That is not part of relativity.student34 said:In relativity, is there known to be an intrinsic relationship. For example, we know that a proton and an electron have an intrinsic relationship of mass.
What are you referring to here?student34 said:we know that a proton and an electron have an intrinsic relationship of mass.
I do not know, what you mean by "intrinsic relationship". Elementary particles by definition are described by realizations of irreducible representations of the proper orthochronous Poincare group in terms of local fields. This implies that each particle is classified with the corresponding qualifiers of these representations, i.e., mass (squared), ##m^2 \geq 0##, and Spin ##s## (leading to ##2s+1## polarization-degrees of freedom for massive and ##2## for ##s \geq 1/2## and ##1## for ##s=0## pliarization-degrees of freedom for massless particles).student34 said:In relativity, is there known to be an intrinsic relationship. For example, we know that a proton and an electron have an intrinsic relationship of mass.
Interesting way to think about this. But that just seems to be the geometry of the object's world line rather that an intrinsic difference of the "distance".jbriggs444 said:If you have two events with a space-like separation, you cannot get a physical object to go from one to the other. If you have two events with a time-like separation, you can.
Can't we measure the same thing two different ways?Nugatory said:It is pretty obvious that the two are not interchangeable because one is measured with a clock and the other with a meter stick. Therefore any correct theory will imply that; if you want to call this a statement about what the theory “must” do, you may.
If all world lines have this characteristic, it becomes useful to treat it as a global property rather than a one-off observation.student34 said:Interesting way to think about this. But that just seems to be the geometry of the object's world line rather that an intrinsic difference of the "distance".
Thanks, I started reading the Bondi K-calculus linkrobphy said:There are more precise ways of describing what many of us are trying to tell you,
by using dot-products (which could be regarded as a way to geometrically formalize
measurements of physical quantities [modeled as geometrical objects]
with various measuring devices [modeled as certain unit vectors],
then making definitions).
The use of geometric units is done for consistency and convenience,
but one needs sufficient background understanding to see this.
In my opinion, to appreciate this viewpoint,
you need to understand the basics of spacetime geometry,
as presented in
Taylor and Wheeler's "Spacetime Physics (1st ed)" linked above.
However, I think you may benefit from
Bondi's "Relativity and Common Sense" first
because it emphasize the operational definitions of "time" and "space" coordinates
using light-rays and clocks,
and postpones the formulas and formalism (and use of geometric units) until later.
Until then, I think you are just getting caught up in the formalism
because you don't understand what the basics are (why relativity is formulated the way that it is).
Shameless plug? https://www.physicsforums.com/insights/relativity-using-bondi-k-calculus/
my $0.03
Just a meter with no other combination seems much more specific, but I am not saying that they necessarily have to be the same thing just because they are both using the same unit.PeroK said:Well, torque and energy have the same units (Newton-metres). They are not the same thing. One ##Nm## of torque is not interchangeable with one ##Nm## of energy.
This is interesting. I did not know this.PeroK said:Also, if we continue with geometric units in relativity, we have mass measured in metres as well. The mass of the Sun, for example, is about ##1.5 \ km##. That's something different again from a spacelike interval of ##1.5 \ km##.
I was just giving an example of what kind of relationship I am looking for when it comes to a meter of time and a meter of distance.PeterDonis said:What are you referring to here?
In what ways are time and space related? More specifically, in what ways is a separation between two points on a timelike interval the same as the separation between two points in space?vanhees71 said:I do not know, what you mean by "intrinsic relationship".
I meant that that would not seem to necessarily mean that the two "distances" were different .jbriggs444 said:If all world lines have this characteristic, it becomes useful to treat it as a global property rather than a one-off observation.
If GR were the theory of everything and had no paradoxes (like the grandfather paradox) I would agree.jbriggs444 said:On the other hand, it seems pointless to discuss further. The theory works. Shut up and calculate already.
That doesn't help, because I don't know what kind of relationship you are even talking about when you say:student34 said:I was just giving an example of what kind of relationship I am looking for when it comes to a meter of time and a meter of distance.
What kind of relationship are you talking about here? There is no such relationship in physics that I am aware of.student34 said:a proton and an electron have an intrinsic relationship of mass.
What are you talking about here? There is no "grandfather paradox" in GR. All solutions in GR are self-consistent.student34 said:If GR were the theory of everything and had no paradoxes (like the grandfather paradox)
There aren't any. Timelike intervals and spacelike intervals are fundamentally different. No matter how many times you try to ask about this in different words, the answer is not going to change. Why is this such a problem?student34 said:in what ways is a separation between two points on a timelike interval the same as the separation between two points in space?
They both have mass. That is their intrinsic relationship. Or more specifically, they both have that as an intrinsic property.PeterDonis said:That doesn't help, because I don't know what kind of relationship you are even talking about when you say:What kind of relationship are you talking about here? There is no such relationship in physics that I am aware of.
Ok.student34 said:They both have mass.
This doesn't seem like a very useful use of language. You could just as well say that you and I have an "intrinsic relationship" because we both have mass. What does that tell us? Nothing of any use. Certainly there is no "intrinsic relationship" of this kind in any actual physics. Knowing that the proton and electron both have mass doesn't tell you anything else about them or about their relationships.student34 said:That is their intrinsic relationship
Actually, they don't. The mass of the proton comes from the masses of its quarks plus the energy contained in the strong interaction field that binds the quarks together.student34 said:they both have that as an intrinsic property.
Apparently GR allows time travel. Michio Kaku talks about the grandfather paradox in this video . Start watching at 1:30.PeterDonis said:What are you talking about here? There is no "grandfather paradox" in GR. All solutions in GR are self-consistent.
I think you have read way too much pop science and not enough actual science.
GR has solutions with closed timelike curves, yes. Most physicists consider those solutions to be physically unreasonable. However, even these solutions are mathematically self-consistent and no grandfather paradoxes are possible.student34 said:Apparently GR allows time travel.
This video is most certainly not a valid reference for PF discussion. Kaku is giving his personal opinions, not stating what GR says. He might well be giving the impression that he is stating what GR says, but that just underscores why videos like this are not valid references. Kaku and others (Brian Greene is another frequent offender) will say things in these videos that they know they could never get away with in an actual peer-reviewed paper, because the people who would review his work in a peer-reviewed paper know what the actual physics, like GR, says, and will call him on it if he misstates or misrepresents things.student34 said:Michio Kaku talks about the grandfather paradox in this video
Interesting, I did not know that.PeterDonis said:Actually, they don't. The mass of the proton comes from the masses of its quarks plus the energy contained in the strong interaction field that binds the quarks together.
The mass of quarks and electrons comes from their interaction with the Higgs field as a result of electroweak symmetry breaking; in the very early universe, before electroweak symmetry breaking happened, quarks and electrons were massless.
None of this changes what I said above.
Ok, then that is where it stands.PeterDonis said:There aren't any. Timelike intervals and spacelike intervals are fundamentally different. No matter how many times you try to ask about this in different words, the answer is not going to change. Why is this such a problem?
Ok, fair enoughPeterDonis said:GR has solutions with closed timelike curves, yes. Most physicists consider those solutions to be physically unreasonable. However, even these solutions are mathematically self-consistent and no grandfather paradoxes are possible.This video is most certainly not a valid reference for PF discussion. Kaku is giving his personal opinions, not stating what GR says. He might well be giving the impression that he is stating what GR says, but that just underscores why videos like this are not valid references. Kaku and others (Brian Greene is another frequent offender) will say things in these videos that they know they could never get away with in an actual peer-reviewed paper, because the people who would review his work in a peer-reviewed paper know what the actual physics, like GR, says, and will call him on it if he misstates or misrepresents things.
basically, for two timelike separated events there is in principle a massive object that can move from the first event to the last. For two spacelike separated events, instead, a such body there is not.PeterDonis said:Timelike intervals and spacelike intervals are fundamentally different.