It is always possible that if someone manages to make string theory or a variant of SUSY that actually matches reality then a whole lot of things will fall into place when the dust settles. Quantum gravity has proved a very tough nut to crack. I am not holding my breath.
It has in always been that. Einstein originally introduced the term now know as "dark energy" to make his theory and the Einstein-Lemaitre universe model consistent with the then believed Steady State universe. The solutions otherwise had to expand or contract.
"Big bang" was a term used by Fred Hoyle to ridicule the new theory.
Inflation is another fixup although it makes predictions that are observed and helps arrange that space is very very flat and uniform.
Trouble is everything seems to work so well on all the scales we can study directly. It is only for galactic and galaxy clusters where the missing mass really shows up as a problem.
MOND is one such theory although again it smacks of adding a fudge factor to make theory fit with observations.
Reasonably complete description of CDM WIMPs, axions and MOND at
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I have a vague feeling that MOND has been almost ruled out now and that ordinary non-luminous matter has been ruled out by observation. Back in the 1980's you could hide missing mass as biros, chair legs and brown dwarfs but the latest telescopes are now so sensitive and over such a range of wavelengths that you can no longer hide ordinary matter.
Goldilocks sized black holes cannot be ruler out though.
In a sense what they have to look for is a failure of mass energy balance in a reaction since the WIMP will get away unseen.
Haha! In the 1980's. I maintained some parts of the read-out systems of the UA1 and UA2 experiments at CERN. You may remember that these experiments found the first W bosons and evidence for the existence of the Z boson. The running joke at the time was that if the mass-energy balance showed something missing, then congratulations, you had discovered a new particle.
The trouble was that the readout processors were so poorly designed that they would sometimes 'forget' to read out some sector of the detector, depending on temperature, activity elsewhere in the readout tree and many other vaguely defined issues. I still have a list of various types of misbehaviour with the associated causes somewhere.
I wasn't so convinced these bosons were actually real... OK, the LEP experiments used entirely different readout electronics and went on to detect copious amounts of W and Z, we are told.
Here's a philosophical question - is there a difference between a fudge factor added to an equation, or a fudge factor of "real" particles that we cannot interact with?
But yes, I am aware (meaning I have read a little about it, but the details are beyond me - I am at the "read an article in Scientific American or New Scientist" level here) of MOND as a hypothesis of this sort. MOND may not be the answer, but I feel that something along those lines would be more elegant than postulating new undetectable particles.
The real challenge with any of these hypotheses, such as MOND, string theory, or dark matter and/or dark energy, is finding experimental evidence for them. I think we will have to settle for "looks neat on paper, and matches current observations" - that's not enough for a good scientific theory, but it would be cheaper than building ever-bigger colliders and detectors.
A key point seems to be that for dark mass to explain the observed rotation of galaxies, the majority of the unseen mass has to be distributed roughly spherically (sort of like Saturn, with the observable galaxy as the rings of Saturn). Normal matter interacts in ways other than gravity, and this results in a flattening of a spinning disk (as we see in the shape of galaxies). Thus "dark" matter cannot interact with "ordinary" matter, or even other dark matter, except very weakly - by gravity, and perhaps other unknown very weak forces.
(I don't actually understand why this should be the case - as far as I knew, an evenly distributed spherical mass has exactly the same gravitational effect outside the sphere as a point-mass at the centre, while inside the sphere the gravitational effect decreases linearly from the "surface" towards 0 at the centre. I can't see how that explains why galaxies rotate faster than they should based on observable mass - but then, I am not taking relativity into account here.)
Tiny black holes, "lost" interstellar planets, cold gas clouds, and other non-luminous matter could account for some of the rotational anomaly, but not all of it. Thus I think they are part of the solution, but not the complete solution.
That's the idea. They hope to find a WIMP as the missing part after all the known pieces are accounted for.
The fact that relativity does not address the universe at small scales does not imply much about its accuracy at large scales. The issue at large scales is that we simply don't have enough data to understand what is really going on.
Not sure what all this is supposed to mean. I don't know for sure, but
at least as best it can be.
I think the real issue is that of the big bang and the fate of the universe. The big bang is a conclusion that is presented by the math of our current universe. The idea that our universe evolved from a point in time as a singularity is a matter of blindly accepting the result of an enormous extrapolation. If the physics change in a fundamental way (similar to the change from relativity) and the nature of our beginning changes as well.
In the end, I think we will never find an end to the unknown. Our observations will never be complete enough to fully understand the universe. A few hundred years from now we may realize that our belief in science is not much different from a belief in religion.
Why do you think that gravitons have a minimum force associated with them? Even if that is correct, that does not mean there is a limit to
interacting with a graviton given the larger area of a sphere with a larger distance. BTW, relativity doesn't predict gravitational forces.
My understanding is that string theory *does* match reality. The problem is that it also matches QM so that there is so far no experiment to distinguish the two.
I believe he called it the "cosmological constant" and considered it to be his biggest mistake. lol
I agree. But the fact that we have clear and concrete holes in relativity (at small scales) shows that it is incomplete - it should not be surprising if it also has holes at a large scale. (Obviously there is no implication that it /must/ have holes at large scales.)
It has been verified over a wide range of scales, and certainly it works for everyday usage (just as Newtonian mechanics works for most uses, and you only have to move to relativity for bigger or faster situations).
Basically, my argument is this:
Newtonian gravity and relativity explain the motion of stars and planets in out neighbourhood. But given the known matter in the galaxy and universe, gravity is too weak to explain the rotation of galaxies and too strong to explain the accelerating expansion of the universe.
There are three possible explanations for this:
There is a flaw in our observations or methods for calculating speeds and distances of distant objects.
There is vast amounts of unknown extra mass (dark matter) in galaxies, and even vaster amounts of unknown negative mass (dark energy) in the universe.
Newtonian gravity and relativity are good approximations up to stellar distances, but are less accurate over longer ranges.
I can't rule out any of these, but my feeling is that explanation 3 is the way forward. Dark matter, and especially dark energy, seem too contrived to me.
I don't think the big bang itself is a big leap of faith in the mathematics of the universe (as we currently know it) - we can see that the universe is expanding in all directions, and extrapolating that back to a point beginning is not at all unreasonable. Of course it may not be the correct extrapolation - perhaps the universe oscillates in size, and perhaps the physics used to determine the size and speed of distant galaxies is flawed. Certainly some aspects of modern big bang theories, such as inflation, can sound contrived - and thus should be treated with appropriate scepticism when considering new ideas and hypotheses. But the fundamental idea of the big bang sits strongly on theory and observation.
Science does not attempt to fully understand the universe, merely to push forward the boundaries of our knowledge and understanding. No scientist would claim that relativity is the "correct" model of the universe - merely that it is the best we have so far, and works well for a useful range. The phrase "belief in science" shows a misunderstanding of how science works, and what it means - with religion, you /believe/ you have /the/ answer, and resist all attempts to change or disprove it, while with science you /know/ you have only an approximate answer and welcome all attempts at disproving (and therefore improving) it.
If gravitons have a very small, but non-zero mass, then there would be limits to their range and possibly a minimum force.
But I don't have a reason for saying that gravitons /do/ have a minimal force (or a mass - or even that they really exist). I am saying that /if/ there are limits to their range in distance, or to their minimum force, then that could form the basis of an explanation for why gravity appears weaker than expected over cosmological distances - and I think that would be a clearer and neater explanation than "there is vast amounts of unknown negative mass pushing the universe apart". (And in case it is not clear, I am not saying that this must be the case simply /because/ it is clearer and neater - but that layers of complicated dark fudge factors sounds more and more like epicycles to me.)
I always found the HEP particle zoo somewhat worrying. I knew a few QCD theorists and at a handwaving level could just about follow their reasoning once upon a time. The experiments have got a lot more complicated since then. Needles in haystacks are easy by comparison!
If two different independent experiments see the same mass/energy resonance then the chances are it is real.
BTW wouldn't it be amusing if the missing CDM turned out to be bucky balls. Long suspected to be present now observationally confirmed:
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Unfortunately they need big stars at end of life to form. (so they are no help in the early universe)
Traditionally it happens just after some bigwig has made a major public pronouncement to the effect that physics will be entirely solved and completely understood in another twenty years.
One conjecture is that cunning demons are employed to look for novel experiments that will totally frustrate current established theories.
Certainly the theoreticians tend to react that way when their beautiful mathematics is ruined by an unexpected experimental result.
M-theory in 11 dimensions has so much symmetry that no-one really knows how to do reliable computations in it. An accessible review online at:
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Some of the best minds on the planet are struggling to come to terms with it. They might get somewhere eventually. Having 7 spatial dimensions so tightly curled up gives you a lot of wiggle room.
I am old fashioned and prefer my universe +++- rather than ++++++++++-
??? That is just an observable consequence of requiring the laws of physics to be the same for all observers in an inertial frame.
I believe the contraction was a patch up to explain the observations while preserving the current model at that time. It had no basis on theory other than that matter is made of charged particles. Very convenient that movement through the Aether would affect the scales being used to measure the movement so that it measured to be exactly zero.
In the same way dark "stuff" is likely a patch up to current theory.
For 3 to be considered the correct explanation, we would at least need to find a method to the inaccuracy involved. That is, can any other description of gravity and mass be applied sucessfully at the larger cosmological distances which provide a "better" solution? Then we can start to look for the basis of that "better" solution. Maybe we need to define what "better" even means in this context?
Yes, that is the part that is very unreasonable. It poses more questions than it answers.
I believe that trying to answer questions about the beginning and the end of the universe through physics is a category mistake. Science works through interpolation of data. These questions require extreme extrapolation and have a *very* low probability of being answered correctly. Potentially there are no possible answers to the questions. If so, why ask them at all? What do the questions even mean? Where is Deep Thought when you need it?
That is the point. We try to talk about the universe far beyond what we can reasonably surmise from our limited data, potentially beyond what we can even comprehend.
If gravitons have a non-zero mass, they would not travel at the speed of light. Or are you not referring to rest mass?
Yeah, so we need more data to create new theories which produce more questions requiring more data... not entirely unlike Zeno's paradox... or the expert's conundrum.
That is my point - the idea is to find a "better" (for some value of "better") set of equations than Newtonian gravity and relativity that fit the observed operation of the cosmos. As we have moved from older earth-centred ideas through Newton and then relativity, new models and equations have given more accurate representations of the cosmos. I can't help feeling that we have not reached the end, but that there is scope for further steps.
Of course, since I have no idea what these further steps might be, I cannot say more than that.
OK, extrapolating back /towards/ a point is not unreasonable. Actually hitting the point is a bigger step. And yes, it poses many new questions - but that's common in science.
Science works by extrapolation as much as by interpolation. One of the key features of a scientific theory is that it makes predictions that can be verified - that is extrapolation.
I can agree that questioning the very ends of time and the universe is a special kind of science - it involves working from very limited data, and it is typically impossible to perform experiments or otherwise verify hypotheses. But science and physics is the best tool we have for asking and attempting to answer these questions, even though they may never give complete answers (or even complete questions :-)
We are /human/ - we've always asked that sort of question. The difference now is that we try to do it by looking at microwave background radiation, slamming particles together in accelerators, and writing complicated maths on blackboards (or inside Hawkin's head). Previously we answered them with stories such as Odin slaying the first giant and making mountains out of its bones.
No, you are correct - with non-zero rest mass they would not travel at the speed of light. Do you know of any confirmation that gravity /does/ act at the speed of light? (This is all pure speculation on my part.)
That is kinda the point. Just as my expectation that we are approaching a "new" discovery equivalent to relativity is just an expectation, your "idea" is nothing more than that we nothing to support that it will happen. There is nothing to suggest the observations of the cosmos will impact the existing theories of gravity.
Extrapolation is just that, drawing conclusions far removed from the data you posses. I can extrapolate the flight of an airplane based on the last 30 minutes of it's flight, but that won't tell me where it took off from since the flight has been altered many times since it was airborne.
Rather than look at where the data points, look at how this point has moved over the ages. There is no reason to believe that our current idea of the origin of the universe is any more accurate than it was 100 years ago. We may have more data, but we are projecting even further backwards.
No, that *can* be extrapolation, but most verifiable predictions are interpolations. If a prediction can't be verified, it is of little value in supporting a theory.
Even that is an assumption. I think I have said that much of what we look to science for answers are simply not in that domain. The origin of the universe is likely a question that can never be answered by science. Asking the question in science is a category error. We have a model that says the universe started from a singularity... which we know nothing about. Clearly this is not a useful answer to the question and will likely to be shown wrong at some point. Then that new result will be shown wrong... etc. without ever finding an answer that is any more useful.
Which of these answers have proven to be useful?
We can't prove that light travels at the speed of light as there is always experimental error. Other than experimental error, aren't our observations always in accord with the existing theories of gravity?
Normally new theories have some particular observational basis.
That's also true at very small scales and near black holes. The LHC is ge tting us more, and better data than we've ever had before, but not nearly e nough. As for black holes, well, they're difficult to work with close up an d personal...
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That's my understanding as well. What hasn't been verified very well is t he strength of the gravitational constant despite more than two centuries o f increasingly precise measurements- the value doesn't seem to want to hold still.
It's the result of seeing an increasing redshift correlated with increasi ng distance. Two reasonable interpretations- an expanding universe or "tire d light". Since we do not see the scattering inherent in tired light theori es, that leaves the expanding universe.
I disagree. Religion is about belief despite a lack of evidence or in the face of counter-evidence, science is about evidence trumping belief.
Photons are basically ordered fluctuations in the electromagnetic field. QM predicts, and we have seen, that that field has random fluctuations ever ywhere. Get far enough from a source of ordered fluctuations (photons from an antenna frex) and the ordered fluctuations are swamped out by the random ones.
The same should apply to (so far) hypothetical gravitons.
However, despite some serious effort, gravitons have not yet been detecte d directly. Suppose we never do manage to detect them?
Small black holes are not so hard to work with. If they are made with a charge they can be suspended so as not to touch anything. Make them too small and they just go poof. Make them a little bigger and they leak away a bit more slowly.
Or something else...
You don't understand the basis of science. All science and especially math is founded on a small set of assumptions. We continue to build on that and as long as we don't find contradictions we are good. But we ignore many, many small issues. The first time I saw that was in a course where they looked at science with a critical eye. For example, we looked at the notebook entries for the Millikan oil drop experiment. Millikan is famous for being an expert experimentalist. He had some "outlier" data which he discarded. We routinely discard data that we feel is outside of our expected range assuming it is "experimental error" and accept that as part of the "process". Science is full of "issues" that we gloss over because it is convenient.
Math is even worse. There is no starting point for math unless you start with an assumption. Pick one of many. Then build on that. But it is built on an assumption so it can never be said to be absolute.
Then there is always the issues of interpreting your data. Collecting data and drawing conclusions from it is inductive reasoning, creating rules from observations. Rules that can *never* be proven right by induction, only proven wrong.
Religion is what you believe. Science is what you believe.
What does that have to do with the statement I was replying to?
"Once the force predicted by relativity is too small for a single quantum of gravity, it simply cannot be mediated at all."
I won't be around to see "never". But this is a limitation of science. Observations are limited and so the rules we construct are always limited. Science is only applicable to the repeatable. Life is not completely about the repeatable nor is the universe, especially the big bang.
Yes, we are saying the same thing, just with marginally different wording.
No, extrapolation is not drawing conclusions /far/ removed from the data you possess. It is about drawing conclusions from data /somewhat/ removed from the data you possess. Based on the 30 minutes flight data, you predict the next 30 minutes - and based on what you know of aeroplane flights and what you have seen in the 30 minutes you know about, you can estimate the uncertainty in your predictions. If you are reasonably sure of your predictions, as you probably are for the next 30 minutes, then you have extrapolations. If you are not sure, then you have speculations - and if you are very unsure, you have hypotheses or wild guesses.
Take three bricks of different sizes, hold them above your feet, let them go, and observe their behaviour. Take a fourth brick, bigger than the rest. If you feel confident that it will also fall like the others, and will hurt your toes even more, then you have successfully extrapolated from the known data - and that is a key part of science.
There is plenty of reason to suggest that our current ideas are better than our ideas 100 years ago. For one thing, we know now that all the other galaxies in the observable universe are moving away from us, with a speed approximately proportional to their distance from us. We have vastly greater knowledge of how the universe has developed in the past
13.5 billion years or so.
The very beginnings of the universe are still a matter of speculation, but current theory gives reasonable explanations for the progress between a tiny fraction of a second after the big bang, until current time.
That's basically true, although I don't know if it's fair to say /most/ verifiable predictions are interpolations (nor do I know if it is unfair). Depending on the type of data involved, it's not always clear if predictions are interpolations or extrapolations. But there is no doubt that extrapolation is key to science - there would be no science without it.
That is your opinion, and that's fair enough. Some people think that science is our best tool for such questions and answers, others think that religion is the right tool, and others think something else (such as that there is no current tool, or simply that there is no point in asking such questions).
There are no facts on this one, merely opinions, and it's fine to differ on opinions.
Science works by posing theories that fit observations, then gradually improving these by showing that the previous theories were wrong, or at least inaccurate. (But as noted above, if you don't believe science can ever answer questions about the start of the universe, then that's a perfectly valid and rational standpoint, so I won't argue against it.)
Well, Norse mythology has given us names for the days of the week, and that's useful. The search for big questions and big answers in physics has led to new technology, new science, and inspired scientists and engineers, so that's useful too. The origin of the universe doesn't make a difference to daily life - it's the side effects that are important and useful.
Our observations are in accord with the existing theories of gravity - /if/ you accept the hypotheses of dark matter and dark energy. If you put these hypotheses aside, then our large scale observations are /not/ in accord with existing theories of gravity (or there is something else going on that we haven't thought of yet). That's the whole point.
That's the theory, anyway - it has not be demonstrated in practice!
Making charged black holes would be a serious challenge - you would have to create it from or feed in electrons or protons to give it a charge. But the electrical repulsive force would far exceed the gravitational attraction (small black holes have small gravity), and thus require enormous forces and absurd accuracy to force more charged particles into a charged small black hole.
Indeed. We can't rule out anything here.
The assumptions are well-known, and clearly stated. Much of maths is built on the Peano axioms, for example, but sometimes different axiom systems are used or one or two axioms are added or removed. In both maths and science, we start somewhat in the middle and push out - deriving new ideas and theories from existing ones, and trying to learn lower-level, more fundamental bases. For maths, the work on establishing the fundaments is mostly in place - the Peano axioms or their equivalents are necessary and sufficient for basic arithmetic to work.
Neither maths nor science in general builds on a /belief/ in these low-level axioms - they build on the /assumption/ of those axioms and low-level building blocks. If our understanding of the low-level stuff changes, as has happened many times in physics, that may or may not lead to changes higher up. But that's okay - science works when something is proved wrong. This process means that a chemist can assume the workings of atoms and use that to do more chemistry. And a civil engineer can use that chemistry to build bridges from cement. Meanwhile, the particle physicist is challenging the way atoms are build. Every scientist assumes that the current models of most aspects of the universe are pretty accurate, while working on their own particular part
- with the goal being to find new models or disprove old ones.
Regarding Millikan's oil drop experiment, I only know what is written in the Wikipedia page which suggests that the skipped data was perhaps discarded for good reason, and even if included it only affected the statistical error margin a little.
But of course scientists are still humans, and may make mistakes or intentionally "fiddle" things. That is one of the reasons science insists on independent repetition of experimental evidence.
And yes, scientists always try to simplify things and in reality there are always additional effects. That is nothing new.
Yes, maths is built up from axioms. Again, this is nothing new, and should be no surprise to anyone interested in maths or science (Euclid worked from axioms in ancient Greece).
A key point about axioms, however, is that they are (except when doing particularly obscure mathematical logic) clear and "obviously correct". Euclid used axioms such as "if you have two separate points on a plane, you can draw a line between them". If you don't feel that this sort of thing is a reasonable basis to work from, then you quickly end up with "we can't really know /anything/ for sure" thoughts - which are true, but get us nowhere.
Correct. That's why science never claims to know things absolutely, but only provides the best known models and theories until those get disproved.
No - religion is about believing despite lack of evidence, and in the face of contrary evidence. Science is about temporarily accepting theories based on known evidence, and rejecting them when giving contrary evidence. They are almost exact opposites.
I gather experimental apparatus needed to have a significant chance of detecting gravitons directly would involve things like galactic black holes, so I doubt that we will see them in the near future.
The origin of the universe is not "somewhat" removed from our data.
Until we figure out why we so badly misunderstood the existing anomalies.
You only need to give it a bit of thought. Science deals with the things that can be observed and repeated. The "origin of the universe" is so far removed from this domain that it is unreasonable to expect to ever find a valid answer. Much like the joke about the drunk who lost his keys in his front yard, but is looking for them under the street lamp... because the light is so much better. We look to science for answers to questions it can't answer because we think science gives us better light.
So we know *something* is wrong. How does that equate to gravitons having a maximum effective distance?
They jam charged particles together all the time. Ever hear of the LHC?
Yes, these assumptions are required to have the rest of math work.
Distinction without a purpose.
Your construct has no meaning in this context. Bees and ants create structures without science or math.... so?
Yes, the "obviously" correct aspect is what I'm talking about. It is "obvious" that they work where they work. In the end the entirety of math and science is a framework built on these assumptions that ultimately can lead to falsehoods. It is *not* absolute in any way. When you talk about verification, you mean bringing predictions into the domain of interpolation rather than extrapolation. We can only ever do that in a very limited subset when dealing with the cosmos. So our theories have huge ranges over which they can not be verified.
You are starting to catch on now. Science *can't* tell us about things like the origin of the universe because that is too outside of what can be verified. It is at the end of the whip being cracked this way and that as the rest of the whip is thrashed about by the scientific process.
You simply don't consider anything other than "science" as evidence. Science only considers "scientific" evidence. People consider much more. Remember that science can only deal with that which is repeatable.
The origin of the universe is more "speculation" than "extrapolation" (using my new, imprecise and non-scientific terms). Some science is done with in familiar situations and is "somewhat removed" from current data. And some science is done with extreme situations and a good deal less certainty.
Maybe we will - and again, proving old theories wrong and coming up with new and better ones is what science is all about. The science of the big bang (which I don't claim to understand) appears to be pretty solid, so it will take a lot to topple it - but it is certainly a possibility.
There is a good deal about the state of the early universe that can be observed and repeated to some degree, albeit on a smaller scale. Particle colliders and other high-energy experiments can replicate some of the states of matter from the early times and measure some of the effects. And simulations can let scientists play out the effects of models and gauge their accuracy. Obviously it's a completely different think from repeating an oil-drop experiment in two or three different labs, but it is still science.
As I said before, you have your opinion about what science can and cannot answer. But of curiosity, if not science, then what tools would you use (or hope that others would use) to answer these sorts of questions?
It does not "equate" to gravitons having a maximum effective distance, and I never suggested that it did. That is nothing more than a wild idea from my side - based purely on the idea that /if/ gravitons have a maximum effective distance, then gravity would appear weaker on an intergalactic scale without needing to introduce "dark energy" or a "cosmological constant" in order to fit the observed acceleration of the expansion of the universe.
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