Did Richards Really Do Away with Einstein?

I'm sorry if this is a stupid question, but I thought that clocks would move slower on Mt. Everest than at sea level because points farther from the center of the earth travel with greater velocity than points closer. What am I missing? Thanks.

I'm sorry if this is a stupid question, but I thought that clocks would move slower on Mt. Everest than at sea level because points farther from the center of the earth travel with greater velocity than points closer. What am I missing? Thanks.

— phaedrus

If Big Bang cosmology is broadly true, then right now, everywhere in the universe, it's the same time since the big bang. (There are complexities having to do with the inhomogeneity of the universe here, but let that pass for now.) It's not like it's 13.7 billion years old around here, but only 2 billion years old in some other galaxy. Of course we can't look and see what time it is in the Andromeda galaxy, since it's a couple of million light years away. But that's simply a limit on what we can observe directly. It's still at least roughly the same cosmic time there. So Einstein didn't do away with a universal time, even if he and his interpreters often say that he did.

You are missing the dilatation caused by the curvature of space-time, i.e. gravitation. Gravitation is weaker on Mt.Everest compared to the sea level.

Although unfortunately Matt Young has inadvertently misled Vic Stenger regarding the quotation from Richards, this in no way makes Richards's "rebuttal" of Einstein anywhere close to being correct. Stenger's explanation in itself is correct, even if not directly addressing Richards's error. As to what Richards has actually written, is just gobbledygook making no sense whatsoever. It hardly can be replied to in a meaningful manner because it is so far from anything scientifically reasonable that there is simply no common ground for a meaningful discussion of that matter between qualified physicists and Richards.

Regarding the time intervals becoming zero in a frame of reference attached to photons (this notion was suggested by Schroeder) such a notion is meaningless because photons, unlike any entities possessing rest mass, cannot be attached to any frame of reference. If they were, they would have zero speed in such a frame, but it is imposssible because all photons always move with the same speed (in vacuum) in all frames of reference (the speed of light). This notion is in fact the seminal concept of special relativity - all the rest of that theory is derived from it.
PS. I've taught all parts of physics, both on undergraduate and graduate levels, for more than half a century.

In reply to Professor Perakh: In fact I sent Professor Stenger the correct paragraph by Mr. Richards, along with the paragraph by Mr. Matzke. I cut out that paragraph when I prepared the essay for PT. Professor Stenger's response seems to me to be still pertinent inasmuch as he shows that there is no absolute time. My own comments are also pertinent, except that I should not have accused Mr. Richards of admitting a weak knowledge of relativity; he did not admit that.

Right now, my wife is doing something at home. She's doing it right now even though I don't know what it is she's doing.

If a clock is moving faster at the top of Mt. Everest than at the bottom, then wouldn't the top eventually be (a) day(s) ahead of the bottom? Which, of course, means that the top would count more sunrises and sunsets and the sun would pass overhead more times. But, how can this be when they are affixed to the same point on the Earth?

While the resident cognoscenti are fielding questions, would you mind clearing something up for me? I understand that the usual figure for the speed of light is its speed in a vacuum, which implies that it moves more slowly through other media. But if that's the case, then how could the speed of light be constant in vacuum? In other words, if light travels at c through a vacuum, then enters an atmosphere and slows down as a result, it would have to accelerate once it re-entered vacuum. The alternative would be that light doesn't slow down as it passes through a medium, which seems to make the "speed of light in a vacuum" disclaimer superfluous.

Obviously, I'm missing something. Would someone mind filling me in?

AT, you are aware that elapsed time (as measured by a clock) and sidreal time (as measured by days) are entirely different? Or was that remark a joke?

So he's not at home and he knows that his wife is doing something (and he doesn't seem to like it), though he doesn't know exactly the situation. How does he know it?

— Koly

While the resident cognoscenti are fielding questions, would you mind clearing something up for me? I understand that the usual figure for the speed of light is its speed in a vacuum, which implies that it moves more slowly through other media. But if that's the case, then how could the speed of light be constant in vacuum? In other words, if light travels at c through a vacuum, then enters an atmosphere and slows down as a result, it would have to accelerate once it re-entered vacuum. The alternative would be that light doesn't slow down as it passes through a medium, which seems to make the "speed of light in a vacuum" disclaimer superfluous. Obviously, I'm missing something. Would someone mind filling me in?

Absolute Time -

I think I can answer that. As I understand from Dr. Pratchett's research, darkness is much faster than light. (That is why a room with no light source is always dark when you first open the door - all the darkness rushes in ahead of the light.) Because mass increases with speed, darkness is also much heavier than light. As more and more days accrue on mountaintops, the darkness flows downwards, eventually accreting on the ocean floor - this is why the ocean's depths are always dark. The excess light is less dense, and is eventually reflected away by clouds - this is why the tops of clouds, even thunderheads, are always light (except at night, when the falling darkness occludes the light).

Therefore, while extra days and nights are in fact accruing on mountaintops, we never notice it, because the light levels even themselves out. Calendar discrepancies are largely ignored, because no one important lives on mountaintops, except perhaps hermits, who don't use calendars in any event.

Rilke's GD -

Yes, that's as helpful as it is interesting. Thank you very much.

AT, you are aware that elapsed time (as measured by a clock) and sidreal time (as measured by days) are entirely different?

Colin, you worry me... %:->

In other words, if light travels at c through a vacuum, then enters an atmosphere and slows down as a result, it would have to accelerate once it re-entered vacuum. The alternative would be that light doesn't slow down as it passes through a medium, which seems to make the "speed of light in a vacuum" disclaimer superfluous.

— Colin

I am so slow, beaten by RGd...

AT - we'll take the sunrise as a basic measuring point. Now, the interval between sunrises is based purely on the speed of rotation of the earth. The intervals measured by a clock are not connected to this rotation. For example, a clock which measures time in terms of seconds, uses as the duration of a second 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at zero kelvins - according to wikipedia.
The point is that these two things are unconnected - the speed of rotation of the earth could change and the number of seconds measured by the clock in that day would shorten.

Now what happens in a GR situation is that the 'seconds' measured by a clock at sea-level and a clock on Everest would have different lengths. So the apparent interval in seconds between sunrises would be different depending on what clock you used, but both the sea-level and the Everest clock would experience sunrise at the same 'moment.

One seldom mentioned consequence of special relativity: as you heat a gas, it becomes heavier because of the greater velocity of the molecules that make it up. To get a measurable effect, you have to have a heck of hot gas because the molecules need to reach near-relatavistic speeds to get appreciably more massy.

Followup question - would light travelling through a medium lose energy, then? Photons exciting electrons into emitting another photon can't (as far as I know) be a free transaction; what is the effect of the energy loss? Does the light move down in the spectrum, or simply become dimmer?

Thanks, by the way, for the answers. Such an interesting thread, bereft of the usual invective.

Could you please elaborate? No, it's no joke. Perfectly valid question.

— Absolute Time

Damn...

Ok, let's race for the Colin's follow up!

Now what happens in a GR situation is that the 'seconds' measured by a clock at sea-level and a clock on Everest would have different lengths. So the apparent interval in seconds between sunrises would be different depending on what clock you used, but both the sea-level and the Everest clock would experience sunrise at the same 'moment.

Followup question - would light travelling through a medium lose energy, then? Photons exciting electrons into emitting another photon can't (as far as I know) be a free transaction; what is the effect of the energy loss? Does the light move down in the spectrum, or simply become dimmer?

— Colin

Followup question - would light travelling through a medium lose energy, then? Photons exciting electrons into emitting another photon can't (as far as I know) be a free transaction; what is the effect of the energy loss? Does the light move down in the spectrum, or simply become dimmer?

— Colin

Well, whatever... Just hope I am not completely useless here...

Remember, time always seems to pass at the "normal" rate for you, in your frame of reference. External events (like sunrise/sunset) might measure as taking less or more time depending on where you are in the gravity field, but there is no "absolute" amount of time the event takes... it all depends on where you're observing it from. Yikes! (grin)

So, then what you are saying is that the clock on top of Mt. Everest is running faster, but time isn't.

— Absolute Time

Um, isn't it obvious? The designer told him.

— GCT

"So, then what you are saying is that the clock on top of Mt. Everest is running faster, but time isn't. If it were time that was running faster, then events (i.e. sunrises, sunsets) would keep in synch with the faster running clock."

AT, there's not a short way to explain what's wrong with this without you learning the mathematics of (at least Special) Relativity. But the upshot is that, if you insist on absolute time and say that only clock speeds vary based on changes in reference frame, then you have separate general laws of physics that apply to different frames. Sizes, masses, and electrical charges of real objects will be different depending on which frame they are measured in. Relativistic spacetime provides a single, consistent model that works anywhere in the universe ...

For example, a clock which measures time in terms of seconds, uses as the duration of a second 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at zero kelvins

you measure that the time between two sunsets is 24 hours. Then compare your results with those in different frames, e.g. your buddy on Mt.Everest measured for the same two events 40 hours

Well imagine my example - a 40 hour day on Mt.Everest would mean your buddy would be very old after 40-50 years (defined as a 365 sunsets, for example). You could watch him age and die, while you would still be only "in the best age". Is his time running faster or not?

Well imagine my example - a 40 hour day on Mt.Everest would mean your buddy would be very old after 40-50 years (defined as a 365 sunsets, for example). You could watch him age and die, while you would still be only "in the best age". Is his time running faster or not?

Then the buddy has a clock which is running faster, but his time isn't.

Then the buddy has a clock which is running faster, but his time isn't.

Well imagine my example - a 40 hour day on Mt.Everest would mean your buddy would be very old after 40-50 years (defined as a 365 sunsets, for example). You could watch him age and die, while you would still be only "in the best age". Is his time running faster or not?

In Gene Wolfe's book "The Sword of the Lictor" Severian goes to a house where the epoch is different, and more distant, as he ascends to higher floors. Evidently the top floor is some millions of years older than the bottom floor. Clearly, this house has been sitting there a very long time, while the different time rates accumulate.

What mechanism would you propose to measure this "time" if not a clock? And by "clock" I mean anything from a pocket watch to a cesium atom.

Comment #23583 Posted by Absolute Time on April 6, 2005 03:00 PM (e) (s) So, then what you are saying is that the clock on top of Mt. Everest is running faster, but time isn't. If it were time that was running faster, then events (i.e. sunrises, sunsets) would keep in synch with the faster running clock.

Can I just say that this is science at its finest. I mean it. I loved this. Not only did I learn plenty, but it was a thoughtful, concise, information-packed, convivial thread. Thanks to all!

I assume that you believe that both persons have witnessed the same number of sunsets and sunrises, then the buddy's watch is running faster but time is running at the same speed for both.

— Absolute Time

Re "So, then what you are saying is that the clock on top of Mt. Everest is running faster, but time isn't."

That's my understanding of it, too. Another way of looking at it would be to say that a strong gravity field causes physical processes to take longer (not just clocks). My way of explaining that to myself is to figure that in stronger gravity (or at really high speeds), photons take longer to get from one atom to the next, and the physical processes with which we deal pretty much depend on those exchanges of photons. Ergo, stuff takes longer in those situations.

Henry

Steve, knowledge has no bearing on truth - this can be empirically proven. Knowledge, of course, is power, which is also energy. And Einstein showed that energy is matter, which has mass. This demonstrates two things - that increasing knowledge increases the knower's mass, and that knowledge is a concrete, physical thing. (It also demonstrates, according to the classic proof, that libraries are dangerous places, due to the enormous weight of accumulated knowledge, but that is neither here nor there.)

Truth, on the other hand, is beauty. And beauty, being an abstract concept, is both unburdened by mass and an essentially subjective quality. After all, beauty, and therefore Truth, is in the eye of the beholder.

Increasing knowledge increases mass, but does not increase the unrelated value of Truth. The addition of mass does weigh down the knowledgable observer, however, who also experiences a faster flow of time and thus aging due to the increased time-space dilation of his own gravitational field.

This is why knowledgable men and women seem more mature, and often feel old, weighed down, and tired when confronted with those who are burdened only by their own subjective Truth.

The clock is running faster. Time is running faster.

Absolute Time: Then the buddy has a clock which is running faster, but his time isn't. What mechanism would you propose to measure this "time" if not a clock? And by "clock" I mean anything from a pocket watch to a cesium atom. ---Chris (first post here for me, hi all)

Where do these people who have no physics education get the hubris to criticise the consensus views of the physics community? Is it the same place the anti-evolution people get their hubris? Do they realize how unlikely it is that their layman's complaints are correct? They must not. If you think that you know how einstein was wrong with Relativity, and have no physics education, or if you think you know how darwin was wrong with evolution, and have no biology education, reconsider your belief.

Steve, knowledge has no bearing on... ... ...dilation of his own gravitational field. ... ...only by their own subjective Truth.

So, then what you are saying is that the clock on top of Mt. Everest is running faster, but time isn't. If it were time that was running faster, then events (i.e. sunrises, sunsets) would keep in synch with the faster running clock. Where do these people who have no physics education get the hubris to criticise the consensus views of the physics community? Is it the same place the anti-evolution people get their hubris? Do they realize how unlikely it is that their layman's complaints are correct? They must not. If you think that you know how einstein was wrong with Relativity, and have no physics education, or if you think you know how darwin was wrong with evolution, and have no biology education, reconsider your belief.

Read a book or two about relativity. or the relevant chapters from a textbook of Modern Physics. Or check out any number of websites. Or ask Paul.

OK Steve, if a clock is running faster, but events don't keep in synch with the faster moving clock, then how is this different from simply having a fast running clock?

Ah, I see. Time goes faster as you get older because your mass increases. But wouldn't days sitting on top of Mount Everest be interminably long?

I apologize if this is an ignorant question, but...

Isn't the speed of light in any medium (including a vacuum, which I probably shouldn't be calling a medium) dependent on the permittivity and permeability of that medium? The permittivity in a vacuum is supposedly due to the virtual particle-antiparticle pairs that occur in it, which can absorb and re-emit photons. If there are less particle-antiparticle pairs, then there should be a lower permittivity, and higher speed of light.

There was a paper by a Klaus Scharnhorst on it ( http://arxiv.org/abs/hep-th/9810221 ), but I don't believe I know enough about physics (alas, I am only a layman) to judge the hypothesis. But I've read elsewhere that there was a measured difference in the speed of light (didn't get the exact measurement).

I'm wondering if Scharnhorst's hypothesis is valid, and how Special Relativity works out if the speed of light can be made faster or slower?

Again, I apologize if this is an ignorant question.

Yes, just as being a vegan teetotaler causes time to move very slowly. You don't actually live longer, it just seems like it. And you don't enjoy the time you do live. As the saying goes, time goes faster when you're having fun.

OK Steve, if a clock is running faster, but events don't keep in synch with the faster moving clock, then how is this different from simply having a fast running clock?

—

Although I would hesitate to call Mr. Richards an arrogant moron, mainly because I have no evidence whatsoever that he is arrogant, I do find his "analysis" to be both ethically and intellectually bankrupt. Personally, I have no interest in vacuuous rantings as posited by Mr. Richards who evokes only two emotions: laughter and pity. Aside from the sport, I fail to understand why we joust with such intellectual lightweights as Richards.

All this blather reminds me of the 1986 Challenger report in which Richard Feynman said, essentially, that it doesn't matter what the committee decides by vote, the fact is that if the shuttle is launched in freezing weather it will blow up. Physics trumps policy.

It doesn't matter what Dembski or Behe or Wells or any of the IDiots say, the Universe is the way it is. Physics trumps ideology.

Professor Perakh,
You are right to the extent that the childish grasp, no, not grasp, the misunderstanding of these loons makes any form of discussion an endeavour bound to be mired a host of problems...
And yet, the general public (of which I certainly am, although I did take four semesters of college Physics) has _no_one_ but the most learned, such as yourself, to rely upon.
As far as I can tell the anti-scientific/pro-religious sentiment is reaching all time highs, and is empowered by the wealth and power of the American State. Ggabo of Cote D'Ivoire, for example, at least _pretends_ to be a religious nut for the money/political leverage.
I sympathize with your wishing these morons away, but I believe it is your duty to society itself which demands that you, instead, confront them.
Or, if you have the means, pay someone to do it for you.

When I was a teenager and slightly older I had no problem with getting rid of absolute time and I did not mind an expanding universe one bit and I was willing to give Albert Einstein the benefit of the doubt given that his theories have stood the tests of time, criticism and rigorous experiments. I set off to see if I could get a handle on the theories of Relativity. Sure, I had no hope of getting into the math but there were plenty of laymen type books at the library; I had always loved science. How hard could it be?

Several books later and after three periods of giving up, I got to the point where it all seemed to make sense. My point is that, while you can get a simple understanding of the theory without having the math to actually use it to do science, it requires finding a few good books and slogging through. An online discussion may be helpful but it won't give you a good understanding of the theory. I would also suggest approaching the subject as if it were true while learning about it.

If you can accept a theory temporarily you can ask if it makes sense AFTER you understand it. If it does not make sense, you have the knowledge to state why. That is one reason why none of these Panda's Thumb people ever get converted or even "baffled/silenced". They have looked into all the "theories" (meaning the one theory that evolution is not true) and found the consequences to be ludicrous in the face of the observable evidence and reason. Creationism when combined with knowledge form many branches of science draws the conclusion of a God who makes mistakes and oversights when he creates. It requires a God who plants false evidence and needless coincidences which support evolution in every layer of reality to make us doubt him and who sees faith in things that are perfectly designed by him to look false as a positive thing. While it may be consistent with the God of the "scriptures", it is a nightmare belief for a thinking human being.

However, I think I see the point he is trying to make. It is true that an observer moving at a speed near the speed of light relative to Earth would in fact measure a very small time since the big bang.Vic Stenger

Different speed of time on the sea level/Mount Everest is a prediction of General Theory of Relativity. I think that it's neccessary to understand the Special Theory before one tackles this one.

And the Special Theory, as I understand it (and I might be wrong), has only two prerequisites:

1. All frames of reference for observers that travel at uniform velocity relatively to each other are EQUIVALENT (i.e. there is no way how to ascertain if your frame of reference is in rest or uniform motion, unless you look out).

2. Speed of light is constant in every frame of reference.

It's this second notion that is hard to grasp, since it has lots of counter-intuitive results.

General Theory of Relativity adds a third prerequisite which I think goes something like that:

3. A frame of reference undergoing acceleration due to gravitational force is indistinguishable from the frame of reference that is in rest or uniform motion. (again, this holds for observer IN the frame).

Is this generally or specially correct?

I fail to understand why we joust with such intellectual lightweights as Richards... It doesn't matter what Dembski or Behe or Wells or any of the IDiots say, the Universe is the way it is. Physics trumps ideology.

— Bill

Is it not that a frame of reference undergoing (a given) acceleration is indistinguishable from a frame of reference "at rest" but subject to (a given) gravitational force? Or conversely, freefall in space is actually inertial motion while "standing still" on the earth's (or technically something massive that isn't spinning's) surface is accelerated motion.

Isn't the speed of light in any medium (including a vacuum, which I probably shouldn't be calling a medium) dependent on the permittivity and permeability of that medium? The permittivity in a vacuum is supposedly due to the virtual particle-antiparticle pairs that occur in it, which can absorb and re-emit photons. If there are less particle-antiparticle pairs, then there should be a lower permittivity, and higher speed of light. There was a paper by a Klaus Scharnhorst on it ( http://arxiv.org/abs/hep-th/9810221 . . . ), but I don't believe I know enough about physics (alas, I am only a layman) to judge the hypothesis. But I've read elsewhere that there was a measured difference in the speed of light (didn't get the exact measurement). I'm wondering if Scharnhorst's hypothesis is valid, and how Special Relativity works out if the speed of light can be made faster or slower? Again, I apologize if this is an ignorant question.

— Malkuth

These ID proponents would do well to take the Annenberg/CPB video class "The Mechanical Universe" in it's entirety. These classes are available online, are free, and illustrate Einstein's and others theories perfectly. To prove if they understand the material, ask them if they would like to retract their statement. If no, then its back to class. Lather, rinse, repeat.

There is an unwritten law regarding kooks. Sure signs you are reading nonsense from a kook are when they claim a) Einstein was wrong, or b) there is a lumineferous ether.

"Physics is just a bunch of theories."

Those Annenberg/CPB tapes are usually very expensive. I'm not sure if they are free to certain, qualifying academic institutions or not, but I had to pay 45$ plus shipping for one episode of one of the math shows.

If the universe if 13.7 billion years old from our reference frame, from where does the universe appear oldest? What would that time mean? Would there be some utility to finding what time this was?

Does Netflix have the Annenberg/CPB tapes? That would reduce costs substantially.

Re "3. A frame of reference undergoing acceleration due to gravitational force is indistinguishable from the frame of reference that is in rest or uniform motion. (again, this holds for observer IN the frame)."

Add one condition here: acceleration pushes the whole object in the same direction. Gravity pulls the whole object toward a point, which means that it also, to some extent, pulls the sides of the object toward each other. If the object is large relative to the distance from the gravity source, that effect could be measurable.

Henry

It seems that no one has taken up your question yet. It's not ignorant. The first time I saw an index of refraction curve for a glass that dipped below 1, I had the same question. I found a pretty good article that doesn't get too in depth here that will probably help you out.

— GCT

I wonder if that ties in with something I read a few months ago, about the speed of light varying a very slight amount with frequency. Would some frequencies be more prone to absorption/reemission than others? (I forget which end of the spectrum it said was slower than the other.)

Henry

Um, correct me if I'm wrong, but didn't Einstein just pick a very large number? Is the speed of light actually relevant to the equation?

Ed, which equations are you referring to? E = m*c^2? Gamma = 1/(c^2 - v^2)? (I may have that one wrong, but it definitely has a c in it.) C comes up in many equations of relativity.

Oh, and while it's true that gravitation from a point source looks different than acceleration to something large and close to the point source, that's not really important, since it would be most accurate to say that in general, gravitation from a planer source is indistinguishable from acceleration, and the point source is a degenerate case.

And I'm fairly certain that the speed of light is computed with the vacuum permittivity in mind, so that it assumes absorption/re-emission from virtual particle/anti-particle pairs. Either that, or the virtual particles don't absorb light, but I doubt it.

As for the age of the universe: It really doesn't matter how old the universe appears in other reference frames. If you had been constantly accelerating (or in a deep gravity well) since the Big Bang, you'd think the universe was a lot younger than we on Earth do; this would have no importance for cosmology. For someone to think the universe is older than we on Earth do, they'd need to have been in constant motion (i.e., not accelerated and not in a gravity well) for all time; I'm not sure how much longer they'd think the universe is, but again, it really doesn't matter.

Disclaimer: I'm not claiming to be an expert on this, so anyone can correct me if I'm wrong, but here goes.

Malkuth, I believe that c is always 3x10^8, which is the speed of light in a vacuum. I don't think that one can slow down light in a vacuum.

Henry J, the index of refraction does vary depending on frequency, which does affect the speed of light traveling through a medium. Usually, it's said that the light travels at the speed c/n (which is the phase velocity I believe.) I'm not sure if some frequencies are more prone that others per se; I think it depends on the material the light is propagating through.

Oops, bad scientist...that's c=3x10^8 m/s.

I believe that higher frequencies of the EM spectrum experience a greater decrease in velocity and thus refractive indices increase with frequency. I'm not sure though...

"If the universe if 13.7 billion years old from our reference frame, from where does the universe appear oldest? What would that time mean? Would there be some utility to finding what time this was?"

While I can't answer your question, the problem I have as a non-physicist answering your question might be helpful. The problem I have is that I ask myself "oldest compared to what?" Remember that relativity says that two people passing by each other in space at near light speed will BOTH see the clocks of the other as being slow. Now, if I wanted to think of what would experience the universe as being really really old, I'd want to pick a vantage point from which the universe's speed appeared to be at a maximum to myself. Imagine if I wanted to see a clock on a certain train as going the slowest as possible from the vantage point I pick. I could pick a point along the path of the train, but what if the path is moving too (say, the train is on an asteroid zooming through space). So maybe I could pick a point in space on which both the train and the asteroid its on appear to be moving. That would make the train appear to be going REALLY fast, and its clock really slow. I could even move myself in the opposite direction of the asteroid and the train. But for the universe, where in the heck would that place be? How would I move? The universe is expanding away from me EVERYWHERE, from ANY point I pick. So I wouldn't be able to play the same tricks to make it look faster (and hence slower) to myself.

Maybe that was all wrong and goobledygook, but for an amatuer trying to think about relativity, that's why the question ties my head in knots.

Which is exactly why I'm not likely to be the sort of person who goes "I think I just disproved Einstein!"

I was talking about through space, not through what we think of as a medium. Some article gave the idea that light from other galaxies might show a slight difference in arrival time based on its frequency. I don't know if the idea held up or not (or whether it's even been tested). Also don't know if it was based on there being some interference from particles along the route, whether scattered matter or the occasional virtual particle.

Re: Comment 23680 by Josh Narins.
Dear Josh: I agree with you that exprts indeed must spend some time and effort explaining to laymen the basic facts of science. I believe, though, that I have a valid excuse for not actively taking part in the discussion on this thread. I have had a surgery recently and it is difficult to me to type as my shoulder is bandaged.

Regarding my general obligation to share my experience with general public, perhaps it is relevant to point out that I am over 80 years old and that when I already was 80, I wrote and published a book over 400 pages long (titled Unintelligent Design) where I did my best to reveal the emptiness and futility of the ID concepts.

Since there are many well substantiated comments on this thread elucidating various subtleties of relativity, I'll comment now on only one question asked by Enigma (comment 23608) to which nobody has so far offered a response. First, zero Celcius is not the absolute zero but 273.16 Kelvin above absolute zero (or you can say that absolute zero is at -273.16 Celsius). Second, even at absolute zero of temperature the particles (such as electrons) possess energy which is not zero (it is callled the ground state - which is the minimal energy a particle can possess). Furthermore, absolute zero is unattaninable (the 3rd law of thermodynamics) although it can be approached infinitely close. What is zero at absolute zero of temperature is the system's entropy (although it is just a theoretical limit as the absolute zero is practically unattainable).
Cheers, Mark Perakh

Re "I believe that higher frequencies of the EM spectrum experience a greater decrease in velocity and thus refractive indices increase with frequency. I'm not sure though..."

That would make sense I guess, if one presumes that each wave cycle has an equal chance of interacting with a real or virtual particle that happens to be at that location, so more waves per unit distance = greater slowdown.

---

I wonder if a clock (or any physical process) deep inside the Earth would run faster or slower than the same thing sitting on Earth's surface. (Weight drops as one goes from surface toward the center; something at the center is pulled equally in all directions and thus weightless, even if squashed from all the pressure.)

Henry

A clock at the center of the planet would indeed run faster than one on the surface -- at least, based on the GR effects. If you're comparing it with a clock on the equator (or anywhere that's not a pole, really), you've also got SR effects, and need to ask which frame you're looking from.

Realistically, though, the difference would only matter if you're trying to position satellites or something, which isn't likely to happen at the center of the Earth.

So a rise in sea level to closer to Everest would give us longer days. Is this a reason for defending, or attacking, global warming?

Let me wade in here. First, I've read Richards' article (listed somewhere above), and it appears that he misunderstands what is meant when it is stated that there is no "absolute time."

To have "absolute time", you need an "absolute" frame of reference. Einstein's theories (both special and general) start with the premise that (1) there is NO "absolute frame of reference", and hence (2) all is relative. To deny that there is no "absolute" time, is not to deny that something such as "time" exists. So Richards just simply misunderstands what Einstein was after. I can't defend that. But, judging from the posts, it seems like a lot of people don't understand Einstein either. This is not surprising, and should not be used, IMHO, against Richards like a dagger.

Further, let me point this out. The idea that Einstein had concerning the absence of "absolute" frame of reference came from science's begrudging abandonment of the idea of an "ether", which was so central to the work of Maxwell on electricity and magnetism. The coup de gras that "axed" the "ether" was the Michelson-Morley experiment, ca. 1875. That experiment purportedly showed that light travels at the same speed no matter at what its direction relative to the supposed "ether." Interestingly, in the latest two issues of New Scientist, there have been two articles dealing with the possible reemergence of the "ether", one article dealing with a proposed experiment to double check the Michelson-Morley experiment.(and which talks about seemingly valid mathematical arguments disputing Michelson-Morley's results.)

I personally find it very hard to believe that something like an "ether" doesn't exist. But even if an "absolute frame of reference" exists, that doesn't mean that Einstein's theories are wrong; only that they have to be reformulated. Einstein assumed that space was both "homogeneous" (i.e., the same everywhere) and "isotropic" (i.e., there is no preferred 'direction). If there is an "ether", then "isotropy" has to go; but the theories do not!

Here's what Einstein himself had to say about this: (from "The Meaning of Relativity")

"The laws of physics could be expressed, even in case there were a preferred direction in space . . . If there were a preferred direction in space it would simplify the description of natural phenomena to orient the system of co-ordinates in a definite way with respect to this direction. But if, on the other hand, there is no unique direction in space, it is not logical to formulate the laws of nature in such a way as to conceal the equivalence of systems of co-ordinates that are oriented differently." (p. 16, footnote)

A clock at the center of the planet would indeed run faster than one on the surface...

— Randall Wald

"I personally find it very hard to believe that something like an "ether" doesn't exist."

Wow! Just submit that brilliant sentance to a journal of physics as an entire article, and you're set for life. Nobel Prize for you!

plunge,

You shouldn't be so sarcastic. The Higgs field is very aether-like.

Would the 'c' that's to be used in Einstein's equations be the speed of light if there were absolutely nothing interrupting the light, then? That is, the speed at which a photon travels without being absorbed and re-emitted by virtual particle-antiparticle pairs? Rilke's Grand-daughter had said that it's photons that always move at the constant speed of light, but not necessarily "light" because the constant-speed photons can be absorbed and re-emited by atoms in a medium (which takes time). Could the same thing by said of a vacuum? That, because a vacuum has virtual particles and antiparticles which "slow" light, the speed of light in it is not necessarily equal to the constant speed of a photon? Or am I incorrect in assuming that the virtual particle-antiparticle pairs absorb and re-emit photons?

If the universe if 13.7 billion years old from our reference frame, from where does the universe appear oldest? What would that time mean? Would there be some utility to finding what time this was?

So a photon climbing up the well from the centre of gravity to the surface would have a lower frequency at the surface than that observed at the centre. Clocks at the centre would therefore have a similarly lower frequency, i.e., run slower, when observed from the surface.

— Zim

Don't look now, but that ID post on Einstein has just been "disappeared".

... that ID post on Einstein has just been "disappeared".

Re "So a rise in sea level to closer to Everest would give us longer days."

By a tiny fraction of a second. Hardly relevant to climate change.

---

Re "That experiment purportedly showed that light travels at the same speed no matter at what its direction relative to the supposed "ether.""

Didn't the math imply that, even before the experiment was performed? As I understand it, the equations for EM could (even then) be solved for c, and the solution came out as a constant.

---

Henry

This is a highly nontrivial question. First of all, what are those virtual particles? In a quantum field theory you have a set of interacting fields, their excitations with a given energy and momentum can be interpreted as particles. Because this is a quantum theory, you can set up the particles and then observe the result, but there is not too much sense in asking how exactly they interacted. The probability of the outcome is a result of a calculation where all possible intermediate states are taken into account. These are the virtual particles. The question whether photons really propagate at 'c' is equivalent to whether this effect causes photons to effectively gain mass. The result of the calculation, part of a program called renormalization, is that though the contribution of the virtual intermediate states renormalize the electromagnetic field, they give no mass. The reason can be tracked back to the gauge symmetry on which the electromagnetic interaction is based. So, both the underlining field and the observed photons are massless in Quantum Electrodynamics. Of course, as always in science, future discoveries could change things, but this is our current theory which agrees with experiment very well. In the other case, the speed of light would indeed slightly depend on frequency.

— Koly

Yes, exactly. The red shift does not depend on the stregth of the gravitational field, but rather on the potential. More accurately on the time-time element of the metric tensor. So indeed, in the center of the Earth the time would be ticking slower, even when there is no gravitation there.

— Koly

Seems like at the center of the planet, the "slope" of the gravity well would be zero. But if clocks (i.e., any physical process) run slower there too, it kind of undoes my previously mentioned way of understanding the time slow-down at or above the surface of the planet. (That is, in the middle of the planet, photons don't have to travel a longer distance to get from atom to atom, so that can't be used to explain the time dilation there.)

Henry

Don't look now, but that ID post on Einstein has just been "disappeared".

Is your depth in a gravity well the important thing, or is it the slope of the well at your point? (Actually, that last sentence may not make sense, but it sounds cool.)

— Randall Wald

It's unfortunate, then, that my understanding of quantum mechanics is only trivial. From my understanding, there are particle-antiparticle pairs that appear in a vacuum and exist for an incredibly short amount of time, after which they annihilate with each other. They can also exist in the intermediate stages of a phenomena, but don't exist in the initial or final state, which is why they're called virtual particles. At least, to my trivial understanding. Is this at all correct?

— Malkuth

Hmm. That seems counterintuitive, at least. I know that a clock closer to a black hole will tick more slowly than one distant from the black hole. Still, isn't the person at the center of the earth allowed to think that he's floating in open space? I mean, how could he tell either way? Perhaps my problem is that I'm viewing things too absolutely; I think that to figure out your clock's rate, you need only calculate how much acceleration/gravity you're feeling, and you know how your clock ticks with respect to an open-space (no acceleration) clock. Is your depth in a gravity well the important thing, or is it the slope of the well at your point? (Actually, that last sentence may not make sense, but it sounds cool.)

— Randall Wald

Well, and please ignore my spelling and grammar errors, my English still doesn't seem to be up to par...

Comment #23933 Posted by Matt Young on April 8, 2005 02:43 PM (e) (s) Don't look now, but that ID post on Einstein has just been "disappeared". It was there a minute ago, with an update.

Let me clarify: I can fully understand why a person near a black hole thinks his friends in open space appear to have faster clocks. After all, the light he sees coming from them has been blueshifted. To use specific numbers, suppose they thought the light had a frequency of 2*10^15 Hz, and he thinks it has a frequency of 4*10^15 Hz. Frequency is cycles per second, so (dropping the 10^15 for clarity), an event which happens four times per our near-black-hole observer's second happens two times per our open-space observers' second. Thus, we see that the open-space observer's clock is twice as fast as the near-black-hole observer's clock. Anyway, the point is I get the basic concept of time running at different speeds because of gravity wells.

The only problem I have is with the center of the earth. In particular, I believe (or at least, feel intuitively) that since the middle of the earth feels no gravity, it should be equivalent to open space, and should have a clock that runs at the same rate as an open-space clock. Let's imagine that our center-of-earth observer has a long tube which goes to the surface and beyond, until there's no more effect of earth's gravity (which would take forever, but you get the idea). At the other end is a second observer. Can these two observers figure out which one is in the center of the earth and which one is in open space? If not, then how can the person in the center of the earth have a slower clock than the person on earth's surface, who would feel a gravity well (just like the person near the black hole)? Shouldn't the person in the center of the earth have a faster clock? This is the question I don't understand.

Re "Shouldn't the person in the center of the earth have a faster clock? This is the question I don't understand."
I don't understand the mechanism behind the effect, either, but I think it would cause inconsistencies if clocks started going faster as one went deeper under the surface.

It's not just time that's warped, either - distance is contracted; the distance from surface to center is a bit more than would be expected if space obeyed Euclid.

One thought I'm having on the matter, is maybe descending into a gravity well reduces the rest mass of matter particles, and maybe the energy that's no longer tied up in mass form might be what goes into the kinetic energy as the falling object speeds up? If the particles in the lower altitude object have less mass energy, then an incoming photon would have more energy relative to the mass energy of those particles. I wonder if that thought is consistent with the math?

Henry

I wonder - how about the common (i.e. non-gravity) blue shift? If I travel directly to some place at fast speed, wouldn't the same logic tell me that time is speeding there (while, according to STR, you can't see any moving object experiencing faster time than yourself). As far as I understand it, the effects of light shift can be accounted for in STR, leaving clean time dilation as a result, but I would appreciate some thoughts on that.

The only problem I have is with the center of the earth. In particular, I believe (or at least, feel intuitively) that since the middle of the earth feels no gravity, it should be equivalent to open space, and should have a clock that runs at the same rate as an open-space clock.

I remember from my basic physics class that under Genral Relativity, a clock at the top of an accelerating rocket ship runs *faster* than a clock at the bottom, even though both clocks are accelerating at the same speed.

The way I like to think of it is that light forces time to slow down in order to turn what ought to be a speed increase of falling photons into a blue shift.

Marek, I am not a physicist, but here goes. First of all, I'd say that the effects of red shift due to time dilation and blue shift due to length contraction will cancel each other out.

Second, if you think about it, as you observe an object you're moving towards, you observe their time running faster, hence a blue shift, and you observe time runnng slower in objects that are moving away from you, hence the red shift.

let's say you're moving between two planets at half the speed of light. Normal time dilation effects for oberving both planets are the same: they both appear to be about 80 something percent of normal speed.

Except they don't. The planets are half a light year apart, and at the end of the years travel time, you've ovserved 2*80% years on planet two, but only 0.5*80% years on planet 1. So, you see double the frequency from planet two, but you also see their clocks running twice as fast. You see half the frequency from planet 1, but you also see their clocks running at half speed.

Thanks for the example, Boronx. Now that I think about it, I remember the accelerating spaceship example from an excerpt of a Feynman lecture I once read. That shows my naive "acceleration directly relates to clock speed" idea can't be all right, and is probably mostly wrong. I probably should think more carefully about what exactly happens to light traveling between the surface and the center of the earth, and then figure out what that implies about clock speed.

Well, that doesn't make sense. Let's say your spaceship leaves planet 1 at year 1. At that moment it's seeing light from planet 2 from year 0.5. When you reach planet2 at year 2, you're seeing light from planet 1 from year 1.5. That says to me that you've observed 1.5 years of planet 2 in your 1 year of travel, not 2. And I guess, if I think about the doppler effect, blue shift at 0.5c would be 50% increase in frequency, not 100%.

I made a mistake. Let's say your spaceship leaves planet 1 at year 1. At that moment it's seeing light from planet 2 from year 0.5. When you reach planet2 at year 2, you're seeing light from planet 1 from year 1.5. That says to me that you've observed 1.5 years of planet 2 in your 1 year of travel, not 2. And I guess, if I think about the doppler effect, blue shift at 0.5c would be 50% increase in frequency, not 100%.

Randall, Henry,

you don't seem to like my analogy with kicking the ball out of the hole. But that's really what's going on, exactly the same thing happens to photon wavelengths as to ordinary matter. It's all only about loosing or gaining energy and momentum.

Imagine this - would a ball thrown out of the center of the Earth slow down or accelarate? Why do you then cannot accept that a light looses some energy too (=red shift)?

The only problem I have is with the center of the earth. In particular, I believe (or at least, feel intuitively) that since the middle of the earth feels no gravity, it should be equivalent to open space, and should have a clock that runs at the same rate as an open-space clock.

— Randall Wald

The only problem I have is with the center of the earth. In particular, I believe (or at least, feel intuitively) that since the middle of the earth feels no gravity, it should be equivalent to open space, and should have a clock that runs at the same rate as an open-space clock.

— Randall Wald

Doh! So sorry about that Double now Triple Post! Feel free to delet either! And this one too.

I am not a physicist, but why do you say that the middle of the earth feels no gravity? Doesn't it feel gravitational acceleration the same as any other point? The exact center may feel it in all directions at once, resulting in no movement, but that is not the same, is it?

Now if you really want a messed-up brain, consider the following true statement:

If the earth contained a hollow cavity in the center, you could float around, feeling no force, anywhere in the cavity, not just the very center.

I do not suggest getting stuck on that idea, it's not possible to understand without spending some time understanding things like Gauss's Law, and other tedium.

Re "If the earth contained a hollow cavity in the center, you could float around, feeling no force, anywhere in the cavity, not just the very center."

Depends on the size of the cavity. At a mile from the center, for example, there'd be somewhere around 1/4000 of a G force toward the center. Not much, but not zero.

Henry

Oops, cancel my last post. I just remembered that with a hollow spherical cavity centered at the center, well, it's the part "under" one that generates the net gravity. The 1/4000 is approximately what one would feel if in a tiny (hopefully air conditioned) cavity offset from the center by a mile.

Henry

Oops, cancel my last post. I just remembered that with a hollow spherical cavity centered at the center, well, it's the part "under" one that generates the net gravity. The 1/4000 is approximately what one would feel if in a tiny (hopefully air conditioned) cavity offset from the center by a mile.

Henry

Oh great, now cancel one of the two cancellations of the aforementioned post... Good grief.

I do not suggest getting stuck on that idea, it's not possible to understand without spending some time understanding things like Gauss's Law, and other tedium.

— Steve

Please edit my non-sentence in the post above by joining the paragraphs beginning "Case 2. If the ...." and "Since the force ...." to read:

... by r_far^2, and since the force is ...

Thanks.

FH