joigus

There is absolutely no problem in extending GR to include anti-orthocronous Lorentz transformations. GR is invariant under the whole group, not only the connected subgroup. It's the standard model that's in conflict with T, P, CP, not GR.

All words and no maths make Jack's a dull toy

Yes, @Eise. You've just kind of voiced my concerns here. I don't know in detail about those critical voices, but I'm sure they must sound something like this: So we have to accept that, even though everything in the universe thermalises very quickly, somehow this information, which is dynamical in nature, must be protected from thermalising so that one day in a laboratory in, say, Vienna, a physicists chooses a polarisation direction and the universe conjures up that information? While not impossible, it rings totally wrong. It goes against everything else we know about entropy, the arrow of time, etc. Degrees of freedom thermalise, mix, get blurred out with time. What magical DoF's are these?

OK. So here's what my friend tells me. Keep in mind it's not a technical explanation..., <Translation> Yes, sure. They do it with their uncertainties. They actually see how electrons go from one atom to another to form a molecule, as I understand. It's kind of my topic. Well.., the attosecond pulses themselves, not their utility concerning interactions with matter and watching electrons. </end of translation> Maybe the "see" and "watch" had better be put in quotation marks, or something like that.

Thanks, Eise. I'll have to look into it more deeply, but for the time beeing it checks with my understanding that superdeterminism is similar to the observation that bipartite, tripartite etc entangled states are correlated (strangely, non-realistically, unintuitively, so on) from the beginning. It's that statement but on steroids. Namely: Everything is entangled from the very beginning (or perhaps non-beginning, as the Mahayana teachers say) of time. Something like that, but I would like to read more about it.

I'm guessing that's a piece of journalistic lingo. Sorry, it's not my claim, it's my friend's. He seems to have picked it up from the newsreel. It's not like he wrote it trying to be rigorous. It does sound akin to some kind of stroboscopic view, like @geordief suggests.

I'm asking my friend, see what he tells me. He's a university professor and a researcher in non-linear optics, so he should know... BTW, @geordief, a clarification on what I meant before: A femtosecond would be 10-15 seconds. People in the field already call a 0.999 fs short pulse an "attosecond", even though it's almost 1000 attos (a femto). In the meantime, looking up: https://en.wikipedia.org/wiki/Ultrashort_pulse You find, Which, I think, must have the answer to our question.

I've just received an email from a friend who's working on the theoretical part of the same stuff these people are doing. These are the people who've made attosecond-short (10-18 seconds) pulses of light a reality. The record is in 25 attoseconds. People already call "attoseconds" a fraction-of-a-femtosecond-short pulse of light. The one 25-attoseconds-short already allows you to see electrons moving. Amazing.

Yes, they'll probably still be here after we're long gone.

Not true. Not accurately enough for certain cases (perihelion of Mercury) and for certain purposes (high precision location in GPS systems). In those cases, it's general relativity that does the job. And don't forget that GR reduces to special relativity at every point. There are very many ways in which we know SR to be right.

These are actually the significant ones, the ones that are dimensionless. Including, of course, the Planck scale.

Sorry, I meant theologians. This reminds me of comments made by @Eise on the late thread about local realism in the sense that we've reached a point where nothing but endless model-building, extrapolation and back-consistency checks --so to speak-- is possible.

I'm not aware of having pointed out that the idea of a multiverse is diferent from a multiverse itself. But it's obvious, isn't it? Same goes for the idea of anything compared to the thing itself. Thinking otherwise is known in philosophy as the use-mention error, which consists in ignoring the use-mention distinction. Theologists do it all the time. History of God = History of the concept of God. Not the same thing!! I'm sure Daniel Dennett has dealt with this question somewhere. The idea of a multiverse is what our minds handle when we speculate wich such possibility. The multiverse would be what we would experience if we could travel through time and space quite freely and experience those domains directly, which we never will. I don't think we will.

Exactly. I didn't want to open that can of worms, but I agree. How can you get any picture at all of a sample space (and its odds) that you've never probed, and never will?

I would rephrase "worlds apart in many senses". Maybe "in almost every sense conceivable" is too much. My point is: It took about 20% of the age of the Earth to get to something like eukaryotes that was sure-footed enough in evolutionary terms when prokaryots already had more than a foothold. Which must mean higher-organization is not easy to come by.

Don't forget prokaryotes and eukaryotes are worlds apart in almost every sense conceivable. If I had to bet, I'd say life that's similar in organizational level to prokaryotes is relatively common in the universe. But eukaryotes are a completely different kettle of fish, my friend. It took many eons, ( a whole boring billion years at least) for them to appear when Earth already looked like there was gonna be nothing but bacteria and archaea forever and a day. This concept of deep time takes a while of ordinary human thinking time to sink in. The most likely thing out there is some kind of mush, just because the most likely thing around here is some kind of mush. The world we see now is anecdotal in comparison.

It's not that fine-tuning suggests a multiverse, I think. Rather, the idea of a multiverse (with different domains having different values of the physical constants) makes whatever value for the constants inescapable for some part of the multiverse where there is intelligent life, therefore supressing the need for an "outside" contrivance (creator). There are other games in town. Eg, Smolin et al.'s idea of cosmic selection, Tim Palmer et al.'s idea of universal constants as coming from attractors of some chaotic regime, etc. I'm not going to watch the video, sorry.

I was gonna say something similar to what Swanson said. I suspect subtlety is in the word "find." If "find" = "identify unmistakable telltale signature of", then I think I understand what those scientists are saying, and I wouldn't be totally shocked.

Here I should've said the Levi-Civita connection, sorry. Anyway, even the manifold connection can be introduced independently from the metric.

In case anyone's interested... In addition to baryon number non-conservation, one would need T (=CP) violation, plus C violation alone, plus a universe out of equilibrium --if I remember correctly-- for baryon asymmetry. As we already know of C and CP violation, T would be automatically satisfied if CPT holds, which we believe to be the case. https://en.wikipedia.org/wiki/Baryogenesis#GUT_Baryogenesis_under_Sakharov_conditions

Exactly. Subtract 8 from 24 24-8=16 (waking hours) Multiply by 3600 (seconds per hour) 16*3600=57600 Divide by 10000 (ads per day) 57600/10000=5.76 seconds per day available to see an ad with the minimum estimate of 4000 ads you get 14.4 seconds. Still not very believable. There wouldn't be time for anything else. Your screen or interface might "see" those ads. You don't. That's why they hire so-called attention-engineers.

Great summary. I agree with Genady and Markus. Connections are quite independent of metric in general. It's one of the hallmarks of Einstein's GR that the connection is a metric one. Thereby the words "metric connection". Rods haven't been a standard for quite a while. A gauge fibre bundle is an example of a metric-less connection. The gauge field A provides the parallel transport along the manifold, while the gradient of A gives you the parallel tranport on the fibres \( \Psi \), the whole structure is (locally) a product MxF (M=manifold, F=fibres), but with no metric for the \( \Psi \)'s. Sometimes I have a problem understanding what the OP sets out to do. This is one of those times. Before one starts thinking about physics, one should get a clear picture of what needs to be solved. Going back to metric connections in order to try to solve a problem GR doesn't have doesn't look promising. Things that are considered solved are considered solved for a reason or, should I say, for a bundle* of reasons. *

The golden ratio is the positive root of x2=x+1 That is (1+sqrt(5))/2 https://en.wikipedia.org/wiki/Golden_ratio In a certain sense, it is the most irrational number, meaning that its continued-fraction approximations are as bad as can be. The letter phi is used for many things. It would be futile to try to give a complete list.

I totally agree with @Genady too. We seem to be fo the same mind in this respect, or very similar. The way Kant analised Nature and science, and epistemology, blew my mind when I was a teenager. Didn't follow him quite equally well when he spoke about other things, moral in particular, or "practical reason." In fact, I see many clues that the world we see and measure could be but a projection from some more "fundamental" level, perhaps involving things other than geometry. Watching for clues from pure mathematics could not be entirely misguided.

Time is a scalar under spatial rotations. Time is not a scalar under changes of reference frame that involve a speed. Also, things that change sign under certain transformations (spatial inversions) are scalars for everything else (every other transformation of coordinates). Those are called pseudoscalars. An example is the projection of an angular velocity on a fixed vector of space. Another example is the wave funtion of a meson. Etc. Which one do you mean? Also, a vector and a dimension are different things, as you've been told. Etc.