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    I 7 exoplanets around TRAPPIST-1

    The Trappist discovery has caught the attention of the world outside Physics Forums to an extent which could justify calling this discovery bizarre. How justified is such a label? Enough to mention a bizarre possibility? One which in another context would surprise few -- namely that maybe...
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    A Gravity as a non renormalizable theory

    Could you give an observed example of such a system? It is an example beyond the scope of any kind of physics.
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    A Where are the Higgs particles?

    I've been reading Jim Baggott's book "Higgs -- The Invention and Discovery of the 'God Particle' "and have a rather elementary question, easily answered, I'm sure, by folk that contribute to this forum: is the Higgs only associated with the inner machinations of other 'elementary' particles, or...
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    I Inflation and the false vacuum

    Fields are mathematical constructs, useful in physics, that assign scalar, vector, tensor quantities to each and every point in spacetime. The convention has developed in quantum physics of ending the names of the quanta of fields with "-on"; for example photon, electron and so also inflaton...
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    Hype about gravitational waves

    There seems to be considerable interest in the recent detection of gravitational waves. For the physics community this interest is fully justified. But in the popular press it seems to me to be reaching unjustified and perhaps harmful levels. When one reads overblown hype like: " A giant...
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    Is String Theory Testable?

    Quantum Field Theory agrees with observation to an extent not quantitatively matched by any other human mental construct. Doesn't this answer your question in the affirmative, Haushofer?
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    POLL: How do you think of the Hubble rate?

    Thanks especially for post #5. And Schiller was a contemporary of one of my great-something grandfathers, Lessing; so I prefer to think of cosmic expansion like matter in rising dough, rather than quantitatively, and vote #6.
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    Equivalence of inertial and gravitational mass

    Thanks for your reply #15, ohwilleke. You wrote : "The difference between mass and mass-energy, however, is not just semantics. It is a fundamental concept that you need to understand the question you are asking in the first place in a way that has a meaningful answer." Yes, mass is an...
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    Equivalence of inertial and gravitational mass

    Thanks, Haushofer. It's time that we got away from semantics. I would still like to know whether the photons that comprise a beam of radiation attract one another, or not, and to have the reasons for the reply, whatever it is, spelled out.
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    Equivalence of inertial and gravitational mass

    I seem to have worded my question in an irritating way. But I take issue with the statement in post #6 that photons don't have 'gravitational' mass. They don't have 'rest' mass, but they do gravitate: their geodesic trajectories through spacetime are indeed affected by matter concentrations...
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    Equivalence of inertial and gravitational mass

    Still puzzling. Consider photons -- entities without rest mass that are nevertheless endowed with energy E = just because they wobble in time. And energy is mass, given by m = E/c^2. I guess this mass should be labelled 'gravitational' because photons gravitate and light is known to be...
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    Equivalence of inertial and gravitational mass

    Is there any credible hard evidence that this equivalence extends to all moving bodies? We accept on good grounds that the apparent mass of moving objects is enhanced by motion, to a measurable degree that increases indefinitely as observed speeds of relative motion approach c. Likewise...
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    Why is the Universe (nearly) flat?

    strikes me as something not answerable by Physics, which doesn't answer "why" questions --it tells only "how" stuff came to be; here via the agency of a scalar inflaton field. But I'd like to know whether such a field is a logically inevitable ingredient of any extensive universe's initial...
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    Smolin: Extending dualities to trialities (deepens dynamics)

    Please, somebody, translate for me what seems to me to be an illiterate phrase in an interesting article.
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    Faster than light - time

    [ Yes --- it's accepted that one can't send information via tachyons (faster than light), if indeed such things 'exist'. But there are humbler physical entities that seem to me to be able to outrun the waves that carry them. Here's my story: I live facing west, across an ocean beach. Early...
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    Information as the key underlying physical principle

    I vaguely remember that NASA folk have already acted on this possibility. The human artefact that is now remotest from planet Earth is, I think, an early space probe (Pioneer?) that is now travelling away, far beyond the solar system. It carries a plaque with an engraved message to any alien...
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    Information as the key underlying physical principle

    Again, what we actually are (walking, talking, and now writing primates) is key here. We describe what matters to us because we can. In your example the ancient brute created a four-rock pattern which you so described with the help of the extant language of arithmetic; an ancient abstract ...
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    Information as the key underlying physical principle

    I'm afraid I agree with the ancient pebble pusher. Even at the risk of being thought silly , I resist the proposition that two and two make four can be characterised as some sort of eternal truth, and prefer to think of calculus as an evolved and heroic human invention; certainly not as a...
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    Information as the key underlying physical principle

    I suspect that there is an elephant in this particular room, namely the distinction between what we are and what we do. Just as an elephant is an animal, so are we. And, although elephants do communicate well enough for elephant purposes, we excel in this respect -- as in this interesting...
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    A festive analogy for interpreting quantum mechanics

    Neither am I! A fly in the ointment with this approach, one that worries me severely, is the scaling of quantum phenomena by Planck's constant. I have no idea why h has the numerical value it does -- perhaps there's a a reason for this, rather than just happenstance. Endless mysteries. Have...
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    A festive analogy for interpreting quantum mechanics

    While browsing this festive morning I came across Peter Woit's "(his Oct. 3rd 2011 'Not Even Wrong') statements that: "the fundamental problem of the interpretation of quantum mechanics (is): why don't we see superpositions " and that: "the confusing question is classical behaviour...
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    Does LQG Do Nothing Cool Even If It Is Right?

    Thanks, Marcus. Yes, Faraday invented the field concept, which gains huge credibility when one looks at patterns of iron filings near a magnet and leads on later to Maxwell's quantitative description of interactions between charges in terms of dynamic E and B (or is it H?) fields. Fields...
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    Does LQG Do Nothing Cool Even If It Is Right?

    Interesting remark: My grip on physics history is shaky! Which early fields? Are you perhaps thinking of old vortex-theory days?
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    Does LQG Do Nothing Cool Even If It Is Right?

    The central thesis of LQG, namely that space is discrete rather than continuous, and the question: how many angels can dance on the head of a pin? both seem to me to skate rather close to the thin ice of sophistry. If space is intrinsically discrete, then I’d expect measurements of localised...
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    How time starts in LQG with onset of Lorentzian phase

    Mielczarek, Linsefors and Barrau , as far as I can dimly understand, are proposing that the history of the universe includes an 'episode' timelessly called 'a state of silence' in which the time dimension, the fourth in our current Lorentzian ensemble of dimensions, became added to a...
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    Does LQG Do Nothing Cool Even If It Is Right?

    It sounds to me as if some sort of wheel is waiting to be to be re-invented here, as the attention of particle-physicists seems now to be turning towards patterns of distortion in spacetime, with localised curvature, and variations in curvature, somehow endowing mass/energy with a...
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    Does LQG Do Nothing Cool Even If It Is Right?

    Barrau and Grain wrote (on Page 4 of their paper, see Post # 1 ) "In bouncing cosmologies, either from the loop approach or any other, the question of anisotropies is very important for a clear reason: the shear term varies as a^(-6) where a is the "mean" scale factor of the Universe . When...
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    QFT and String Theory

    " Going from standing waves and instatons of a field to particles is pretty trival and virtually indistinguishable." Sounds authoritative. But indistinguishable from what?
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    QFT and String Theory

    "It seems that String Theory says that the "particle first" approach to QFT is better because it is closer to the actual truth: particles *are* fundamental, they're just not point-like. " The 'actual truth' is, as I see it, coloured by one's perspective. And perspective depends on life's long...