because it would have made them a laughing stock in the court of world opinion.

    * And it wouldn't have been good enough to offer some "hand-wavy" explanation.  As stated above, the USSR's experts would have gone over with that footage frame by frame, comparing the flag's motion against what would be expected for it being in a vacuum on the Moon vs. being disturbed by moving air.

  10. Nothing can escape the event horizon of a black hole, not even light.    Mass and energy both contribute to gravity.  So its not as if "mass breaking down into energy" would decrease the gravitational field of the black hole or cause its event horizon to cease to exist.

  11. On 7/3/2022 at 5:22 AM, Steve de Jonge said:

    Now download a photograph of the full Moon, have a good look at it, and ask yourself - is that how a hemisphere, in a vacuum, reflects light from a single source? Consider the light (from directly behind the photographer) striking the Moon's edges; what should be little more than a glancing blow (if starlight was inclined to race aimlessly into space) actually results in a 180 degree reversal of its course,

    It is a matter of specular vs. diffuse reflection.  Specular reflection is mirror-like, where the incidence angle and reflection angle are the same.  With diffuse reflection, the reflected light scatters in all directions. Which domimates in any given scenario depend on the nature of the reflecting surface.  A mirror is highly specular, while a sheet of paper is highly diffuse. 

    The Moon falls on the paper end of the spectrum.

    Here is an image of three spheres lit by the same light source, but with different specular/diffuse ratios:

    lighting.png.75cb1cdac999ca743a729c22c209268e.png

    On the bottom left is what you'd see from a mirror-like surface of pure specular reflection;  one small bright dot of light.

    In the top middle we have a mix of specular and diffuse reflection. You get a bright highlight in the center and things darken as you move to the edge.

    Then on the bottom right we get a fully diffuse sphere, Which looks evenly lit all around. (the slight darkening at the upper left is caused by the sphere not being perfectly centered in the frame, so the camera sees slightly around to the unlit side.)

    The last one is what most closely matches the Moon in the sky.  In addition, the surface of the Moon is not smooth, and this just adds to the diffuse refection overall.

    You seem to expect the Moon would behave like the mirrored ball in the lower left.  Given the fact that the Moon doesn't have a mirror-like surface, this simply would be possible.

    And even if the surface was purely specular in nature, the fact that the surface is bumpy and irregular would have it looking something like this:

    lighting1.png.c14596cc637083d9afe8319fa7a4dada.png

    and not the single point of light.

  12. On 6/29/2022 at 12:39 PM, swansont said:

    They had already appeared before the committee. It’s doubtful they would have let her testify if it wasn’t corroborated.

    The republican responses have not been under oath, and sometimes, like this, unattributed. Take them with a huge grain of salt. Pay attention only if they, too, testify under penalty of perjury  

    Adding to the mix, apparently there are sources in the Secret Service that have said they had also heard the story about Trump's behavior in the SUV.    Did the story possibly grow in the retelling? It happens.  But again, Hutchinson was clear that she was only repeating what she was told.  The fact that others say they heard the same, at the very least, seems to confirm that the story was floating around.

  13. 11 hours ago, MPMin said:

    Thanks Janus for your detailed reply.

    It’s just occurred to me that defining the synchronisation of the clocks it’s self is a conundrum to me. 
     

    I can imagine that if all clocks were in the same proximity that they could all be synchronised together. Let’s assume we synchronise all clocks while they are together and then before the experiment starts, we move clock B and observer B 1 light minute away while leaving Clock A and Clock C begins with their respective observers. Would clock B still be synchronised with clocks A and C after it reaches its position 1 light minute away and does it matter how long it took for clock B to reach its position as to how much the synchronisation changed if at all.

    Let’s assume that clock and observer C are due to depart clock A at 10:00:00am in A’s frame of reference. I’m going to take another stab in the dark and assume that if the clocks were all synchronised (without taking into account the effect of moving clock B into position had on the original synchronisation) as observer B is 1 light minute away from clock A, when observer B sees clock A strike 10:00:00, clock B will be seen as displaying 10:01:00 by observer B in his own frame of reference. 
     

    If clock A and C show the same time when Clock C departs at 10:00:00am in A and C’s frame of reference, 

    When C is half a light minute away, does that mean that from A’s frame of reference that C is half way through its trip to B? Does it mean that from C’s frame of reference, it has already arrived at B? If getting any of this, that should mean that when C arrives at B that, observers C and B will see clock C as being 10:00:30 while Clock B will be 10:01:30 and observers C and B will see that clock A is 10:00:30 from C and B’s frame of reference. Observer A from A’s frame of reference will see that clock C as showing 10:00:15 while seeing clock B to be showing 10:00:30? 

    Suspect I’ve got it all wrong though. 
     

     

     

     

     

     

    The synchronization of clocks in SR can be the most difficult concept to grasp when you first start learning the subject. This is mainly because most people come into the subject with preconceived notions about time that they have to lose in order to go forward.

    That being said, there are a couple of points we need to go over.

    Frames of reference:  You are treating them as being the same as "point of view", such as "A's frame of reference, and "B's frame of reference". This is not what frame of reference means in Relativity.  It is just a choice of coordinate systems. Any object simultaneously exists within an infinite number of frames of reference.  Which one we use when dealing with the object depends on what is most convenient for our purposes at the time. 

     In SR, we deal with inertial frames of reference. Put simply, these are reference frames with constant motions with respect to each other. Again, any object exists simultaneously within an infinite number of these, but it is, in many cases, easiest to work with the one that the object itself is at rest with respect to.  This can be referred to as the "rest frame" of the Object.  And while it will sometimes be called, for example, the "reference frame of A", this is really just shorthand for "the inertial reference frame that A is at rest with respect to".

    So let's look at A, B, and C.  At the start of this exercise, they are all at rest with respect with each other, and thus all at rest with respect to the same reference frame. In other words, at this point, there is only one reference frame we need to consider.

    Once C begins its trip, A and B remain at rest with respect to the same frame as before, but C is in motion with respect to this frame. C is however at rest with respect to another inertial reference frame, one moving at 0.5c relative to the frame A and B are at rest with respect to.  It has "changed rest frames"  So now we have 2 inertial frames from which we can consider things.

    Now, when it comes to synchronizing clocks:  As long as the clocks are at rest with respect to the same reference frame, there is no issue in synchronizing them, no matter how far apart they are.*  If you "see" a clock 1 light min away as lagging behind yours by 1 min.  You know that that the light carrying this info to you left 1 min ago, when your clock read that time.  In other words, 1 min ago both clocks read the same, and as long as nothing has changed for either clock since, they read the same now. This is true for anybody at rest with respect to this frame, no matter where they are located.

    However, things change if you consider the clocks from a reference frame in motion with respect to these clocks.

    For example, consider the rest frame of C, the instant it starts moving from A to B, It sees clock A read 0, and since there is zero distance between it and A, it knows that Clock A reads 0 at  that moment. It sees clock B reading -30 sec, It does not however conclude that Clock B reads 0 at that moment, but would conclude that it read +15 sec.  In other words, C would conclude that clocks A and B are out of sync by 15 sec, and this 15 sec difference remains throughout the trip.  The upshot, is that while both A and B conclude that their clocks read 15 sec "at the same time", C concludes that A reading 15 sec and B reading 15 sec, occurs at different moments in time.  A and B's "at the same time" is not the same as C's.

    So when you ask "When C is half a light minute away, does that mean that from A’s frame of reference that C is half way through its trip to B? Does it mean that from C’s frame of reference, it has already arrived at B?"

    You have to be really specific as to what you mean.  When A determines that C is halfway to B, this is when clock A reads 30 sec.  According to A, C's clock will read 0.433 min.  C will say that it is halfway to B when it's clock reads 0.443.  There is no disagreement here.

    However, according to C, A does not read 30 sec until C's clock reads 0.577 min. (after he passes the halfway point, but before he arrives at B)

    Again we are dealing with the fact that A and B do not always agree as to what occurs "at the same time" . For A, his clock reading 0.5 min, and B's reading 0.433 min occurs at the same time, and for C, A's clock reading 0.5 min and his reading 0.577 min occurs at the same time.

    If you mean when A "sees" C arrive at the midpoint, this occurs when A's clock reads 45 sec, at which time, according to A, C is 3/4 of the way to B.

    It is really important not to mix up what one "sees", with what one would determine is happening at that moment.  Most times in dealing with Relativity, we don't worry about what is "seen" and instead focus on what is determined.  Put another way, we "cut to the chase" of Relativistic effects without worrying about light propagation delay.

    An example of the difference:

    For this example, we will assume that C has been already traveling at 0.5c relative to A and B prior to passing A(This avoids complications caused by instantaneous velociyy changes.)

    As C passes A, they both "see" Clock B reading 30 sec earlier than Clock A.

    Observer A, knowing that A and B have been at rest with respect to each other and 30 light sec apart, concludes that this light left 30 sec ago, and That clock B has ticked off 30 sec since then, and, at that moment reads the same as his own.

    But what does C conclude?   We already mentioned that due to length contraction, he would say that B is, at that moment 0.433 light min from A( and himself).  But, the light he is now seeing from B left B before C reached A, and when the distance between himself and B was greater.  Since one of the precepts of SR is that every inertial frame measures light as traveling at c with respect itself, C must assume that the light he sees coming from B as he passes A, left B when they were 0.866 light min(~52 light sec) apart, and it took 52 sec for the light to reach him.   52 sec have ticked off since the light left B and C sees it. This is more than the 30 sec difference that he sees between A and B's clock.  So, as he passes A, he must conclude that the Clock at B already reads sometime later than the clock at A*

    So here we have two observers, at the same place, seeing the same thing, but making different(But equally valid) conclusions as to the state of a distant clock at that time.

    * Due to time dilation, C would also conclude that Clock B ticks 0.866 as fast as his own, so in his 0.886 min, clock B ticks off 0.75 min or 45 sec.  45-30 = 15, which is the 15 sec difference I mentioned earlier.

     

     

     

     

     

  14. 6 hours ago, MPMin said:

    Thanks again for your reply.

    I’m just going to reiterate what you are saying in my layman’s terms to confirm my understanding. If I’m getting it wrong please correct me.

    Using the previous scenario where all clocks are synchronised before C departs from A, lets assume C departs from A at 50% speed of light and lets assume acceleration happens instantaneously (just to skip the effects of the acceleration phase and to only consider the constant speed phase). Let’s assume that from A’s frame of reference, C takes 1 min to travel from A to B travelling at 50% speed of light. Let’s also assume all clocks are always within their respective observers frame of reference and to be clear the scenario only describes what each observer sees as per the light that enters the eye.

    As soon as C departs A at 50% speed of light, from A’s frame of reference, A sees clock C ticking 50% slower than his own clock at A and observer C from his own frame of reference sees clock A ticking 50% slower than his own clock at C.

    Observer C from his own frame of reference never notices any change to the rate of ticking of his own clock. 

    From the moment that  C departs A, observer C from his own frame of reference sees clock B ticking 50% faster because C is encountering more light pulses from B as C moves towards B

    I’m going to use my intuition to make these next assumptions but i would imagine that, as soon as C left A at 50% speed of light, B would see that C was still stationary at A until C had reached the half way point in terms of distance between A and B. As C passes the half way point, observer A would see that 30 seconds had elapsed on his own clock at A but only 15 seconds had elapsed on clock C. 

    I’m still assuming that, At the half way point observer C sees that only 15 seconds has elapsed on his own clock and only 7.5 seconds has elapsed on clock A from C’s frame of reference.

    As C passes the half way point, observer B sees C just leaving A, even though C left A 30 seconds ago from A’s frame of reference and 15 seconds ago from C’s frame of reference. Observer C has also seen clock B ticking faster for the past 15 seconds from his own frame of reference. 

    When C arrives at B 60 seconds would have elapsed for observer A from their own frame of reference, 30 seconds would have elapsed for observer C from their own from of reference and 30 seconds would have elapsed for observer B at their own frame of reference. 

    When i start thinking about what each observer would have seen the times to have been at each stage I can’t resolve the time differences.

     

    First off: if C is moving at 0.5c, No one would see anyone's else's clocks ticking a a rate of 50% slower or faster than their own. The correct rates are ~57.74% and  ~173.2%. This is the result of accounting for both Doppler shift and time dilation effects.  The combination of these gives what is known as "Relativistic Doppler effect"

    What A sees:  C departs at 0.5c, and C's clock is seen as ticking at 57.74% the rate of his own.  It takes C 1 min to reach B. However, since B is 1/2 light min away, it will take A another 1/2 min before he sees this occur.

    Thus he sees C's clock recede for 1.5min, while ticking at a rate of 57.74%, and accumulate 0.866 min.  Since the clock at B will be seen, due to propagation delay, to lag behind his by 30 sec during the whole of this interval,  He will see clock B start at -30 sec when C leaves and 1 min upon C arrival.

    What B sees:  30 secs after C leaves A, he sees leave A.  Since C will have crossed half the distance by then, it will only take another 30 sec for C to arrive.  During that thirty seconds, he will see clock C tick at a rate 173.2% of his own, and accumulate 0.866 min. (1.732*0.5 = 0.866). His own clock will read 1 min upon arrival of C.

    What C sees.  When he leaves A, he sees clock B lagging 30 sec behind clock A, just like A does at this moment  He will see clock B ticking at a rate of 173.2% his own.  By his clock, he will arrive at B 0.866 min later*  and see clock B tick off 0.866 * 1.732 = 1.5 min.  But since he started off seeing clock B reading -30 sec, he sees it as reading 1 min on arrival.

     

    *  Why does C say it only takes him 0.866 min to cross 1/2 light min of distance at 0.5c?  Because for him, the distance between A and B is not 1/2 light min, but 0.433 light min.   This is due to length contraction. Since A and B are moving relative to him, he would measure the distance between them as length contracted.   This brings up something that occurs often when people start learning Relativity.  They try and isolate a single effect, such as time dilation, and examine a scenario using only it.  But you need to take all the effects into account to do a proper analysis of it.

  15. From your image:

    Depth of the hole would be the difference in gravitational potential.  The " steepness" at any point is local gravitational strength.

    So, from this diagram, local gravity would be zero both inside and outside of the "hole".  The walls (if straight up and down) would represent infinite gravitational strength over zero distance.  (Not a realistic scenario) The edges between the walls and the flat areas would have an infinite tidal force.

    Since gravitational time dilation is related to difference in gravitational potential and not a difference in gravitational strength,  Time would run slower at the "floor" of the hole by an amount determined by by the depth of the hole.

  16. 30 minutes ago, WAMF said:

    No I'm saying Dark matter may be a weak magnetic field that permeates all of space. Photons are not produced. All the matter minus the DM and DE is the baryonic matter, that abides by Classical physics . I'm treating the DM and DE as a separate much older system. 

    Light, infrared, x-ray produced by the baryonic matter can travel through the magnetic field, older system unimpeded. Making it invisible to us.

     

    That idea fails on many levels.  For one, for diamagnetism to exert a "force", there has to a variation in field strength. Diamagnetic materials will tend to move towards the weaker part of the field.  So for it to even work to explain dark matter, you would need the field strength to be greater outside of the galaxy than inside it.  So the field would need to have low strength "pockets", one for every galaxy.    In addition, magnetic fields have an orientation, and for this to have any chance of working right, would have to be oriented properly for each individual galaxy.  But galaxies are not all oriented the same, so the field would have to have different orientations at different points.

    This runs contrary to how magnetic fields behave.  So your idea involves invoking a "magnetic field" that behaves nothing like a magnetic field would.

  17. Finnish: kuusi palaa

    could translate to any of the following:

    The spruce is burning
    The spruce returns
    The number six is burning
    The number six returns
    Six of them are burning
    Six of them return
    Your moon is burning
    Your moon returns
    Six pieces

  18. 11 hours ago, Hello2 said:

    I’m having questions with this:

     

    Is it so that the further the galaxie, the larger the redshift?       

     

    And: Are there galaxies with a constant redshift, or is it so that all galaxies with a redshift have a redshift that is increasing?

     

    Further objects only have a larger red-shift due to the fact that the universe is expanding.  If the universe did not expand, there would not be any change in red-shift with distance.

    The amount that the red-shift of any particular galaxy will have changed over the period we have been measuring them is too small to notice.

    But that doesn't mean that we can't measure how fast the universe was expanding in the past.  When we look at the light from a galaxy, that light tells us the state of that galaxy when the light we see now left it.  The further the galaxy is away from us, the longer it takes the light to reach us.  Thus, as we look at galaxies further and further away, we are seeing them as they were when the universe was younger and younger than it is now.  That includes how fast they were receding from us, and the red-shift that the recession produces.

    If the rate of expansion had been constant over time, you would see a one to one relationship between distance and red-shift measurements of recession speed.  If you measure anything else, that means that the rate of expansion has changed over time. It is that simple.

  19. 18 hours ago, Jalopy said:

    I discovered on google that the speed of light and the speed of gravity are the same.

    Does that mean that gravity fails to have any effect on light, because gravity and light travel at the same speed?

    i.e is that why light has no mass?

     

    What are the same are the speed of light (in a vacuum) and the speed of gravity waves.  Gravity waves are not gravity itself, but more like ripples traveling through the gravitational field. Put another way, you can't have gravitational waves without there already being a gravitational field, but you can have a gravitational field without gravitational waves.

    Light interacts with the gravitational field, which is "already there"

    As already mentioned, light has no "rest mass".  However, it still can interact gravitationally.  While in Newtonian physics you need mass to do so, under our more recent understanding of gravity(General Relativity), mass is just one factor that can contribute to gravity. Energy is another, and light does have energy.

  20. 4 hours ago, TheVat said:

    I have two grandparents born in Scandinavia, but am not sufficiently fond of cold (live in South Dakota, so it's nothing new to me, either),  20 hour nights, or those countries.   In a civil war here, I would probably just hunker down.  (what's a bit ironic is that one of my relatives was a polar explorer)

    So I assume either Norway or Sweden or possibly Denmark? (Finland is not actually a part of Scandinavia). My paternal grandfather was born about 100 miles south of the Arctic circle, and  some ancestors from further North.

  21. 2 hours ago, MigL said:

    kind of cold in Finland.
    You might as well move to Canada.

    Ah, but here's the beauty of it: Everyone will be wanting to go to Canada, but only 0.2% of the US population has any claim to Finnish ancestry at all.  Having 4 Finland-born grandparents should put me at the front of the line!

    (Besides, I was born and raised in Northern Mn, cold is nothing new to me.)

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