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Thanks for reaching out. As you know, I'm not an expert, but I believe the answer is that clocks on the satellites are not synchronized with the ground.

I have not yet ID'ed anyone to weigh-in on this, but am working on it. Maybe there is someone in the forum who could comment?
This article should be helpful.

Here's my summary attempt...
-- Each GPS satellite has an atomic clock.
-- Each satellite is ranged from ground systems to get accurate locations for each.
-- The relativistic time differences are taken into account.
---- The orbital speed of the satellites require SR to calculate how much slower ground clocks run relative to the satellites, which is about 7 seconds per day.
---- Also, the orbital distances of the satellites require GR to calculate how much faster ground clocks run relative to the satellites, which is about 45 seconds per day.
---- So the net is about 38 seconds per day that must be taken into account.
 

DrJoePesce

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Happy Wednesday All!

This interesting item just crossed my desk:


Dimethyl ether detected by aLMA for the first time in a planet-forming disc (and the largest molecule detected to date). Regularly seen in star forming clouds, this is the first time it has been detected in a planet forming disc. The significance of this is that dimethyl ether is a building block for for more larger organic, prebiotic, molecules, like amino acids and sugars.
 
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Catastrophe

"There never was a good war, or a bad peace."
Dr Joe, a question for you Sir.

How is the BLOCK view of the Universe considered today.

As I understand it (and please correct me if I am wrong) a worldline is permanently present in the spacetime BLOCK. All points on any (all) worldlines are equally real. Our inability to perceive a worldline as a whole, forces us to take sequential views, meaning that we invent a travelling now. I know of no details of this proposed mechanism.
It may or may not be possible to access a 'time' other than now (dreams?), but we cannot alter anything, since the worldline already exists in its entirety.

It does rather make my head hurt!

Cat :)
 
Nov 18, 2019
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This article should be helpful.

Here's my summary attempt...
-- Each GPS satellite has an atomic clock.
-- Each satellite is ranged from ground systems to get accurate locations for each.
-- The relativistic time differences are taken into account.
---- The orbital speed of the satellites require SR to calculate how much slower ground clocks run relative to the satellites, which is about 7 seconds per day.
---- Also, the orbital distances of the satellites require GR to calculate how much faster ground clocks run relative to the satellites, which is about 45 seconds per day.
---- So the net is about 38 seconds per day that must be taken into account.
The article you mentioned and the quotes you presented seem irrelevant to my question:

Are all the atomic clocks on the GPS satellites and the clocks on the ground synchronized relative to the reference frame of each satellite and the ground frame after correction?

According to SR, the speed caused time dilation is relative i.e. is different observed from different reference frames, which can't be corrected to make the clocks synchronized relative to the reference frame of each satellite and the ground frame.
 

Catastrophe

"There never was a good war, or a bad peace."
Another question, if I may please, Dr Joe:

I have great problems with finding relative values of entropy for the singularity at the BB, and later in the development of the Universe. If the singularity has 'infinite' density/temperature et cetera I would have thought that the entropy would be very high? Yet, as the Universe expands, entropy must increase. (Assuming the Universe is a closed system). Why not BB to cold death?

Yet, we find a low degree of entropy in the Universe, with galactic structures, and stars instead of molecular clouds. And life, even, some of it projecting heat death for the Universe.

If we accept that physics breaks down as we approach t = 0, then what is the direction of entropy from the earliest moment that physics becomes valid?

Cat :)
 
Jan 29, 2020
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Hi Joe,
If you could put Large Hydron Collider in space would it be possible to use it to send small object or a cubesat 1 molecule at time to our neighboring solar system 4 light years away...
Thanks
A few planck lengths no prob. Some physics alters the trajectory: 1) Everything exerts gravity and is in motion enroute. An extra sunspot on AC(two) buffets some dust out later and now gravity in the system is different and it plays a mini-version of Armageddon's Lunar torque effect on the doomsday asteriod.
2) Yarkovsky Effect on the molecule. 3) Light heating's non-Yarkosky Effects. 4) Nanodust impacts. Plasma spheres the molecules pass through en route (Heliopause) might even stop the molecules cold. Subatomic particle impacts. Dust/soot collisions. Any variability of nearby stars affects the search space and state space of each molecule's trajectory. Consider space time is made of energy occasionally creating new subatomic particles and these are likely to impact the molecules eventually.H2 deeper space density is one atom every 4m^3 or something. Stuff becoming polarized in space is alot like the forces that would buffet the molecules.

My thread question is are there any moons in the Jovian system far enough away for manned exploration, from the radiation Jupiter and Io send outwards? Thx.
 
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Catastrophe

"There never was a good war, or a bad peace."
Hi Cat! I think this is correct. It does make the head hurt, no?
Hi. I assume this relates to #54 and not #57. I apologise for the metaphysics, but I see that you were a Fellow of the Cambridge Philosophical Society. My uncle, who was a great formative influence in my life, was a member of the Liverpool Literary and Philosophical Society, along with Oliver Lodge. If the math seems strange, I am 82 and my uncle lived to 95.

Cat :)
 
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Jzz

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Greetings Dr Joe! Nice to have you back. My question to you is this: “Is gravity intrinsic to matter as Newton maintained or is it innate to matter as Einstein had stated?”

What is the difference? The term intrinsic implies a property of matter that is acquired and not part of the particle, substance etc., whereas something that is innate implies that it is a property that the particle possesses as part of its integral or inherent structure.

I have often been annoyed by Einstein’s denigration of Newton and his theory of gravity by stating that Newton had advocated action at a distance as part of his gravitational theory. This is a completely false allegation. Here is what Newton had to say about AAD (Action at a distance):

"That gravity should be innate, inherent, and essential to matter, so that one body may act upon another, at a distance through a vacuum ... is to me ... an absurdity."

In fact Newton admitted that although he could not describe why gravity worked in the way that it did, he was able to explain in great detail, how it worked in the way that it did. He hoped that future generation would solve the puzzle of gravity.

As far as I am concerned Einstein merely used gravity as an explanation of itself. He used gravity to explain gravity! His theory is a thinly veiled clone of Newton’s gravity where he replaces Newton’s gravitational force with a gravitational potential. Same difference!
 
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Hi suneritz - Always good to hear these great, out-of-the box, ideas! And that's a novel use for an accelerator!

Apart from the fact that we can't break something into its constituent elements, let alone put it back together, we have a couple of inconvenient facts about physics. 1) The speed of light: Nothing with mass (so the molecules, or even sub-atomic particles if we could get to that level too) can travel faster than the speed of light in vacuum. We might be able to accelerate the particles to a fraction of the speed of light but not to the speed of light. It would still take a long time for travel. 2) Newton's laws - gravity could possibly slow the particles as they neared a target star, but it would likely not be sufficient, and they would just zoom by.

Since I don't want to end on a low note, here are some fun things related to your suggestion:

SpingLaunch: https://www.space.com/spinlaunch-first-test-flight-success

And lots of research into linear accelerators to launch payloads - mass drivers: https://en.wikipedia.org/wiki/Mass_driver
Joe,

As a spin-off that idea could you have a particle accelerator which accelerates and continuously fires metal (conducting) particles. You put second particle accelerator at L2 point near Mars so it forms a closed loop. Then it simultaneously runs a high voltage through it like powerline which would be superconducting since it’s in space temperatures. May be we could then point it at Mars and ride it like Maglev trains? Even if you have gaps in “wire” may be electrons could jump them. Probably we could start with the Moon first.

Thanks
 
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DrJoePesce

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Another question, if I may please, Dr Joe:

I have great problems with finding relative values of entropy for the singularity at the BB, and later in the development of the Universe. If the singularity has 'infinite' density/temperature et cetera I would have thought that the entropy would be very high? Yet, as the Universe expands, entropy must increase. (Assuming the Universe is a closed system). Why not BB to cold death?

Yet, we find a low degree of entropy in the Universe, with galactic structures, and stars instead of molecular clouds. And life, even, some of it projecting heat death for the Universe.

If we accept that physics breaks down as we approach t = 0, then what is the direction of entropy from the earliest moment that physics becomes valid?

Cat :)
Hi Cat – these are all great, challenging, questions! I think the main point here is the distinction between local and non-local, general, entropy. Locally we can have all sorts of situations, as long as on the whole there is no violation. And I suspect this is what is happening with the BB.

When you say “physics becomes valid” what do you mean? Physics is always valid, it’s just that the laws of physics we know and understand “break down” at the singularity because it has r=0. But that just means we have more work to do! :)
 

DrJoePesce

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A few planck lengths no prob. Some physics alters the trajectory: 1) Everything exerts gravity and is in motion enroute. An extra sunspot on AC(two) buffets some dust out later and now gravity in the system is different and it plays a mini-version of Armageddon's Lunar torque effect on the doomsday asteriod.
2) Yarkovsky Effect on the molecule. 3) Light heating's non-Yarkosky Effects. 4) Nanodust impacts. Plasma spheres the molecules pass through en route (Heliopause) might even stop the molecules cold. Subatomic particle impacts. Dust/soot collisions. Any variability of nearby stars affects the search space and state space of each molecule's trajectory. Consider space time is made of energy occasionally creating new subatomic particles and these are likely to impact the molecules eventually.H2 deeper space density is one atom every 4m^3 or something. Stuff becoming polarized in space is alot like the forces that would buffet the molecules.

My thread question is are there any moons in the Jovian system far enough away for manned exploration, from the radiation Jupiter and Io send outwards? Thx.
Hi Phillip Huggan – Welcome!

By this question do you mean far enough away from the perturbations in Jupiter’s magnetosphere caused by interaction with Io?

My planetary-science colleagues will probably jump on me, but I think so. In any case, if I were an astronaut, wherever, I would want to be within a magnetosphere because that is what protects from cosmic rays (from the Sun and elsewhere).

I am looking forward to robotic exploration of these systems, which will almost certainly be on a nearer timescale than human exploration.
 
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DrJoePesce

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Greetings Dr Joe! Nice to have you back. My question to you is this: “Is gravity intrinsic to matter as Newton maintained or is it innate to matter as Einstein had stated?”

What is the difference? The term intrinsic implies a property of matter that is acquired and not part of the particle, substance etc., whereas something that is innate implies that it is a property that the particle possesses as part of its integral or inherent structure.

I have often been annoyed by Einstein’s denigration of Newton and his theory of gravity by stating that Newton had advocated action at a distance as part of his gravitational theory. This is a completely false allegation. Here is what Newton had to say about AAD (Action at a distance):

"That gravity should be innate, inherent, and essential to matter, so that one body may act upon another, at a distance through a vacuum ... is to me ... an absurdity."

In fact Newton admitted that although he could not describe why gravity worked in the way that it did, he was able to explain in great detail, how it worked in the way that it did. He hoped that future generation would solve the puzzle of gravity.

As far as I am concerned Einstein merely used gravity as an explanation of itself. He used gravity to explain gravity! His theory is a thinly veiled clone of Newton’s gravity where he replaces Newton’s gravitational force with a gravitational potential. Same difference!
Hi Jzz – thanks! It’s good to be here with you all!

I don’t know if I personally have a take on this (although I kind of give it at the end! :) ). Other than to say:
  • Newton was fantastic, and I have a special place in my heart for him, not only because of, well, physics! But because of my Cambridge connection. Having said that, we can’t forget Einstein has two hundred years of science on Newton, person insight and intuition of both of them aside.
  • Einstein really isn’t circumventing Newton, just enhancing him. Relativity, in the low velocity, weak gravity environment which pervades most of the universe (and certainly most of our local experience) is just Newton’s laws. Einstein’s “specialness” comes in visualizing the extremes.
  • This is, I think, regardless of what gravity truly is. Personally I would say that gravity is a property of matter, so perhaps a view more Newtonian than Einsteinian.
 
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Catastrophe

"There never was a good war, or a bad peace."
Hi Dr Joe,
"When you say “physics becomes valid” what do you mean? Physics is always valid, it’s just that the laws of physics we know and understand “break down” at the singularity "
Thank you for that correction. That is, of course what I intended. Cat :) :) :)
 

Catastrophe

"There never was a good war, or a bad peace."
Hi Dr Joe, I hope you will excuse my asking a metaphysical question. I highly respect your scientific supremacy and the fact that you are a Fellow of the Cambridge Philosophical Society.

I have seen your responses to questions of time travel, and would suggest that #54 and #58 open the way to a definitive answer.

In the BLOCK model, time lines appear to suggest predetermination. At least, our access seems limited up to the moment we call 'now'. It is a non question to talk about visiting the past because we (today) were not there in the fixed time line. Thus we might possibly be able to view that 'now' in the time line (don't ask me how) but there is no way that we can interact with it or change it in any way.

I have no suggestions about visiting the 'future'. If there were to be any mechanism of accessing the time line (which seems to be prevented by the 'now' mechanism) I can only think that it 'is' equally fixed and unalterable.

The consequences of the BLOCK model are horrendous, and beyond the remit of a scientific forum. They are beyond (IMHO) our imagination.

So, the bottom line is: does this help, in any way, to clarify the possibilities of time travel. Can we surmise that time travel is a SF 'gift'. It is most unlikely as a physical possibility and, in any case, is almost certainly not open to interaction, at least as far as the 'past' is concerned.

I retain an open mind, but the BLOCK model does seem to offer substantive answers to questions of time travel. Would you agree with this? What are the viable alternatives?

Cat :)

Edit: today - I mean we (today's now) were not present in the past. Only the past we were there then - sorry for any ambiguity.
 
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Hi Phillip Huggan – Welcome!
By this question do you mean far enough away from the perturbations in Jupiter’s magnetosphere caused by interaction with Io?
Not sure the main risk is Jupiter's Van Allen belts but it is the risk I'm not too clear on. The 3 main Belts extend 75 Jupiter radiuses. The inner presumably more concentrated one better written of. I hope Enceladus meteorites have concentrated at slush floor. Triton is inert enough. I can't see how to easily hit and run a mine on Jupiter ice moons. For big Jovian moons there is Jupiter's gravity that makes tunneling through the ice a collapse hazard. And enough weathering makes extraction hard. Just to characterize meteorites on a big Ice Moon with probes is admittedly a good step. I envision going from surface spot to surface spot and each time drilling down, and getting whacked by Van Allen radiation or cosmic rays while on the surface. Maybe the smaller moons away from the belts are safe enough from Van Allen radiation to form a the base with which to prospect, is I guess the hope of my question. melting through stable ice at any Moon should provide some cosmic ray protection for temporary infrastructures, maybe no stable ice in the system.
 

DrJoePesce

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Hi Dr Joe, I hope you will excuse my asking a metaphysical question. I highly respect your scientific supremacy and the fact that you are a Fellow of the Cambridge Philosophical Society.

I have seen your responses to questions of time travel, and would suggest that #54 and #58 open the way to a definitive answer.

In the BLOCK model, time lines appear to suggest predetermination. At least, our access seems limited up to the moment we call 'now'. It is a non question to talk about visiting the past because we (today) were not there in the fixed time line. Thus we might possibly be able to view that 'now' in the time line (don't ask me how) but there is no way that we can interact with it or change it in any way.

I have no suggestions about visiting the 'future'. If there were to be any mechanism of accessing the time line (which seems to be prevented by the 'now' mechanism) I can only think that it 'is' equally fixed and unalterable.

The consequences of the BLOCK model are horrendous, and beyond the remit of a scientific forum. They are beyond (IMHO) our imagination.

So, the bottom line is: does this help, in any way, to clarify the possibilities of time travel. Can we surmise that time travel is a SF 'gift'. It is most unlikely as a physical possibility and, in any case, is almost certainly not open to interaction, at least as far as the 'past' is concerned.

I retain an open mind, but the BLOCK model does seem to offer substantive answers to questions of time travel. Would you agree with this? What are the viable alternatives?

Cat :)

Edit: today - I mean we (today's now) were not present in the past. Only the past we were there then - sorry for any ambiguity.
Hi Cat - Yes, I agree that this is all rather complicated (an understatement!), and some elements of which are not science (since they can't yet be tested). So we enter into the realm of my opinion, and I note I've been wrong many times before and will be wrong in the future (and this is one of those things I'd love to be wrong about): I think time travel - at least in the sense we all see in science fiction - is not possible.

For the past it's as you say, I think, plus the various paradoxes (though there appears to be a way out of this (see, for example: https://www.npr.org/2020/09/27/917556254/paradox-free-time-travel-is-theoretically-possible-researchers-say) And I think future travel isn't possible, because....the future hasn't happened yet.
 
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DrJoePesce

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Not sure the main risk is Jupiter's Van Allen belts but it is the risk I'm not too clear on. The 3 main Belts extend 75 Jupiter radiuses. The inner presumably more concentrated one better written of. I hope Enceladus meteorites have concentrated at slush floor. Triton is inert enough. I can't see how to easily hit and run a mine on Jupiter ice moons. For big Jovian moons there is Jupiter's gravity that makes tunneling through the ice a collapse hazard. And enough weathering makes extraction hard. Just to characterize meteorites on a big Ice Moon with probes is admittedly a good step. I envision going from surface spot to surface spot and each time drilling down, and getting whacked by Van Allen radiation or cosmic rays while on the surface. Maybe the smaller moons away from the belts are safe enough from Van Allen radiation to form a the base with which to prospect, is I guess the hope of my question. melting through stable ice at any Moon should provide some cosmic ray protection for temporary infrastructures, maybe no stable ice in the system.
I don't think I would be too worried about the Van Allen belts, but more the perturbation caused by Io, for example. Still, I think there probably isn't a big issue. And as you point out, shielding by ice would be fantastic! There are probably stable areas of ice on most of those satellites, but you also wouldn't need to tunnel in, presumably as long as you can cover your structure with ice blocks, say. Certainly a fascinating thing to think about.
 
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Since SR (Special Relativity) is in the mix....

Perhaps you have a far better handle on some of this and can help me (us).

Of course we'll use a spaceship A (with Alice) being observed from E (Earth with Ed). [I could be in error on all of these, admittedly.]

1) Ed sees Alice's clock run slower. He adjusts for the time it took for the light from her clock to reach him, and her clock is still slower.

2) Alice does the same and sees that Ed's clock is running slower.

3) When Alice and crewmates return to Earth, however, her clock will demonstrate that her travel time consumed less time (i.e. time dilation). This is consistent will all known experiments, that I'm aware. Some say this is due to a symmetry break since Alice was the one who experienced acceleration/deceleration. Is this the mainstream view?

Also, there is a math equivalence for time dilation found in length contraction, which came along shortly before Einstein's remarkable paper. But, the only known objective evidence I've ever heard that supports this as something physical has to do with the flattening of particles at CERN (or similar facility) that greatly favors length contraction over time dilation. Is there any evidence for contraction that can't be explained by time dilation that you're aware?
 

Catastrophe

"There never was a good war, or a bad peace."
Hi Dr Joe. My sincere thanks for the most informative reply, containing references within references. I apologise for straying beyond the strict realm of science but, as you are well aware, time travel is SF screaming for clarification.

I have given an answer to the grandfather paradox. By Occam's Razor, it is preferable to assume that you (present) cannot visit your own past, because 'you' are already there in a different 'now', and your future self cannot coexist with your 'then' self, as you were not there at the time. This is instead of inventing multiverses (a non word, in this context at least). Simpler than inventing multiverses, which (inventing), presumably, is open to billions of people through history - not to mention possibly other creatures, all instigating their own scenarios. Could get a bit crowded, especially for the BLOCK model. I won't mention the BLOCK problem of predetermination ;) .

Quote
There is comfort in subsuming your sense of individuality to a larger sentiment of prescription and predetermination.
.— Jia Tolentino, The New Yorker, 1 Nov. 2019
Quote

Anyway, thanks again. I shall keep my headaches to myself, at least for some considerable time to come. :) :) :)

Cat :)
 
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Hi Joe,

Another question from me. Do we know for sure what's inside black holes? We know that inside neutron stars there are neutrons. Could it be there are also neutrons inside black holes ? In this article they discuss that black holes spin close to speed of light due to conservation of momentum. May be if our sun would spin at these speed it's gravity well (or spacetime) would also be spinning as fast, trapping the light within. Can we be sure that the black holes are not just neutron stars with more spin?

Thanks
 
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I don't think I would be too worried about the Van Allen belts, but more the perturbation caused by Io, for example. Still, I think there probably isn't a big issue...
An initial skim suggests cosmic rays accelerated inwards are bad at 10M km and very bad at 2.5M km. I have a base at Moon #16 and out as okay for Van Allen radiation but still moderately dosed by synchrotron radiation from Jupiter.
A base procedure assuming some in situ abilities:
1) Manned landing at Moon #16 with RF ion engines. Take off, accelerate fast inwards using RF engines. Cut them before inner Jovian system physics disrupts them.
2) Slow down with rockets. Land on Callisto. Not differentiated from being a 3d checkerboard of rock and ice. Meteorites will have smashed through the ice cube and stuck. Over time, they will have sunk not too far; only to the underlying rock. Here lies 3x the metals of Triton harvestable.
3) Melt through the ice with lasers. Collect the meteorite fanned out brecchia pieces. Crush them, melt them, sift them. Make ice armour for the trip back. Armour the ship.
4) The rockets that landed also need to use Callisto in situ ice propellant as rocket fuel. Make rocket fuel from the ice. Make Ions. Potentially leave ion engines on surface.
5) Lift off from Callisto using rocket fuel. Then potentially leave rocket engines in orbit.
6) Either use existing RF engines, or ferried from outer Moon RF engines, to accelerate fast in the particle and plasma soup of Callisto distance (at least with micro-meteorite armour as shielding). Radiation might cease these engines but meteorite hits will certainly obliterate most rocket fuels.
7) Cut the engines. Eventually begin a slow RF ion burn landing on Moon #16 with ions, metal ore, igloo ice. Evaluate health effects of synchrotron radiation for a potential retreat outwards.
 
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