# pmb

Senior Members

379

1. ## What is Time?

I can't tell what you know or don't know. However it seems to me that you don't know what a space is in the mathematical sense of the term. You seem to keep confusing it with the familiar meaning of the word as in the set of all spatial locations. For example: (1) Let p = pressure and v = volume. The pv diagram used in thermodynamics is a type of space whose points are (p, v) which have nothing to do with the normal meaning of space. But the (p, v) are elements of that space. (2) We call a set of values x1, x2, ..., xN a point. The variables x1, x2, ..., xN are called coordinates.
2. ## What is Time?

Yes. Time is very much the fourth dimension of spacetime. I explained all of this above. Spacetime is also known as Minkowski space. But this is a different use of the term "space" than the typical physical meaning. Its a mathematical space. Mathematical spaces don't neccesarily represent space as in the "spatial" kind of space. Minkowski space is a good example of that. Its not the "spatial" kind of space but a mathematical space. And its quite true that time is a dimension in that mathematical space. But you shouldn't be confusing the two kinds of meanings of the term space and it seems
3. ## Another short question.

The following definition of observer is from A first course in general relativity by Bernard F. Schutz, page 4 I don't see that there needs to be an observer in quantum mechanics, just something that can make measurements. But if it is required then the above should work fine.
4. ## What is Time?

I know what you believe. Now I want to know why you believe it. What do you think it means to say that time is a dimension in space, i.e. a spatial dimension? What I don't get is why don't you think that space is a temporal dimension? Taylor and Wheeler write on page 18 of Spacetime Physics You know what space is, right? Loosely stated, it's the totality of "points." Each point in space is identified by exactly three numbers, i.e. it takes three numbers to specify the position vetor R = (x, y, z). Time is what we read on a clock. A time reading is not used to identify a point in
5. ## What is Time?

I disagree. A point in Minkowski space is denoted as follows X = (time, space). This is an element in spacetime. It is not an element in space. Its only mathematically that the temporal variable is in some ways treated like the spatial variables. But in no way can it be called a spatial dimension. Please eleborate on why you believe that time is a spatial variable. Thanks.
6. ## Ad Hominem

It appears that you might have missed what swansont and I were discussing. The term personal attack is not taken as the word "person" acting on "attack". I.e. personal attack is a term which does not mean attack on a person. I have a text which defines these terms. On this point it says Do you see how this is not the same as attack on a person?
7. ## Why is there a reputation system?

I intentionally left it out so that this wouldn't get persaonal. Had she not said anything, which is what I was hoping, then this wouldn't be dragging anybody into it. It was intended to be abstract and as such I'l say whatever I please, so long as I don't mention particular people. And as I said, I will never read anything of her's again, including posts. And I mentioned that it was a moderator, not that someone told me something in their capacit of moderator. I mentioned it because it would have no meaning withoug it because the subject was about moderators having access to what we rep.
8. ## What is Time?

I believe that you believe exactly what you say. And I've researched this many many years ago. Eintein had something to say about this as does Tolman. From A Brief Outline of the Developement of the Theory of Relativity, by Albert Einstein, Nature, No. 2677, Feb 17, 1921. From Relativity, Thermodynamics and Cosmology by Richard C. Tolman, page 29 These points eloquently state my position on this subject.
9. ## Why is there a reputation system?

I would never have brought it up unless I didn't already get a PM from a moderator who questioned my use of the reputation system and then negatively judged me about who and why I +repped someone. They claimed I was abusing the system. I won't have that kind of crap in my life. I consider if to be very offensive. In fact the same moderator called me immature for reporting someones insults because I'm "too sensitive" and they don't even know me. I'll let you in on something personal. Life has pounded the crap out of me. Aftrer getting Leukemia I damaged my back so I'll have to live on const
10. ## Why is there a reputation system?

Yes. That hasn't been mentioned in this thread yet so I'm glad that you brought it up/ Moderators not only know who's repping who but the also appear to be sitting injudgement of us when we use the rep system. Let it be known that I will never rep anybody again for this reason. I don't like being spyed on and then judged from the results.
11. ## What is Time?

Space refers to where things are. A time parameter doesn't tell you anything about where something is. That's why its not a spatial dimension. Be careful not to confuse "space" in the mathematical space from "space" in the physical sense. People have a tendancy to confuse these two usages
12. ## What is Time?

No. Time is not simply that which pertains to a particular system. Time pertains to the universe in its entirety. As Aethelwulf pointed out a system can be static but that doesn't mean that time has stopped in that frame. Frames are infinite in size. Just because a box in intergalactic space is static and thus unchaning in time it doesn't mean that time has stopped. There's an entire universe of change going on around it. I disagree. Time is not a spatial dimension. Its a dimension in spacetime. Spacetime is a space in the mathematical sense of the term but time is not a spatial dimensio
13. ## What is Time?

True, but that doesn't mean that time doesn't pertain to changes, You can only speak of a stationary state when you have a clock to compare it to. A.P. French speaks about time in his text Newtonian Mechanics[/i]. On page 61-62 he writes Of course that depends on how the term physical is defined. Different people have different ideas of what it means to be physical. When I use the term it means that its something that is directly related to something in nature that has an existance. In this case the chaning of the universe as a whole. If i was talking about velocity then that's a m
14. ## What is Time?

Time does not refer to a particular system but to the universe as a whole. That means that somewhere in the universe something is changing. The sun is giving off energy, galaxies a moving away frmo each other, water pours over waterfalls, hearts are beating, cars race down the highway, the lab clock ticks away, radioactive material is decaying, paint is oxidizing, people fall in love, they work, pay bills, go food shopping, watch tv etc. The list goes on ad infinitum. When a quantum system is stationary it means that when you compare it to the ticking of a clock the quantum state is indepe
15. ## What is Time?

Time is a number, not a vector. The term scalar refers to a number which remains unchanged by a change in cordinates. A 4-scalar in relativity refers to a number which is independant on the choice of spacetime coordinates. A 3-scalar is a number which remains unchanged by a change in spatial coordinates. Time is a 3-scalar.
16. ## What is Time?

I agree. In fact that is the essence of what appears in that link.
17. ## Ad Hominem

The moderator is trying to tell you that your opinion on my writing style is your own and he doesn't share it. Have you ever heard of the term Doublespeak? Its defined as follows When you write This is very close to being doublespeak. It can only be read as meaning that without taking a step back, i.e. continuing as is, that I'm being an immature human being. I.e. its a veiled attempt at calling me immature. Besides, nobody asked for your opinion and it'd be unwise to think that kind of "advice" would be desired by any reasonable person. That's most likely why it got a neg rep.
18. ## What is Time?

I disagree. The very essense of time is directly related to change or "happenings". A friend of mine wrote an article on this topic. See http://www.wfu.edu/~brehme/time.htm. I agree with everything in that page. If there were a universe in which nothing happened and nothing changed then time would have no meaning.
19. ## In the absence of a heat source how long would it take for the earth to freeze solid?

Note: The term you're looking for is thermal energy, not heat. The thermal energy due to pressure would eventualy dissipate. The thermal energy due to pressure is from the process of compression. That's a finite process.
20. ## Why is there a reputation system?

And what about everyone here who gets a sick feeling in our stomach when you won't cease talking about someones dead mother, even after comments by the moderators? Just because you don't like someone it doesn't mean you have to make your beef with him public. That's not what forums like this are for. Please show a little decorum.
21. ## Particle wave duality

studiot - It's not just EM waves that are quantized. The electromagnetic field itself is quantized, even when the field is static.That's what Quantum Field Theory (QFT) is all about. See http://en.wikipedia.org/wiki/Quantum_field_theory Also, while its quite true that electrons are called particles it doesn't mean that they behave like a particles.
22. ## Fields and dimensions

Well said. Let's start from scratch. We call a set of values x1, x2, ... , xN a point. The variables x1, x2, ... , xN are called coordinates. The totality of points corresponding to all values of the coordinate with certain ranges constitute a space of N dimensions.
23. ## Ad Hominem

I'm glad we could discuss all this in a polite fashion and come to the resolution. Thanks for the conversation!
24. ## Fields and dimensions

To evaluate the field one needs to specialize the location in space r = (x, y, z) which to evaluate the field and the time t which it is evaluated. That mean we need to know the position vector of the location and that requires three numbers to uniquely specify it. The field is then expressed as E = E(r, t) This is what it means to speak of three spatial dimensions. This can be expressed as E = E(x, y, z, t) The element [v]X[/b] = (ct, x, y, z) is called a point in spacetime. Its also a position 4-vector. It requires 4 numbers to specify a point in spacetime. In relativity on
25. ## Ad Hominem

Please reread post #54 http://www.scienceforums.net/topic/67396-ad-hominem/page__view__findpost__p__687947 I think I see the source of our disagreement. You use the term personal attack to mean attack on a person. This is not what how the text, and several online sources, defines it. My text reads Note that it doesn't call the fallacy the "personal attack fallacy" but merey calls it a personal attack. By the way, you keep saying that this is my definition. Its not. Its how its defined in this text and elsewhere on the internet. Its the text that I use as an authoritative source
×