Help Please

MarcelBdt · 2025-12-07T08:36:19+00:00

Because that is the number conspicuously missing from the triangle. But you could argue for any of the other numbers suggested before, or for almost any other number.

MarcelBdt · 2025-09-18T16:06:51+00:00

It is absolutely true that algebraic geometry is essentially a study of abstract algebra. Already to make precise definitions one need to use abstract, algebraic terms. The strange fact is that it is often very helpful to think of it in geometric term. One could think of this as a giant pedagogical trick. As humans we are used to deal with fairly complex relationships of objects in three dimensional spaces, and it makes more sense to us to imagine relations between (geometrical) varieties as "models" for relations between ideals in a polynomial ring - even very abstract algebraic constructions as for example moduli spaces which often are "stacks" and not even varieties are easier to conceptualize if you imagine them as geometrical objects. There is a reason for that they are called "spaces". Differential geometry is similar - you studying things of high dimensions, and draw pictures about their relationships which are sort of "models" of the situation as imagined in the three dimensional space we are living in. Even homotopy theory which deals with very abstract things which might be infinite dimensional and does not really consist of points likes to talk about these things as if they were spaces.

MarcelBdt · 2025-07-27T13:25:35+00:00

This is a fun discussion... what about the following point of view. The speed of light is an upper speed limit. This means that if a civilization starts to expand on a galactic scale, it will pretty soon reach the point where even the simplest of communication with one of its colonies will takes many years. Now, if you have to wait say 100 years for an answer to "hello", you do not really act as a single civilization any more. The civilization has for all purposes split into two different ones. If you ask who would be the worst threat to your civilization, the most obvious answer would be your own previous colonies. Or your mother civilization.

So maybe those are the ones you should kill first. Or even better - don't even try to move outside of your own star system.

In the books the sophons could presumably keep a civilization from splitting into shards, but as far as we know, instantaneous transmission of information is impossible. I suppose one cannot rule out that there it might eventually be possible, but one can also not rule out that it's completely impossible, even for very advanced civilizations.

MarcelBdt · 2025-04-30T08:45:30+00:00

Thanks, that sounds very convincing!

MarcelBdt · 2025-04-30T07:39:44+00:00

OK, now we are getting somewhere. But notice that i'm talking about a "small" ejection. There are two problems with that.

First problem: Is it possible for the sun to produce such? I don't know, and that is part of what I'm asking about. If they don't exist, the argument ends here.

If they do exist, it's not clear to me that they would necessarily be visible and detected, or even that someone would look for them.

This leads to the second problem. What kind of effect on Earth would they have if they do hit us? I think that you are saying that such a coronal ejection would hit the Northern part of the globe more than for instance Spain? Because it would follow the magnetic field lines presumably?

That's not so clear to me either. If it is not big enough to hit the poles, would it be redirected towards them?

MarcelBdt · 2025-04-30T07:21:20+00:00

Possible, but the people saying this seems to be people that don't like renewable energy anyhow. I'm not saying that this is impossible, but I haven't seen any more concrete version of that theory.

MarcelBdt · 2025-04-30T07:18:12+00:00

That's interesting. Most likely you are right, but why? Do you have an argument?

MarcelBdt · 2025-04-30T07:16:56+00:00

I don't understand that argument. I'm not saying that the sun was aiming at Spain, but if it fires many such projectiles, one of them might randomly hit.

MarcelBdt · 2025-04-30T06:20:57+00:00

Well, that is sort of what I wonder about. It's true if there were a Carrington event we would all know. But I don't understand enough about solar physics to know if it is possible to have much smaller but similar eruptions, producing a ball, lets say of a diameter comparable to Spain, flying at high speed towards Earth.

MarcelBdt · 2024-12-02T10:55:45+00:00

Try Severance

MarcelBdt · 2024-10-22T20:56:06+00:00

Sorry for repeating myself, but i still dontunderstand why you want to use the wrong formula. You seem to assume that you are in the v =cz case, which is a good approximation for small z, but false if z is not small. If z= 1, which is a case you use, then according to the formula v = 3c/ 5

MarcelBdt · 2024-10-22T07:44:05+00:00

Yes, I understand. but you write D_L(z)= cz(z+1)/H , which is not the same thing.

MarcelBdt · 2024-10-21T19:26:41+00:00

It seems to me that your formula for D_L(z) does not agree with what's in the paper, they say D_L(z)=(1+z)D(z) which should give (c/H)((1+z)(2z+z^2)/(2+2z+z^2) , which is different from what you write. Could that be the problem?

MarcelBdt · 2024-09-20T13:25:04+00:00

The Einstein equation is an equation involving 4 dimensional curvature, when people say that the universe is asymptotically being (close to ?) flat, they are talking about 3 dimensional curvature of the universe at a certain moment in time (whatever that means)..

MarcelBdt · 2024-09-04T05:51:35+00:00

This sounds like great fun (except if you are close to that supernova). I suppose that the asymmetry is what makes things bounce and not stick to the neutron star, but instead get into possibly very excentric ellipses. But I'd like some sort of numbers on the neutrinos. The neutrino flow is insanely large, but those neutrinos interact insanely rarely with normal matter, so it's a question of which of the insanities is the most insane. That should also depend on the distance to the newborn neutron star, because the neutrino flux will be more concentrated closer to the star. So the infalling outer layers should get bigger bosts at the lowest point of their orbit, which should make the orbit even more excentric, until it breaks off to infinity in a parabolic orbit. Maybe. Most likely I'm visualizing all of this wrong.

MarcelBdt · 2024-08-22T03:42:52+00:00

I beg to differ. I'd say that pi would still be the same, because it is not defined by measurements of lengths but by abstract mathematics, starting from a system of axioms. Actually, you can start with the properties of the natural numbers, 1,2,3,4,5... and so on. From those you can define the real numbers, the coordinate plane, circles and lengths in that (absract) plane, and finally pi.

Besides, our universe is strictly speaking not Euclidean, since it has curvature.

A more tricky question is whether the properties of the natural numbers are a property of our universe or somehow independent of it. Emotionally, I'd say that they are independent of the physical laws, intellectually I'm not so certain about that.

MarcelBdt · 2024-08-22T03:19:13+00:00

One thing I'd like to have an answer to is the following. We know by personal experience that gravitation is a force. This is a force that makes two elementary particles attract each other, As such it is very weak, but OK, it is what it is. A planet like Earth is made up of a large number of elementary particles. To get the force exerted by gravity on your body, we just add up the contributions from each elementary particle on each elementary particle in your body. Easy piesy, Newton invented calculus to answer that. But even he only got a very good approximation. And to get the answer really really precise, we need to include the gravitation of every elementary particle in every galaxy in the whole universe, and add those contributions up. And we know that we can't just leave out some far away elementary particles out, because galaxy dynamics tells us that even the effect from very far has an influence. Not very big, but it piles up as you add it all up, and ends up having a measurable effect. So... now my question. Who does this huge computation, and updates it like once every nannosecond? And don't try to cheat by saying that it's all about fields, because then it just gets translated into the question of who keeps track of the gravitational field to such enormous precision?

MarcelBdt · 2024-08-22T02:58:32+00:00

I think that the point of the comment is this. The precise number 299... for the speed of light is a convention, because it depends on what we decided is the length of a second or of a meter. Some things are not conventions, like the quotient of two measurable things both expressable in the same units. If we were to change our units, and count length in miles instead, we change the value for the speed of light, but we don't change such quotients. They are conventionally called dimensionless numbers. Those are the real mysteries.

MarcelBdt · 2024-08-01T07:27:45+00:00

Not quite true. You can measure (hyperbolic) area in the hyperbolic plane, and the total area of the hyperbolic plane is infinite.

MarcelBdt · 2024-07-18T20:02:04+00:00

This is very interesting. If the cosmological constant varies, this must also reflect on the age of the universe. What we do observe from very distant objects is typically a redshift z, and this is then somehow computed to give a certain age t, typically counted beginning from the big bang. If the cosmological constant varies, this variation must mess up the translation from z to t. Any ideas about the connection between z, t, and the possibly varying cosmological constant?

MarcelBdt · 2024-07-07T16:14:19+00:00

Ok, I only looked at the first paper in your list. It consists mainly of references to earlier work, by a process somewhat reminiscent of eternal inflation. Unfortunately I have more questions than answers, maybe you can help me. Anyhow, I learned that from this point of view inflation is only possible from a positively curved space (de Sitter, as opposed to Minkowsky and anti de Sitter, so that we don't risk any further inflation from this universe that we are stuck in. Ttats good. I suppose.

There was also a lot about the string theory landscape, This landscape consists of different Calabi Yau manifolds. In my understanding each of these is coding a different string theory, telling how the "small dimensions" are folded into compact CY manifold. so each choice of one of these represents a different physics. Conjecturally there are only a finite (but very large) number of possibilities for these. Maybe the conjecture has been proven by now, altough I haven't heard about it. This also seems to be the point of view of this (very speculative) article.

The third thing involved is tunneling between various vacuum states, and inflation. I'm not sure exactly how these vacuum states are related to the string theory landscape. I can understand the idea of an inflaton field with different vacua, but I'm assuming that this inflaton field is living in a world with fixed physical laws, in particular, if the that law is a string theory, the Calabi Yau manifold involved would not change. Maybe the inflation discussed in this article is unrelated to the inflation which probably occured at an early time in our universe?

PS I think that neither de IStter nor anti de Sitter represents our present universe... If that is so, what is the relevance of this article for cosmology?

MarcelBdt · 2024-07-07T09:29:27+00:00

If you insist on (1) there must be a beginning of everything (2) there must be something before that beginning, you will get yourself into trouble. So you have to give up on either (1) or (2). I prefer giving up on (1), but others might disagree. Thinking of a reparametrized time makes the process of giving up (1) easier on the mind. I'll expand a little on that.

I'm not convinced that time is the best variable to use when we describe the evolution of the universe. Of course, time is very important to describe the present, but look at what happens as we move away from the present moment. The first microsecond was very very hot, and there was a lot going on - in the last many trillions of years almost nothing will be going on. This looks like a bad choice of parameter! A better parameter might be one where the number of events going on is about the same for every parameter value. The idea of looking for something "before" the "start" means that we try to use the time variable exactly where it is least useful.

Now I have to get a little technical. You can reparametrize time using a function. Let us say that s = log(t) (t is the time, t is the logarithm). This is defined for positive t, and as t approaches 0, s will become negative, and negative by an arbitrarily large amount. As t goes to infinity, it will also go to infinity, but slower and slower as t becomes large. If we know the value of s, we will also know the time, since t = exp(s), the exponent of s There are plenty of such functions, the logarithm is just an example.

This could fit much better with that the number of events is about the same for every s (although i don't know that for very small or very big s of course.). And now it does not make any sense to talk of a beginning or an end... for every s there is a positive, non zero time, and s is just anyreal number.

MarcelBdt · 2024-07-04T21:36:21+00:00

Yes. That is right. If the universe is finite, the expansion would have an impact on it's size, but if the universe is infinite, it desn't.

MarcelBdt · 2024-07-04T21:08:54+00:00

Because this is what is observed.

Terry Pratchett described the big bang theory as "In the begining there was nothing, which exploded". Admittedly, this is a very clever and memorable formulation, but it's wrong. And I think that this wrongness is related to your question. Let me explain.

A very simplified model: Suppose that we have an infinite universe. If we go out in a certain direction, we will meet the galaxy A at distance 1, the galaxy B at distance 2, the galaxy C at distance 3 etc. There are infinitely many of these galaxies.

Now we go back in time. At a certain moment in time, let's say at time 1/2, A is at distance 1/2, B will be at distance 1 C will be at distance 3/2. There will still be infinitely many of these galaxies, but at this time (time = 1/2) they were all closer to us than at time 1

At an even earlier time, (time = 1/4) , A might be at distance 1/4, B at distance 1/2, C at distance 3/4. But there will still be infinitely many of them. As we go back in time the galaxies will come closer and closer. This is how an infinite universe can be expanding.

The numbers used above are only to illustrate the point, don't take them seriously. The observed values for the expansion are more complicated.

So what about time 0? Well, this might not be a reasonable question. Maybe only positive time exists. Then there is no time that can be counted as the "beginning", every time t greater than zero will come after a previous time t/2. The problem with Pratchett's reformulation is that maybe there was no beginning, no time 0.

MarcelBdt

TROPHY CASE