What is "time"

[PhysBang]

No it isn't some alternative theory. See the tilted lightcones here.

The lying-through-citation is getting really bad here. Please read your citations, Farsight. How does that page describe the "tilt" that Farsight loves? As spacetime curvature. "We have a black hole when the curvature of spactime becomes so severe that, for some region, there is no path out of that region that remains inside its own lightcones." Like in the first citation that Farsight used to introduce "tilt", the author(s) describe gravity as spacetime curvature.

Go and read Einsten's Leyden Address where he referred to inhomogeneous space.

Please, do any physics problem or application with inhomogeneous space.

 

[Billy T]

... Like in the first citation that Farsight used to introduce "tilt", the author(s) describe gravity as spacetime curvature. ...

Yes that POV is necessary for complete accuracy as Newton's inverse square is very slightly wrong, but still good enough that the New Horizons space craft that my 30 year employer, APL/JHU launched 10 years ago towards Pluto only used Newton's version of gravity and will pass thru, after more than 3 billion miles of travel to its target, a 120 mile diameter circle before its close fly by on 15 July 2015. That aim accuracy is equivalent to an arrow fired from 100 miles away hitting a dime!

They will try to "wake up" the satellite again in a few days and then reflected Pluto light will guide it to a very close fly-by. I think, soon after wake up it will begin taking photographs. When closer*, many non-photographic data will be collected too. After the fly-by, when power is available for telemetry, it will take nine months just to send the huge volume of data back to earth - low power from its radio-isotope "battery" and the great distance limits the data rate.
Newton may be wrong about the math of gravity, but is "good enough for government work" as we say, and it is still mass that is the source of gravity.

The only AFAIK astronomical observations not well described (to experimental accuracy limits) are (1) the very slight bending of star light (appearant positon of the star) during a total eclipse of the sun** and (2) very fine details about Mercury's rate of precession.

* APl's 10 year old MESENGER satellite has orbited mercury only 16 miles above the surface! but on 24 October 2014 needed and got a boost to higher altitudes as atmospheric drag would soon send it crashing into the surface. It took radar photographs of, thru the constant thick clouds, with each pixel only 100 miles wide. It surprisingly is energetically more difficult to go to Mercury than Pluto. APL I think is the only organization that has done both. APL has designed about 250 or more satellites that have been launch with a specular success record that caused NASA to take this Pluto missions away for JPL. Often APL has delivered on time an under budget! Compared to JPL, APL is tiny.***

** Observation of that tiny shift were first made in Brazil and Africa. In one the shift was too small to be measured with the film's resolution and the dynamic atmospheric refraction or "twinkle" of the star. (Conditions for observing were poor.)

*** More details of some of APL's amazing history in space here: http://www.sciforums.com/threads/interesting-facts-of-the-space-age.135996/#post-3251191

 

[Beer w/Straw]

So your GR denier?

I've already mentioned GPS

Although I was thinking about being a princess at the time.

 

[Beer w/Straw]

The thing is. I haven't corrected you already. Because I'm sure people know that your wrong.


Do you want me to quote three text books?

You brag you have a Ph D in physics, that doesn't matter at this point.

You should be banned.

 

[Beer w/Straw]

I'm right here.

You can respond to me. Unless you consider yourself too privileged.

Your only the type of person who would want to ruin my education.

 

[OnlyMe]

It's wrong. A concentration of energy, usually in the guise of a star or planet, is the cause of gravity. It alters the surrounding space, whereupon motion through it is modelled as curved spacetime.

All you have done above is exchanged energy for mass as the source of space-time cuvature.., you have not presented any fundamental mechanism that describes how.

My statement was that, space-time curvature as the cause of gravity, is a modern interpretation of GR, which I have come to believe is not accurate. My belief.., and note I did say belief because at this point no one knows with any certainty.., is that there is an underlying fundamental mechanism, likely within the context of QM that will better describe the origin of gravitation.., and GR along with space-time are and will remain accurate descriptions of the resulting gravitational field and how objects within a gravitational field interact.

Notice the difference in what I just said and your usual proclamations.., I make those statements as a matter of what I believe to be the case not as a statement of absolute knowledge. Until we arrive at a place that we are able to bridge the divide between GR and QM, we will not have any diffinitive answers....

 

[paddoboy]

it is still mass that is the source of gravity.

That's not strictly true. Spacetime curvature/warping in the presence of mass/energy is the cause of gravity.
Or as John Wheeler said....
Matter/mass tells Spacetime how to curve: Spacetime tells matter/mass how to move.

As far as the subject of this thread is concerned, and as I have shown throughout with links, without time, we would not be here. It's that which according to the current cosmology of the Universe, arose or evolved along with space, from the BB itself, and any amount of twisting, turning and squirming will not get away from that.
That is the premise of the BB.

 

[PhysBang]

So your GR denier?

I've already mentioned GPS

Although I was thinking about being a princess at the time.

Yeah, that post is a bizarre non sequitor, and not the first from that poster.

I agree, however, that Newton, Laplace, Euler, and many others did a fantastic job of developing Newtonian mechanics and showing just have amazingly accurate it is within the solar system. The change in the orbit of Mercury that provides evidence for GR is only 43/360 of a degree in the orbit of Mercury over the course of a century; Newtonian mechanics accounts for about 500/360 of a degree, from the interactions of the planets.

While deep space examples are dramatics, there are actually many tests inside of the solar system and there are many phenomena to measure the parameters of GR or other theores of gravity. (See, Clifford Will's Was Einstein Right? or his textbook on GR Theory and Experiment in Gravitational Physics. Or look up the Parameterized post-Newtonian formalism, which is a pretty neat example of theoretical-science-turns-observational-science.)

 

[Beer w/Straw]

As far as I know, Newtonion Mechanics was all that required for the moon landing.

 

[paddoboy]

As far as I know, Newtonion Mechanics was all that required for the moon landing.

As well as the Mar's robotic craft, Viking's, Spirit, Opportunity, Phoenix and Curiosity...not sure about New Horizons, but I believe that also along with the Jupiter and Saturnian probes.

 

[PhysBang]

As far as I know, Newtonion Mechanics was all that required for the moon landing.

Indeed. In 1903, Ernest Brown was able to use observations of the moon and Newtonian mechanics to fix the power law of gravity to 8 decimal places, ruling out the idea that the perihelion advance of Mercury was caused by a different value of the power law.

 

[Farsight]

All you have done above is exchanged energy for mass as the source of space-time cuvature.., you have not presented any fundamental mechanism that describes how.

I did it in the gravity thread. At the fundamental level, space and energy are the same gin-clear ghostly elastic thing. Space isn't nothing. When you inject energy you're effectively inserting space, so the result is a spatial pressure gradient.

My statement was that, space-time curvature as the cause of gravity, is a modern interpretation of GR, which I have come to believe is not accurate.

That's right. Spacetime curvature is a curvature in your plot of for example equatorial light clocks. The lower clocks don't go slower because of spacetime curvature, they go slower because a concentration of energy alters the surrounding space.

My belief.., and note I did say belief because at this point no one knows with any certainty.., is that there is an underlying fundamental mechanism, likely within the context of QM that will better describe the origin of gravitation

QM doesn't really describe anything very well.

and GR along with space-time are and will remain accurate descriptions of the resulting gravitational field and how objects within a gravitational field interact.

Fair enough.

Notice the difference in what I just said and your usual proclamations.., I make those statements as a matter of what I believe to be the case not as a statement of absolute knowledge. Until we arrive at a place that we are able to bridge the divide between GR and QM, we will not have any difinitive answers....

You speak from a position of ignorance, I don't. Get used to it. And start paying attention.

 

[Trippy]

QM doesn't really describe anything very well.

I laughed hard when I read this. The irony in this statement is as amazing as it is astounding.

 

[Farsight]

I laughed hard when I read this. The irony in this statement is as amazing as it is astounding.

Oh yeah? Then describe an electron.

 

[Trippy]

Oh yeah? Then describe an electron.

Your computer works fine right? Explain that without it, or the symmetry of a benzene ring...

 

[Farsight]

Come on, describe the photon. Or the quantum nature of light. Or the electron. Or its electromagnetic field. Or the positron. Or why the electron and positron move towards and around one another. Or why the electron and proton move as they do. Oh, and note that virtual particles are virtual, and hydrogen atoms don't twinkle.

Oh, and you know that speed of light thread of mine that you moved into the fringe section? Well, the Einstein Online guys have come good, so now I can give you screenshots to back up what I was saying. See below. So perhaps you'd like to move my thread back to the physics and maths section?

 

[Trippy]

So perhaps you'd like to move my thread back to the physics and maths section?

Nope.

 

[paddoboy]

You speak from a position of ignorance, I don't. Get used to it. And start paying attention.

Pot, kettle black!!!!!!

 

[paddoboy]

Come on, describe the photon.

The photon simply is the quanta of light and EMR.
They are never seen to be at rest and there speed is a constant 186,000M/sec in a vacuum, and which we denote as "c"

Electrons are elementary sub atomic particles, and is the carrier of what we call electricity.

 

[Trippy]

Come on, describe the photon.

A single quantum of light.

Or the quantum nature of light.

Light exists as discrete quanta, or packets (really, what's so hard about this?)

Or the electron.

A spin half fundamental particle with a negative electric charge, that behaves like a marble being shaken around an isotropic box when in the first orbit of an atom (subsequent orbits can also be described like marbles in boxes but require consideration of additional factors).

Or its electromagnetic field.

What's two describe? The electric field behaves as a point charge, the magnetic field behaves as a dipole.

Or the positron.

What's to describe? As near as we can tell it's identical to an electron, but with opposing charge. Everything that applies to an electron, as far as we can tell, also applies to it.

Or why the electron and positron move towards and around one another.

Faraday's law, conservation of angular momentum.

Or why the electron and proton move as they do.

Conservation of energy - the interchange of potential energy and kinetic energy combined with its behavior as a marble being shaken about its box - essentially using the approach of considering a marble being shaken around a potential well. This all means that if we divide the space around a hydrogen nucleus into a bunch of tiny cubes, then each cube has a probability of finding the electron in it as it moves. The electron has a higher probability of being found close to the nucleus than it does away from it, however, if we examine the radial probability - the total probability at each radius, we find that the electron has a preferred radius that it likes to sit at. This is because as you move further from the nucleus, although there are more cubes, the probability of finding the electron in them decreases which creates a peak. I can (and have) illustrated this behavior using a spreadsheet.

Oh, and note that virtual particles are virtual, and hydrogen atoms don't twinkle.

I don't know why you felt compelled to include this, this is only relevant to a part of quantum mechanics.