• [deleted]

Rate x Time cannot = Distance in an expanding universe

RxT=D is faulty

The equation is: Could you pick up on CIG theory's concepts as to:

What the true equation for distance is, taking into context CIG Theory.

My math is horrible. My physics worse, however, we go forward.

So, Distance = Rate multiplied by Time (Standard equation)

We now add that new spatial manifestation to this distance as follows:

True Distance = Rate multiplied by Time The % of "c" times the massive quantity in motion, using the atomic mass unit to spatial quantity manifestation in CIG Theory, or, for varying rates of "c", need an exact equation, as my math falls short here.

I quit (bad math).

The result would be the true "Distance" equation and could be used to compare against Red Shift data & predict Red Shift observations, especially anomalies.

Please read CIG in its entirety first.

Note that I don't know how "quickly" a massive quantity turns to a spatial volume.

If instantaneous ( I highly doubt) , then the above notes work as is.

For instance, D = RT function of % "c" x atomic mass unit to spatial manifestation (per CIG) x MASS of unit underway.

Don't forget that for more than one entity, (think bubbles upon bubbles) receding from one location (say EARTH), and each other, we have to add these two (or more) distances together to obtain the accumulated distance( reason for accelerating Universe). Try finding this equation, please.

Please work on the equation.

You will be obtaining the actual and true "Distance Equation".

Use the CUPI quantification from CIG Theory -- www.CIGTheory.com

THX

doug

6 months later
  • [deleted]

Lee Smolin,

You were given FQXi money to restore the "real and global time" and show what's wrong with relativity:

"Many physicists argue that time is an illusion. Lee Smolin begs to differ. (...) Smolin wishes to hold on to the reality of time. But to do so, he must overcome a major hurdle: General and special relativity seem to imply the opposite. In the classical Newtonian view, physics operated according to the ticking of an invisible universal clock. But Einstein threw out that master clock when, in his theory of special relativity, he argued that no two events are truly simultaneous unless they are causally related. If simultaneity - the notion of "now" - is relative, the universal clock must be a fiction, and time itself a proxy for the movement and change of objects in the universe. Time is literally written out of the equation. Although he has spent much of his career exploring the facets of a "timeless" universe, Smolin has become convinced that this is "deeply wrong," he says. He now believes that time is more than just a useful approximation, that it is as real as our guts tell us it is - more real, in fact, than space itself. The notion of a "real and global time" is the starting hypothesis for Smolin's new work, which he will undertake this year with two graduate students supported by a $47,500 grant from FQXi."

What's happened? FQXi money's gone, Divine Einstein, yes we all believe in relativity, relativity, relativity?

Pentcho Valev

    • [deleted]

    Lee Smolin: "The second postulate of special relativity, which says that the speed of light is universal, appears to be almost contradictory in itself. Why? Consider a single photon, tracked by two observers. Assume that the two observers move with respect to each other. If they measure the speed of that single photon, we would normally expect them to get different answers, because this is the way normal objects behave. If I see a bus pull ahead of me at what looks to me like a speed of 10 kilometers an hour because I am in a car screaming down the highway at 140 kilometers per hour, an observer standing on the side of the road will see the bus moving at 150 km/hour. But if I observe a photon under the same circumstances, special relativity says that the roadside observer will measure the photon to have the same speed that I think it has. So why is this not a contradiction? The key is that we do not measure speed directly. Speed is a ratio: it is a certain distance per a certain time. The central realization of Einstein is that different observers measure a photon to have the same speed, even if they are moving with respect to each other, because they measure space and time differently. Their measurements of time and distance vary from each other in such a way that one speed, that of light, is universal."

    But different observers measure the photon to have different frequency, and the frequency is proportional to the speed. So? Isn't it reasonable to assume that, by measuring the frequency, observers indirectly measure the speed? A positive answer was given in my essay:

    Shift in Frequency Implies Shift in Speed of Light

    Pentcho Valev

    • [deleted]

    Lee Smolin, The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, p. 226: "Einstein's special theory of relativity is based on two postulates: One is the relativity of motion, and the second is the constancy and universality of the speed of light. Could the first postulate be true and the other false? If that was not possible, Einstein would not have had to make two postulates. But I don't think many people realized until recently that you could have a consistent theory in which you changed only the second postulate."

    Here is the second postulate:

    "...light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body."

    The gist is "independent of the state of motion of the emitting body" so any non-phony alternative must involve "dependent on the state of motion of the emitting body".

    Pentcho Valev

    8 days later

    William H. Cantrell, Ph.D., Time Dilation: "There is absolutely no argument that time-keeping mechanisms do slow down when moving at high speed, and that in most instances, they obey the time dilation formula of Lorentz and Poincaré. (There are violations, as Jefimenko[10] has pointed out.) The dissident argument here is really more of a metaphysical one. A distinction should be made between Universal absolute invariant time and gravitational effects acting on time-keeping mechanisms such as water clocks, grandfather clocks, digital watches, radioactive decay rates, and cesium clocks (cesium atoms), to name just a few. All sources of oscillation in nature are influenced by a change in gravitational potential. To build a clock, we have no choice but to exploit oscillator sources. Unfortunately we cannot construct an ideal clock [one that cannot be influenced by a change in gravitational potential] even if we use cesium atoms by definition. This was aptly demonstrated by the famous Häfele-Keating experiment[11,12] in which cesium clocks were flown around the world. The atomic clock transported eastward lost 59 ns, while the atomic clock transported westward gained 273 ns, compared to the stationary laboratory standard. All physical devices used for time keeping are subject to error when accelerated, decelerated, or constrained to move linearly through a variation in gravitational potential. The Häfele-Keating experiment is not a failure for relativity theory, but the question should be asked: Is time itself dilated, or are internal processes merely altered by moving through a gravitational field? Metaphysically speaking, we do not consider this to be a distinction without a difference."

    THERE IS NOT A SHRED OF REAL EVIDENCE IN FAVOR OF TIME DILATION, AS OPPOSED TO CLOCK RETARDATION: "Einstein is praised for having made a "leap of faith" beyond the pedestrian reasoning of Lorentz and others, by claiming that when clocks slow down in a relativistic fashion, it is really time itself that is slowing down. But every bit of alleged evidence proves, at most, nothing more than that the clock slows down. Too many physicists subscribe to the belief that there is nothing to time except what can be seen on the face of a clock; but that amounts to the ridiculous statement that a measuring device has been built to measure nothing but itself. This view is an extreme version of operationalism, a very simplistic version of Machian positivism. So the "leap of faith" claiming time dilation remains totally unsupported by facts; mere speculation, not science." -- www.worldnpa.org/site/principals

    Time is not a physical dimention we could travel in.

    Time does not slow down -- "Time Dilation" is not a physical phenomenon.

    Thank you,

    Zbigniew http://www.worldsci.org/people/Zbigniew_Modrzejewski

      • [deleted]

      Zbigniew,

      It is a direct consequence of Einstein's 1905 light postulate (derived in all textbooks) that the clock on the train runs slower than clocks on the ground. Whether you call this time dilation or clock retardation is immaterial. The only reasonable question is: Does the clock on the train really run slower, in accordance with the formula given by special relativity? If your answer is yes, you are 100% Einsteinian. If your answer is no, you are 100% Newtonian.

      Pentcho Valev

      10 days later
      • [deleted]

      Lee Smolin: "Quantum mechanics was not the only theory that bothered Einstein. Few people have appreciated how dissatisfied he was with his own theories of relativity. Special relativity grew out of Einstein's insight that the laws of electromagnetism cannot depend on relative motion and that the speed of light therefore must always be the same, no matter how the source or the observer moves. Among the consequences of that theory are that energy and mass are equivalent (the now-legendary relationship E = mc2) and that time and distance are relative, not absolute. Special relativity was the result of 10 years of intellectual struggle, yet Einstein had convinced himself it was wrong within two years of publishing it. He rejected his own theory, even before most physicists had come to accept it, for reasons that only he cared about. For another 10 years, as others in the world of physics slowly absorbed special relativity, Einstein pursued a lonely path away from it."

      Lee Smolin,

      "Within two years of publishing" special relativity Einstein realized the speed of light varies with the gravitational potential:

      John Norton: "Already in 1907, a mere two years after the completion of the special theory, he [Einstein] had concluded that the speed of light is variable in the presence of a gravitational field."

      It is easy to show that, if the speed of light varies with the gravitational potential, then, relative to the observer, it varies with the speed of the observer. So you are right - in 1907 Einstein did already know special relativity was wrong.

      Pentcho Valev

        a month later
        • [deleted]

        Lee Smolin: "The scientific case for time being an illusion is formidable. That is why the consequences of adopting the view that time is real are revolutionary. (...) Einstein's theories of relativity make even stronger arguments that time is inessential to a fundamental description of the world, as I'll discuss in chapter 6. Relativity strongly suggests that the whole history of the world is a timeless unity; present, past, and future have no meaning apart from human subjectivity. Time is just another dimension of space, and the sense we have of experiencing moments passing is an illusion behind which is a timeless reality. (...) In Part I, I will present the case from science for believing that time is an illusion. In Part II, I will demolish those arguments and show why time must be taken to be real if fundamental physics and cosmology are to overcome the crises they currently face.

        Lee Smolin,

        Special relativity is a deductive theory so if it makes "even stronger arguments" in favour of something that you do not accept, it does so based on some false postulate. Have you identified it in your new book? In a previous book you did expose the false postulate:

        Lee Smolin, The Trouble With Physics, p. 226: "Einstein's special theory of relativity is based on two postulates: One is the relativity of motion, and the second is the constancy and universality of the speed of light. Could the first postulate be true and the other false? If that was not possible, Einstein would not have had to make two postulates. But I don't think many people realized until recently that you could have a consistent theory in which you changed only the second postulate."

        Pentcho Valev

        • [deleted]

        Pentcho,

        Interesting to see Smolin is writing a book on the topic. Physics seems to be swirling around a black hole of suppositon, since many of the previous assumptions are coming to naught.

        He seems to argue time is a foundational vector of events. Not sure how different that really is.

        "Time will turn out to be the only aspect of our everyday experience that is fundamental. The fact that it is always some moment in our perception, and that we experience that moment as one of a flow of moments, is not an illusion. It is the best clue we have to fundamental reality."

        Why not there is only the moment. It changes shape, so there is nothing external to it.

        Minor contradiction:

        "Temperature is just the average energy of atoms in random motion, so the laws of thermodynamics that refer to temperature are emergent and approximate."

        "In the Standard Model of Particle Physics, which is the best theory we have so far of the elementary particles, the properties of an electron, such as its mass, are dynamically determined by the interactions in which it participates. The most basic property a particle can have is its mass, which determines how much force is needed to change its motion. In the Standard Model, all the particles' masses arise from their interactions with other particles and are determined primarily by one -- the Higgs particle. No longer are there absolutely "elementary" particles; everything that behaves like a particle is, to some extent, an emergent consequence of a network of interactions."

        If everything is interconnected, then isn't thermodynamics a manifestation of the "network," from which the properties of the particles are emergent?

        a month later
        • [deleted]

        The Missing Part of the Twin Paradox

        A train is at rest and a clock on the ground is moving to and fro between two clocks situated at the front and the back end of the train. The speed of the moving clock is constant except for the turn-arounds where the clock suffers sharp acceleration. This is the classical relativistic scenario - relativity predicts that the moving clock runs slower than the two clocks at rest on the train.

        In a complementary scenario (which is missing in the relativistic literature), the clock on the ground is at rest but the train is moving to and fro so that the clock on the ground formally commutes between the front and the back of the train as before. Will the clock on the ground run slower or faster than the two clocks situated at the front and the back end of the moving train? What does relativity say?

        A clue:

        Relativity and Its Roots, Banesh Hoffmann, p. 105: "In one case your clock is checked against two of mine, while in the other case my clock is checked against two of yours, and this permits us each to find without contradiction that the other's clocks go more slowly than his own."

        Pentcho Valev

          • [deleted]

          A clock on the ground is at rest but a train is moving to and fro so that the clock on the ground formally commutes between the front and the back of the train. The speed of the train is constant except for the turn-arounds when clocks on the train suffer sharp acceleration. Will the clock on the ground run slower or faster than clocks on the the moving train? What does relativity say?

          First of all it should be noted that the acceleration suffered by moving clocks cannot be responsible for time dilation effects:

          Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."

          It should also be noted that a clock at the front of the moving train coincides with the travelling twin's clock in the classical twin paradox scenario. Accordingly, relativity predicts that the clock at rest on the ground runs FASTER than the clock at the front of the train.

          On the other hand, relativity predicts that, ALL ALONG, observers on the moving train measure the clock at rest on the ground to run SLOWER than clocks on the train.

          This is called REDUCTIO AD ABSURDUM. The underlying postulate, the principle of constancy of the speed of light, is false and should be rejected.

          Pentcho Valev

          Pentcho,

          Your scenario is ok but, 'solution' clearly false. There is a far better one that works, resolving all issues and consistent with ALL observation.

          Each clock appears to run faster when it is approaching the detector, because its sequence of emissions is compressed (blue shifted) or 'contracted'

          Each clock also appears to run slower when receding from the detector, because it's emissions are dilated (red shifted).

          All emissions propagate at c locally.

          Please consider carefully as you will find that simple mechanism resolves all issues in physics. Or respond with why you think may NOT resolve them.

          Peter

            • [deleted]

            Peter

            You may be sayong this, but I am not sure. Nothing is happenng to the emissions (ie light with which the event is observed). Because the light is unaffected by reception (ie seeing). This optical illusion is a function of altering spatial position vis a vis event and recipient observer, and applies to any sequence, not just clocks (time). If the distance is increasing then the time taken for light to reach the recipient will get ever longer, giving the appearance, to the observer, that the sequence is slowing down, and vice-versa.

            Paul

            • [deleted]

            Horrible doublethink in Einsteiniana:

            Accelerations are responsible for the youthfulness of the travelling twin:

            John Norton: "That inertial observers in relative motion will each judge the others' clocks to run slower is, by now, a quite familiar and readily understandable outcome of relativity theory. It does take a little while to get used to the idea, of course. When you first hear it, it seems strange and even paradoxical. How can each be correct in judging the other's clock to have slowed? What would happen if the two observers meet and compare their clocks? If relativity is right, each would have to read a time earlier than other; and surely that is impossible. Or is it? We now know that these concerns are misplaced. The clocks cannot start out from the same place and then be re-united without one or both accelerating; and those accelerations so interfere with the analysis that no contradiction arises. When either accelerates, they cease to be inertial observers. However an enduring literature has tried to generate some sort of paradox from the effect of relativistic clock slowing. The most famous of the these attempts is associated with a story of two twins. One stays on the earth - the "stay-at home-twin." The stay-at-home twin's motion is inertial throughout. The other travels off rapidly into space, journeys far and fast and then returns home. The traveling twin must accelerate to complete this journey."

            Accelerations are not responsible for the youthfulness of the travelling twin:

            Gary W. Gibbons FRS: "In other words, by simply staying at home Jack has aged relative to Jill. There is no paradox because the lives of the twins are not strictly symmetrical. This might lead one to suspect that the accelerations suffered by Jill might be responsible for the effect. However this is simply not plausible because using identical accelerating phases of her trip, she could have travelled twice as far. This would give twice the amount of time gained."

            George Orwell: "Doublethink means the power of holding two contradictory beliefs in one's mind simultaneously, and accepting both of them. (...) It need hardly be said that the subtlest practitioners of doublethink are those who invented doublethink and know that it is a vast system of mental cheating. In our society, those who have the best knowledge of what is happening are also those who are furthest from seeing the world as it is. In general, the greater the understanding, the greater the delusion ; the more intelligent, the less sane."

            Pentcho Valev

            Paul,

            Ergo; If a detector recedes, the apparent rate of time increases, i.e. 'dilates'.

            The 'sample' found by detector APPROACHING a clock then has 'length contracted' waves, so time appears to go faster.

            It's not being able to think past the (derived) concept 'frequency' to analyse the real mechanism that has blinded mankind to nature.

            Now if everybody stuck to above on their walls and thought about it and it's consequences until it made sense, then science could finally move on again.

            An 'inertial frame' is the (relative to a datum) 'state of motion of an 'inertial system' made up of matter. The assignable group 'state of motion' may be like a balloon full of moving gas particles. I've dubbed it a 'virial kinetic entity' (VKE), equivalent to a Hilbert Space, and a 'leaf' in modal logic. The full ontology is the DFM.

            QM? ...Yes the detector IS part of the system. Otherwise there would be no detection.

            Peter

              • [deleted]

              Peter

              "the apparent rate of time increases"

              The key word there is "apparent". That is, what is observed, ie what is received, which in sight is light. But this is not physical existence, it is a physical phenomenon which is caused as a consequence of the existence of the existential sequence (which is what people are normally referring to when they speak of physical reality).

              Nothing is altering in that existential sequence, or in the physically existent representation of it (aka light). What occurs, occurs. That is, the fact that some light may be subsequently received by a sentient organism is irrelevant. Both the existential sequence, which has no interaction with the recipient observer anyway, and the physically existent representation of it (eg light), occur before they are received. Leaving aside the 'enhancements' that sentient orgainsims invoke in the subsequent processing of what was physically received, which is clearly not part of the physical circumstance, the timing difference is a function of the time taken for the light to travel to observers who are in different spatial relationships with that existence. And if those spatial relationships alter whilst the light is travelling, ie there is differential movement, then there is another optical effect. The issue has nothing whatsoever to do with inertial frames, or invoking a constantly altering frame of reference for each stage of the journey that light takes in order to calibrate its speed.

              "QM? ...Yes the detector IS part of the system. Otherwise there would be no detection"

              This is a specific example of the fallacy I am pointing out above. The detector just causes the cessation of the physically existent representation (eg light) in the form as received. Its existence has already occurred, and to be existent, what occurred was definitive. Neither did that interaction involve the existential sequence, it involved light, which with the evolution of sight has acquired a functional role, ie as an independent representation of reality. That acquired role, and the effecting of it, does not alter its physical existence.

              Paul

              24 days later
              • [deleted]

              It seems the official end of Divine Albert's Divine Theory is imminent - hints are seen all over the place:

              "The Crazy Drama of Physics (...) Now when a new scientific development comes along, it's as though terms like "light" and "speed" and "time" are characters in a long-running foreign soap opera. They all have complicated backstories, and the multiple costume changes don't help. At first, "time" was just a simple campesino, but then - twist! - it's revealed that "time" and "space," who we thought was a swashbuckling bandito, are the same person, except then - twist! - it turns out that maybe they're twins, and because one of them was in a spaceship for a while during the third season, now the one that stayed behind and inherited the contessa's fortune is older than he is. (...) If you've managed to wrap your mind around that - the idea that the past, present, and future all exist at once and are therefore immutable and hence there are no surprises and also, by the way, logically no free will - welcome to the current episode, in which we posit that - twist! - time does exist. Lee Smolin's 'Time Reborn: From the Crisis in Physics to the Future of the Universe' claims that now is real, the future hasn't happened yet, and there are genuinely new things under the sun. The contessa and her daughter weren't blackmailing the duke at all, or at least, not with the secret we thought he had. The duke's mad wife was the sane one the whole time."

              Needless to say, the transition to the "current episode, in which we posit that - twist! - time does exist" is essentially a transition from Einstein's 1905 false light postulate to the variable speed of light (c'=c+v) predicted by Newton's emission theory of light.

              Just in case some Einsteinian needs reassurance:

              Gluck - Orfeo ed Euridice - Dance of the Blessed Spirits

              Pentcho Valev

              14 days later
              • [deleted]

              Disgusting Doublethink in Einsteiniana

              "Smolin wishes to hold on to the reality of time. But to do so, he must overcome a major hurdle: General and special relativity seem to imply the opposite. In the classical Newtonian view, physics operated according to the ticking of an invisible universal clock. But Einstein threw out that master clock when, in his theory of special relativity, he argued that no two events are truly simultaneous unless they are causally related. If simultaneity - the notion of "now" - is relative, the universal clock must be a fiction, and time itself a proxy for the movement and change of objects in the universe. Time is literally written out of the equation. Although he has spent much of his career exploring the facets of a "timeless" universe, Smolin has become convinced that this is "deeply wrong," he says."

              "Was Einstein wrong? At least in his understanding of time, Smolin argues, the great theorist of relativity was dead wrong. What is worse, by firmly enshrining his error in scientific orthodoxy, Einstein trapped his successors in insoluble dilemmas..."

              71:04 : QUESTION: What you did not talk about was time dilation, the myth of time dilation, I think that needs to be blown as well. What do you think of that? LEE SMOLIN: I disagree. This is an important point. Special relativity may be superseded but it is holding up enormously well under experiment. Giovanni Amelino-Camelia is here... and he and various friends of ours have been trying to transcend special relativity for years and we are keeping knocked back by experiment... and the experiments have shown that special relativity is true to tremendous precision... Do you agree Giovanni? Yea!

              Pentcho Valev

                • [deleted]

                The doublethink demonstrated above and the lack of any reaction in the scientific community are unmistakable signs of dead science:

                [link:blogs.scientificamerican.com/cross-check/2013/02/04/the-end-of-science-bandwagon-is-getting-crowded/]"The End-of-Science Bandwagon Is Getting Crowded (...) Compare the concerns of Simonton and the Edgeheads to what I wrote 17 years ago in The End of Science. I argued that "given how far science has already come, and given the physical, social and cognitive limits constraining further research, [pure] science is unlikely to make any significant additions to the knowledge it has already generated. There will be no more great revelations in the future comparable to those bestowed upon us by Darwin or Einstein or Watson and Crick." Edgeheads and other pessimists, welcome to the end-of-science bandwagon."[/link]

                In 1954 Einstein himself jumped on the end-of-science bandwagon - he had discovered that his theory was wrongly based on the "field concept":

                Albert Einstein (1954): "I consider it entirely possible that physics cannot be based upon the field concept, that is on continuous structures. Then nothing will remain of my whole castle in the air, including the theory of gravitation, but also nothing of the rest of contemporary physics."

                Formally, Einstein's theory did not start with the advancement of the "field concept" - rather, it started with the advancement of two postulates. Was some of them an offspring of the "field concept"? Clues showing that Einstein's 1905 false light postulate was in fact the mortal sting of the "field concept":

                "The two first articles (January and March) establish clearly a discontinuous structure of matter and light. The standard look of Einstein's SR is, on the contrary, essentially based on the continuous conception of the field."

                "And then, in June, Einstein completes special relativity, which adds a twist to the story: Einstein's March paper treated light as particles, but special relativity sees light as a continuous field of waves."

                Relativity and Its Roots, Banesh Hoffmann: "Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether."

                Pentcho Valev

                • [deleted]

                Another unmistakable sign of dead science:

                The Albert Einstein Institute teaches that the speed of light relative to the observer (receiver) varies with the speed of the observer, in violation of special relativity:

                Albert Einstein Institute: "The frequency of a wave-like signal - such as sound or light - depends on the movement of the sender and of the receiver. This is known as the Doppler effect. (...) Here is an animation of the receiver moving towards the source: (...) By observing the two indicator lights, you can see for yourself that, once more, there is a blue-shift - the pulse frequency measured at the receiver is somewhat higher than the frequency with which the pulses are sent out. This time, the distances between subsequent pulses are not affected, but still there is a frequency shift: As the receiver moves towards each pulse, the time until pulse and receiver meet up is shortened. In this particular animation, which has the receiver moving towards the source at one third the speed of the pulses themselves, four pulses are received in the time it takes the source to emit three pulses."

                That is, the motion of the observer cannot change the wavelength ("the distances between subsequent pulses are not affected") and accordingly the speed of light as measured by the receiver is (4/3)c.

                Of all the physicists all over the world not one could think of a reason why this remarkable conclusion of Albert Einstein Institute should be discussed.

                Pentcho Valev