Genady
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Posts posted by Genady
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2 hours ago, geordief said:
When the twins separate ,they could do so from a nonaccelerating point in space and time.
This is how the "twins' paradox" is usually set up.
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As you were writing that post, you were an accelerating observer, according to the equivalence principle. The ISS, for example, is a nonaccelerating one. Here are all your answers.
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I think you can figure it out yourself. Hint: compare with tidal effects, which exist on Earth but not on an accelerating spacecraft.
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Here is my intuition. Let's assume that I artificially narrow myself to the range [N, N]. I.e., my range contains only one integer. Does it lower my probability to win? No, it does not. The probability is still 1/N, like that of everyone else.
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test
in The Sandbox
deleted
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13 minutes ago, Moontanman said:
fluorescent green
Hmmm... My blood is just dark green there. Not fluorescent at all.
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4 hours ago, Maartenn100 said:
as observers, we are always in the center of an expanding universe, expanding in all directions in space
This is factually incorrect. Observationally, the cosmic microwave background radiation is redshifted in one direction and blueshifted in the opposite direction. It is attributed to our peculiar motion relative to the cosmological comoving reference frame. Only after this peculiar motion is removed, the universe appears to expand isotropically.
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1 hour ago, joigus said:
AFAIK triggering of even serious form of schizophrenia only happens after environmental factors have made their appearance.
But I'm very far from being an expert here
I also am very far from being an expert, rather just a witness. In the case I've witnessed, specific environmental factor has made obvious a very serious form of schizophrenia, but then its signs could be traced back for years of misdiagnosis.
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27 minutes ago, geordief said:
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)
It depends on the symmetries of a situation. For example, a spherically symmetric case, e.g., Schwarzschild black hole, is usually visualized in 2D, i.e., temporal and radial.
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14 minutes ago, geordief said:
Because it is spacetime that is curved and not space?
Exactly.
In the spacetime, they both have curvature of about 1 lightyear radius:
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3 minutes ago, tmdarkmatter said:
But if the light coming from the star was perpendicular, the star would have the size of just a few millimetres and that is not the case. The further away we are, the smaller we see the star. At a further distance, the angle of the visible light coming from the star becomes smaller.
At the very far distance, the angle between light rays from the star becomes 0, that is the rays are just parallel to each other. Draw the picture and you will see what happens to the shadow when the rays are parallel.
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12 minutes ago, tmdarkmatter said:
How big must an object be so at a distance of the diameter of earth it is able to block the light coming from Proxima Centauri so it creates a shadow that is just big enough to cover an object of the size of 1 metre, 2 metres, 10 metres?
1 metre, 2 metres, 10 metres, assuming the shadow is perpendicular to the light ray.
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2 minutes ago, 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.
You are spoiling my question in the post right above yours ... 😉
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The main problem with the trampoline analogy is that it has nothing to do with the gravity related spacetime curvature. A curious student should ask after watching it,
"How can the tracks of a ball and of a bullet be curved so differently if that curvature arises from the geometry of space?" (MTW, Gravitation (p. 32).)
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1 minute ago, iNow said:
You are, of course, correct. We’re in violent agreement.
You seem to be saying there is a relevant difference between one’s consciousness and the functioning of that consciousness.
Do I read you correctly, and if so, I’d be curious to learn more about that distinction you seem to demarcate.
No, I am not interested in this distinction. Sorry that what I said or how I said it sounded like this distinction is of any importance to me.
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2 minutes ago, iNow said:
One might even say the amount or direction of that functioning changes
One might say whatever one wants.
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14 minutes ago, geordief said:
I think consciousnesss could be extensive in the same way as a particle extends into its field according to QFT.
This analogy doesn't work because a particle does not extend into its field in QFT, but rather it is its field when the latter is not in the ground state.
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20 minutes ago, geordief said:
I think more along the lines that your consciousness is those experiences.
There is nothing "hands off" about what I think of as consciousness.It is entirely immersive , athough there is an illusion of an "internal observer". which is just a facet of our consciousness.
This is the difference in our approach: I think that my consciousness is a symbolic reflection of my experiences. The experiences, including thoughts and concepts, are not conscious.
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1 minute ago, geordief said:
You are thinking of a coma?
So if you have an experience where "nothing could be better" (as in the oft quoted line"it was bliss that day to be alive" ) and this is followed by the depths of despair (perhaps as a result of a medical condition) your consciousness does not follow any direction?
In the former experience all your days lie ahead of you in anticipation and in the later there is no tomorrow.
Is your consciousness diminished or altered?
My consciousness records these experiences.
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11 minutes ago, iNow said:
Depends upon how one defines it. States of consciousness certainly change, when inebriated or otherwise intoxicated, sick, fatigued, dehydrated, low blood sugar, under duress, suffering a head injury, etc.
Yes, its functioning changes. And sometimes stops.
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Consciousness does not have amount or direction. It is a symbolic system of recording experiences.
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1 hour ago, Markus Hanke said:
Nowhere does it claim a ‘causative relationship’,
In spite of this, a 'causative relationship' exists operationally, i.e., we can, in principle, manipulate the source and this would affect geometry, but there is no way to manipulate geometry without manipulating the source. The 'symmetry' is broken.
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32 minutes ago, TheVat said:
no tricks
Not for you, but for me
Spoilerit was a language trick (and I learned something new), because in Russian, they are all близнецы regardless of number.
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How does a physical system evolve under acceleration?
in Relativity
Posted
It is wrong to assume that physical processes during acceleration are responsible for the time dilation. Time dilation is a geometrical rather than a physical effect. It is caused by the geometry of Minkowski spacetime.
Let me describe the "twin's paradox" when nothing happens during an "acceleration".
There is a clock located at 4 lh (light-hours) from Earth which is synchronized with the clock on Earth. Let's call this point in space, T. A ship moves with the speed 0.8c past the Earth. At the moment when a clock on the ship passes the clock on Earth, it is set to whatever is the time on Earth. Let's say, 10:00.
The ship reaches the point T in 4/0.8=5 hours in the Earth time. The clock in T, which is synchronized with the clock on Earth, shows 10:00+5=15:00 when the clock on the ship passes it. However, the clock on the ship shows at this exact point in spacetime, i.e., as the two clocks are side-by-side, 10:00+3=13:00, because the time dilation factor for the speed of 0.8c is 0.6, and thus the trip to the point T takes 5*0.6=3 hours in the ship time.
At the same exact point in spacetime, another ship passes the point T, going toward the Earth with the speed 0.8c. They grab the ship's clock and take it back to Earth. This trip back takes the same 5 hours in the Earth time and the same 3 hours in the ship time.
So, when the clock returns to Earth, the clock on Earth shows 10:00+5+5=20:00, while the returned clock shows 10:00+3+3=16:00. Done.