geordief

1 hour ago, Mordred said:

Confucius says, "It is only when a mosquito lands on your balls, that there is a way to solve problems without violence"

If only the same could be said of ticks(on the bell end).

26 minutes ago, MigL said:

Those coefficients define ease or effort for radiation to pass through that medium ( or lack thereof ).
For example, when we say the index of refraction of free space is 1, as opposed to glass at 1.5, is n=1 a property of space ?
Or is it a lack of that property.

Is the "medium" of free space the radiation itself?

Those coefficients apply to em radiation: Are there forms of radiation that apply to other fields (as per the fields in QFT)?

Eg does the strong force radiate?

1 hour ago, MigL said:

Communists(which Russia still claims to be

Can I just pick you up on that point?

I didn't think that Russia (you mean the regime ruling Russia now?)  claimed to be Communists.

Not that I care very much what they claim to be ,as (a) actions speak louder and (b) lying is what they are best at.

Just surprised you might think that.

Regarding "fascism" it seems to me that what we have in Russia and possibly emerging in  USA may  actually be worse than the fascism as practiced in the 20th century.

(Not quite sure if it was just Italy that calledcutself fascist or whether Spain shared the same,or similar  ideology)

2 hours ago, exchemist said:

It has always struck me as rather surprising that empty space should have quantitatively measurable properties, such as  e₀ and µ_0.   

Is there such a thing as "empty space"?

If "it"

is permeable  or permittive  then it has a property/properties  .

Can anything with properties be considered "empty"?

And if it is permeable/permittive  then does that mean it it "permeated"? -(with radiation?)

10 hours ago, MigL said:

Now you might ask "how is the temporal dimension converted to a distance".
It is multiplied by a 'conversion' factor c , and because it must be orthogonal to the three spatial dimensions, we make it imaginary

Is that a bit of "back engineering"

Was it Minkowski who arranged the axes so that they all had the same units of spatial distance?

Was he just trying to convert time to spatial distance or did be have in mind (as I always thought was  implied) that ct was the distance traveled by light  in the units of time chosen by the timepiece?

If it was him,did he explain his reasoning at the time?(not that we would need to respect his intentions ,necessarily if the model speaks for itself-I have read that  Einstein didn't  approve at first)

Would the model work as well if c was replaced with  an arbitrary speed such as ,for no particular reason   the speed of the earth around the Sun ?

Might it be that the quantative difference between the  overall spacetime interval and the integral of the causative chain of events is the  aging  and  spatial displacements of the sword?

If the sword was a smaller system  (and followed a geodesic?) would the difference be less?

Also is entropy another description of aging? 

edit ,am I just repeating what @md65536 posted a little above

8 hours ago, md65536 said:

Yes, a timelike spacetime interval is the square of the proper time measured by an inertial clock moving between the 2 events in flat spacetime.

If the sword remained at rest the whole time, and gravity was neglected, the interval would be the square of how much the sword aged between the two events.

34 minutes ago, MigL said:

The interval is the space-time distance between two events.
The path-history of the sword is its worldline.

Not necessarily the same.

Are they related?Can they be the same under any  particular conditions?

If the worldline  of an object is integrated is the result given in the same units as  the spacetime interval?(which just considers beginning and end points of the worldline,if I have that right)

Edit :just saw @KJW 's response.Probably too late to answer him today...

Imagine a pair of fictional events  the first being the murder of Caesar by one of his enemies using a sword  and the second fictional event the murder of JFK by someone using the same sword some 2000 years  later.

The spacetime interval between the two events is calculated  by choosing the earth as a reference frame ,measuring the distance between Rome and Dallas ,choosing the units of time and applying the s^2=(ct)^2-r^2 formula.

Suppose instead we were to follow the sword across the centuries  and make a note of the time and places in which it was recorded as having been prior to it being used again in the fictional killing of JFK.

Could we calculate spacetime intervals at every stop on the way,add them all up and end up with a figure that was comparable to the first spacetime interval when we just used the two events?

What if the sword had disappeared down a hole in the earth and reappeared in N. Zealand for a time (or had been taken to the moon and back) ?

Would that have increased the"cumulative" spacetime interval  even though the beginning and the end of its journey were still the same?

Sorry if that sounds a bit weird or overly tortuous 

31 minutes ago, Externet said:

Enjoy.

Before I saw the young girl ,I assumed  he was sitting on the jacks. 

1 hour ago, MigL said:

This discussion has its roots in Airbrush's claim that spatial expansion could be an explosion.
I don't think Airbrush ( or Swansont/Mordred/me ) define explosion as you have.
And while the mathematics you guys are posting are very interesting, and remind me of stuff I was once somewhat familiar with, they only match your definition , not the accepted definition of an explosion.

After all, if you define a man as a woman, then Bob's your ... aunt ??

If there are different possible definitions of explosions ,might there likewise be different definitions of expansion?

Is  @KJW basing his definition of an explosion on how things look to a test particle?

(as usual I have vanishingly little understanding  of this  subject  and so the question may not be pertinent)

28 minutes ago, Moontanman said:

IC, a bit of a sensational title for an actual discussion, poisoning the well I think. While I think Trump, IMHO, is accurately described as a rapist it is my opinion his "Bible sales" is nothing but a another grift and I find it odd that Christians in general don't find it tantamount to a slap in the face but rapist Bible?   

As an avid non reader of the Bible ,but having read that parts of the OT advocates some odious actions  can I ask if perhaps there are indeed some passages where rape is advocated, or described in an approving way?

Like the good lord I too am fishing ,but for evidence 

32 minutes ago, TheVat said:

I found the Dali's electrical problems kind of surreal.

 

(too soon?)

think so.

1 hour ago, swansont said:

This is only one frame. They must be moving with respect to each other to be different frames.

Well OK ,but can I repeat the question with just that one frame and the fixed distance between the location of the taker of the  measurements in the same frame? (I would have said "observer"  but I suspect that might have different meanings ...)

If you just have the one frame is there any way to find the concept of spacetime useful  as opposed to the pre relativistic separation of it into space and time?

Suppose we have two frames of reference that only differ  in that they are separated  by a fixed distance 

And suppose each frame makes measurements of an object that is moving relatively to both at any speed between 0 and c.

Is the concept of spacetime necessary for each frame to make that measurement and so that they agree in every case?

I am asking this because it has been said (was it by Minkowski?) that our previous till then  understanding of space and time must be replaced with a new amalgam  of the two (spacetime)  and I am wondering if this is because all frames of reference  are relatively in motion  in practice or whether the reason is deeper than that.

42 minutes ago, Mordred said:

While analogies can be useful, I've always found they tend to mislead.

  In this instance I have always found the method of describing spacetime curvature using geodesics paths of two parallel light beams far more useful.  If the two beams remain parallel then you have flat spacetime. If the beams converge the positive curvature. If they diverge then you have negative curvature. It's a simple descriptive provided you include the details that mass is resistance to inertia change as well as ensuring that the reader further understands that the (ct) interval is what provides time with dimensionality of length.

Is the region between,say  two BHs a region of negative curvature?(the two beams could diverge if the one moved towards the first CoG and the other beam towards the other)

I think I heard(from Markus ,perhaps if I remember rightly) that there are no  physical regions of negative  curvature and ,so it would just be a mathematical concept.

26 minutes ago, kenny1999 said:

I always thought that it was good to soak dirty clothes in water for hours before washing but recently I happen to find a lot of advice saying that it is not good to do that. What's the possible problem of soaking clothes in water? Would it weaken the fabric?

My guess is that it might make them lose their shape...

Edit:I was wrong.

12 minutes ago, Luc Turpin said:

Is the tread closed?

No

40 minutes ago, TheVat said:

I am guessing you never played the telephone game in childhood.

 

My mother was a Morse coder in WW2.Why I could never trust what she said.

1 hour ago, MigL said:

Can, or is, space-time really curved ?

Ouch ,did you mean to say "really"?.

I think it is just a mathematical construct to model real effects.

4 minutes ago, Luc Turpin said:

Finding life elswhere in the universe, without it either being brought to or coming from earth, would begin to help us also resolve the enigma.

Sadly (well happily enough) ,I don't think that will ever happen (unless we ever chanced upon a defunct civilization that left records)

Perhaps we could find intelligent life here on earth among the other species if we learn to communicate with them and they understood symbols....or even if they just helped us to understand our own intelligence. (the intelligence we use when our basic needs have been met) 

2 minutes ago, Luc Turpin said:

To me, life around us does not always follow a logical path, hence the need to make sense of it.

As for the before and after void, I like your use of the word "apparent", as we really do not know. 

However, if mind is within brain, then there isnothing waiting for us afterward. If mind acts upon brain, then, maybe.

I doubt there is a useful dichotomy between the mind and the brain.

To my view the brain is a part of the body  and  what the mind is    is very hard to understand.

On 3/17/2024 at 4:07 PM, KJW said:

That's a standard argument, but my argument is that the familiar gravity we recognise as Newtonian gravity is caused by time dilation, whereas the trampoline analogy indicates spatial curvature as the cause of gravity. Thus, the trampoline analogy is misleading about what causes gravity. A correct analogy that I discovered recently is two wheels of unequal radius joined by an axle. As this rolls along a flat road, the trajectory will curve towards the smaller wheel, and the larger the difference between the radius of the two wheels, representing time dilation, the larger the curvature of the trajectory, representing the acceleration we feel as gravity.

 

Can you explain (in simple terms for me and perhaps in greater detail for others) how time dilation causes gravity?

I thought time dilation was caused by relative motion  and that relative motion does not necessarily entail ,or cause  gravity.

So you can have time dilation  where there is no curved spacetime. 

16 minutes ago, Luc Turpin said:

 

Yes, if life has no meaning, then we are left with making our own sense of, and emphasise rationality and logic in doing so!

.....our own sense of it, and emphasize........

No ,the life we see around us follows logical paths .(animals,trees,humans,societies and the physical universe)

The senselessness I had in mind was the apparent void we come from  at birth and the void we enter after we are finished.

In between we try to understand  what our place is in that context.

I doubt other species entertain these ideas but ,who knows maybe they might.

"To Be or not to Be"

https://youtu.be/1u8OlUS7BhU?si=rMV91ELFEeaZncRA

 Or is the meaning of life to make sense of what has no sense?(we can all make sense of what seems  logical, I would  say)

13 minutes ago, Genady said:

Exactly.

In the spacetime, they both have curvature of about 1 lightyear radius:

Thanks.I did track down that passage in the  book.

For those of us who find it hard to visualise a curved 4d (3d+time) object  is the way to do this to break the 4d down into  all its 2d surfaces?

Would every surface need to be curved for the 4d object to be classed as such?

Or could in theory only one of eg spatial surfaces be curved and all the other surfaces be "straight" and the 4d construct would also be curved?(not that I expect such a thing to exist in nature)