CompassRed @ CompassRed @discuss.tchncs.de

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Imaginary numbers are no more imaginary than real numbers. The name trips a lot of people up. If you want to call imaginary numbers "dark unicorns" then you really should say the same thing of the numbers 1, 2, and all other numbers as well.

You're thinking of topological closure. We're talking about algebraic closure; however, complex numbers are often described as the algebraic closure of the reals, not the irrationals. Also, the imaginary numbers (complex numbers with a real part of zero) are in no meaningful way isomorphic to the real numbers. Perhaps you could say their addition groups are isomorphic or that they are isomorphic as topological spaces, but that's about it. There isn't an isomorphism that preserves the whole structure of the reals - the imaginary numbers aren't even closed under multiplication, for example.

You're mistaken unfortunately. The books don't start that way. They start by describing Arthur Dent's house.

It's supposed to be E^{2 = (mc}2 )^{2 + AI}2 , which implies that AI = pc, because AI is the momentum that will carry us into the future. These rookies clearly just took the square root using freshman's dream.

Yeah, you're close. You seem to be suggesting that any measurement causes the interference pattern to disappear implying that we can't actually observe the interference pattern. I'm not sure if that's what you truly meant, but that isn't the case. Disclaimer: I'm not an expert - I could be mistaken.

The particle is actually being measured in both experiments, but it's measured twice in the second experiment. That's because both experiments measure the particle's position at the screen while the second one also measures if the particle passes through one of the slits. It's the measurement at the slit that disrupts the interference pattern; however, both patterns are physically observable. Placing a detector at the slit destroys the interference pattern, and removing the detector from the slit reintroduces the interference pattern.

Binary supremacy!!!!!!!

Of course! I'm always excited for an opportunity to discuss these sorts of things, so I should be thanking you instead.

I'll preface this with the fact that I am also not a physicist. I'm also simplifying a few concepts in modern physics, but the general themes should be mostly accurate.

String theory isn't best described as a genre of physics - it really is a standalone concept. Dark matter and black holes are subjects of cosmology, while string theory is an attempt to unify quantum physics with general relativity. Could string theory be used to study black holes and dark matter? Sure, but it isn't like physicists are studying black holes and dark matter using methods completely independent from one another and lumping both practices under the label string theory as a simple matter of categorization.

You are correct to say that string theory is an attempt at a theory of everything, but what is a theory of everything? It's more than a collection of ideas that explain a large swath of physical phenomena wrapped into a single package tied with a nice bow. Indeed, when people propose a theory of everything, they are constructing a single mathematical model for our physical reality. It can be difficult to understand exactly what that means, so allow me to clarify.

Modern theoretical physics is not described in the same manner as classical Newtonian physics. Back then, physical phenomena were essentially described by a collection of distinct models whose effects would be combined to come to a complete prediction. For example, you'd have an equation for gravity, an equation for air resistance, an equation for electrostatic forces, and so on, each of which makes contributions at each point in time to the motion of an object. This is how it still occurs today in applied physics and engineering, but modern theoretical physics - e.g., quantum mechanics, general relativity, and string theory - is handled differently. These theories tend to have a single single equation that is meant to describe the motion of all things, which often gets labeled the principle of stationary action.

The problem that string theory attempts to solve is that the principle of stationary action that arises in the quantum mechanics and the principle of stationary action that arises in general relativity are incompatible. Both theories are meant to describe the motion of everything, but they contradict each other - quantum mechanics works to describe the motion of subatomic particles under the influence of strong, weak, and electromagnetic forces while general relativity works to describe the motion of celestial objects under the influence of gravity. String theory is a way of modeling physics that attempts to do away with this contradiction - that is, string theory is a proposal for a principle of stationary action (which is a single equation) that is meant to unify quantum mechanics and general relativity thus accurately describing the motion of objects of all sizes under the influence of all known forces. It's in this sense that string theory is a standalone concept.

There is one caveat however. There are actually multiple versions of string theory that rely on different numbers of dimensions and slightly different formulations of the physics. You could say that this implies that string theory is a genre of physics after all, but it's a much more narrow genre than you seemed to be suggesting in your comment. In fact, Edward Witten showed that all of these different string theories are actually separate ways of looking at a single underlying theory known as M-theory. It could possibly be said that M-theory unifies all string theories into one thus restoring my claim that string theory really is a standalone concept.

This problem doesn't involve cardinal numbers.

You have the spirit of things right, but the details are far more interesting than you might expect.

For example, there are numbers past infinity. The best way (imo) to interpret the symbol ∞ is as the gap in the surreal numbers that separates all infinite surreal numbers from all finite surreal numbers. If we use this definition of ∞, then there are numbers greater than ∞. For example, every infinite surreal number is greater than ∞ by the definition of ∞. Furthermore, ω > ∞, where ω is the first infinite ordinal number. This ordering is derived from the embedding of the ordinal numbers within the surreal numbers.

Additionally, as a classical ordinal number, ω doesn't behave the way you'd expect it to. For example, we have that 1+ω=ω, but ω+1>ω. This of course implies that 1+ω≠ω+1, which isn't how finite numbers behave, but it isn't a contradiction - it's an observation that addition of classical ordinals isn't always commutative. It can be made commutative by redefining the sum of two ordinals, a and b, to be the max of a+b and b+a. This definition is required to produce the embedding of the ordinals in the surreal numbers mentioned above (there is a similar adjustment to the definition of ordinal multiplication that is also required).

Note that infinite cardinal numbers do behave the way you expect. The smallest infinite cardinal number, ℵ₀, has the property that ℵ₀+1=ℵ₀=1+ℵ₀. For completeness sake, returning to the realm of surreal numbers, addition behaves differently than both the cardinal numbers and the ordinal numbers. As a surreal number, we have ω+1=1+ω>ω, which is the familiar way that finite numbers behave.

What's interesting about the convention of using ∞ to represent the gap between finite and infinite surreal numbers is that it renders expressions like ∞+1, 2∞, and ∞² completely meaningless as ∞ isn't itself a surreal number - it's a gap. I think this is a good convention since we have seen that the meaning of an addition involving infinite numbers depends on what type of infinity is under consideration. It also lends truth to the statement, "∞ is not a number - it is a concept," while simultaneously allowing us to make true expressions involving ∞ such as ω>∞. Lastly, it also meshes well with the standard notation of taking limits at infinity.

My superiority complex is stronger than your inferiority complex.

I like this one

I don't know the reason. I think not having the extra blank lines would be better, but it works just fine as is - even the post admits this much. That's why it's an enhancement. It's possible for software to be functional and consistent and still have room for improvement - that doesn't mean there is a bug.

My point is that someone made the decision for it to do that and that the software works just fine as is. It's not a bug, it's just a weird quirk. The fact that they made the enhancement you requested doesn't make the old behavior buggy. Your post title said "it's not a bug, it's a feature!", but the behavior you reported is not accurately classified as a bug.

It's not a bug just because the software doesn't conform to your personal preferences. You're asking for what would be considered an enhancement - not a bug fix.

It depends. If the variable names are arbitrary, then a map is best. If the variable names are just x_1, x_2, x_3, ..., x_n, then a list or dynamic array would be more natural. If n is constant, then a vector or static array is even better.

I don't recall any socialized courier or food delivery services.

I see what you're saying about moving away from smarmy pop culture videos, but the claim that all the "random smart things" ultimately don't matter is weak when you're comparing them to topics that literally do not matter at all. I'm not invalidating your example, just pointing something out.

This is just a continuous extension of the discrete case, which is usually proven in an advanced calculus course. It says that given any finite sequence of non-negative real numbers x,

lim_n(Sum_i(x_i^{n ))}(1/n)=max_i(x_i).

The proof in this case is simple. Indeed, we know that the limit is always greater than or equal to the max since each term in the sequence is greater or equal to the max. Thus, we only need an upper bound for each term in the sequence that converges to the max as well, and the proof will be completed via the squeeze theorem (sandwich theorem).

Set M=max_i(x_i) and k=dim(x). Since we know that each x_i is less than M, we have that the term in the limit is always less than (kM^{n )}(1/n). The limit of this upper bound is easy to compute since if it exists (which it does by bounded monotonicity), then the limit must be equal to the limit of k^{(1/n)M. This new limit is clearly M, since the limit of k}(1/n) is equal to 1. Since we have found an upper bound that converges to max_i(x_i), we have completed the proof.

Can you extend this proof to the continuous case?

For fun, prove the related theorem:

lim_n(Sum_i(x_i^{(-n) ))}(-1/n)=min_i(x_i).

2 may be the only even prime - that is it's the only prime divisible by 2 - but 3 is the only prime divisible by 3 and 5 is the only prime divisible by 5, so I fail to see how this is unique.