While I have you, how does a rotating universe work with general relativity? Doesn’t most of it have to move much faster than light?
Correct, given the size of the observable Universe, most of it will move much faster than light. However, this is okay. The only problem is if you can transfer information faster than light. A rotation like this does not actually transfer any information from one patch to the other.
Here is another example of a system that moves faster than light: take a laser pointer and point it to a faraway screen. Since this is a hypothetical situation, we can put the screen as far as we like, say 1 lightyear away. Rotate your body quickly, sweeping this laser across a wide arc. The “dot” on the screen will then move across the screen much faster than light. However, this is allowed as the dot does not actually carry any information from its previous position to its new position.
But we can’t see the dot on the screen moving until 2 years have passed. Will we actually see it moving in a quick circle? And doesn’t, say, Neptune carry any information with it as it moves around earth in its daily orbit?
That’s right, but we not seeing it doesn’t mean it’s not there. If you really want to, just wait 2 years to see it.
Yes, 2 years after you did the motion you will see the dot arc in a quick circle.
Yes, Neptune does carry information as it moves around the Earth. That’s why Neptune will never move faster than light. The reason our laser spot can move so fast is because we “multiplied” the speed of our hand rotating by a large amount due to the spot at the distance being constrained to move at the same angular velocity as our hand. There is no such constraint for Neptune.
I welcome YOUR implied willingness to get specific… and i wonder when exactly you plan to start.
I was unaware of Tycho’s work on comets… and i am still wondering when you will explain why it even matters.
You present yourself as already having some kind of professionally based encyclopedic knowledge of the period and issues involved…
…and yet i get the distinct impression that you are somewhat uncomfortable with the hole Tycho dug for himself, and so you hold back on details until absolutely cornered to do so.
While, on the other hand, my not being an astronomy academic, I have to plunge in to find the details of a given sub-topic to figure out what exactly you arent telling us.
And I find your record of forced reveals is a rather awkward pattern for you:
1] you expressly made it sound like the Heliocentrists were the ones to propose MASSIVE stars… when in fact, the complaint comes from the geocentrist camp!
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you left out the part where the geocentrist enlist the NON-Science argument that “massive stars” are just “too hard to believe”.
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Now, at last, in an effort to shore up the science “cred” for the geocentrists, you introduce Tycho’s comet studies. But…
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But… in keeping with your cryptic manner, you still havent explained how geocentrists (who were ultimately incorrect about the fictional nature of heliocentrism) … used Science BETTER than Galileo (who was ultimately right about the fictional nature of geocentrism).
Just to clarify my meaning in my comment about comets:
You mention the comets like they are some kind of clincher. I suppose they can be… but for what?
Im pretty sure you arent intending to argue that Galileo would disagree that the movement of comets refutes certain kinds of geocentric axioms.
But isnt comet research of the time using maths first developed by the heliocentrists?
What SCIENCE do the geocentrists bring to bear TO PROVE GEOCENTRISM other than “massive stars are too difficult to accept”?
Then wouldn’t relativity be unable to accommodate a non-rotating earth, because Neptune, being 4 light-hours away, would have to move faster than light to make a circuit in 24 hours?
I did here
This was to counter your demand that Tycho should do experiments to look for crystal spheres. He wouldn’t, as he is opposed to it.
You seem to have the impression that I care at all about defending Tycho. I don’t. The thing I care about is to show that back then the heliocentrists do not have a scientific claim that heliocentrism is absolutely true.
You already agreed to it:
So from my point of view there is no more reason to engage with you. I have no more interest in this line of posts. Let me enjoy my conversation with @John_Harshman. Unlike you he actually brought up good points and does not think he is well versed in areas in which he does not have expertise in.
Neptune, in this reference frame, will still be moving slower than light. But, light in this reference frame will not move at c~300000000 m/s. Remember, light only moves at c~300000000 m/s for local observers, i.e. observers that are sitting right next to it when it passes. The coordinate speed of light that is measured by the rotating observer can be anything.
Again with the unscientific language. Where does “absolutely true” come from? How is this a standard at all?
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I think this is the language they used back then: either a theory is true or false. They don’t give confidence levels quantitatively.
What do you mean by that? Would it not be moving more than 24 light-hours in 24 hours? Suppose two spaceships are sitting near Neptune’s orbit, stationary (from the perspective of the non-rotating earth frame). As Neptune passes by, one of them pastes a message onto it. And as Neptune passes by, the other one reads it. Wasn’t that sending a message faster than light?
I don’t know what that means. I thought no observer could measure a speed of light other than c.
No observer could measure that the local speed of light is other than c. In other words, no observer can measure the speed of light to be other than c if it is measuring the speed of a light beam that is very close to it.
The speed of a light beam faraway can be measured to be anything! For example, close to a black hole light beams will appear to stop (as seen from Earth). In this case the speed of those light beams is 0 instead of c. This speed is referred to as the coordinate speed of light in contrast to the local speed of light.
From the point of view of a rotating observer, Neptune will be moving faster than c, but slower than the coordinate speed of light. Thus, Neptune will not be moving faster than light in the frame of the rotating observer.
What do you mean by “rotating observer”? I believe we’re talking about a frame in which the observer on earth isn’t rotating. How does one see a light beam stop? How does one see a light beam at all unless it comes directly at you? Or is this light beam giving off photons that come in our direction, as if it were a luminous object?
I asked the two-stationary-spaceship question in an attempt to clarify. If you don’t like Neptune, consider two stationary spaceships in the orbital path (the 24-hour circle) of Alpha Centauri, which travels 24 light-years in 24 hours. That’s a very fast transfer of information.
We’re talking about the same thing. An observer that sees itself as not rotating on Earth, is in reality rotating - i.e. they measure all those forces that correspond to rotation such as the coriolis force.
We’re talking theoretically right now, as we have never seen the event horizon of a black hole yet (about to change in short order c.f. the Event Horizon Telescope). If you mathematically compute what happens to the coordinate speed of light close to a black hole, it will stop. It’s just a way for me to give an example of the large deviations from c the coordinate speed of light can take.
Much like the case with Neptune, from the point of view of the rotating observer (the person standing on Earth - who again, sees the Earth as non-rotating), Alpha Centauri is moving faster than c, but not faster than the coordinate speed of light. No transfer of information faster than c occurs here.
From the point of view of the spaceships, Alpha Centauri is not even moving faster than c as it passes them, and so no transfer of information faster than c occurs.
What do you mean by “in reality”? Are you saying there’s a privileged frame of reference?
Still don’t understand what “coordinate speed” means.
What about from the point of view of the stationary (in that frame) space-ships, who pass notes by pasting them to Alpha Centauri? How is their point of view different from that of the observer on earth, since they’re all stationary in the same frame of reference?
Then you couldn’t reasonably criticize Galileo for picking one of his only two options. His claim that the earth moves is nothing more than a choice of the better supported of two alternatives, that it moves or doesn’t move.
While it is impossible to notice that you are in a uniformly moving frame, it is possible to notice that you are in a rotating frame. This is because only when you are in a rotating frame do you feel forces such as the coriolis force.
Hmm, think about it as speed of light if you measure the speed of a beam of light far away. There is a more technical explanation of this, but I think this provides a good intuition. Only light beams that are right next to you will have speed c, light beams faraway can take whatever speed they want.
As I mentioned in my last post,
I can criticize him for affirming one of these two options. The best thing to do is say that there is not enough evidence to distinguish between the two theories. This is the same case today with string theory vs loop quantum gravity, two of the most prominent contemporary quantum gravity theories. There is not enough evidence yet to distinguish between them, and I would say that someone who affirms that String Theory is correct while Loop Quantum Gravity is wrong does so without evidence - and thus not using science.
So there is a privileged frame of reference, or at least anti-privileged frames. The person who think’s he’s stationary in a rotating frame is wrong. The earth is really, truly rotating, and general relativity cannot accommodate a frame of reference in which it isn’t. That’s what you seem to be saying now.
How would you measure such a thing?
No you can’t. You have introduced a scenario in which there are only two options, and it’s a feature of there being only two options that one of them must be accepted. That’s what “two options” means. You are now trying to introduce a third option, uncertainty, which you explicitly rejected when you said “this is the language they used back then”.
GR, and in fact even Newtonian physics could, in the expense of additional forces such as the coriolis force. Note that in GR, coriolis force is as real a force as gravitational acceleration (i.e. the 9.8 m/s^2 we feel on Earth). So if one claims that coriolis is just a “fake” force, then so is gravitational acceleration. I suppose it is a philosophical question to say whether
By their interaction with other things, e.g. if it light up a cloud of dust in space.
No! What I meant by “this is the language they used back then” was that they don’t say “My confidence for heliocentrism is at 5 sigma”. Unlike modern scientists, who would not say something is “absolutely true”, they are more comfortable in saying that something is definitely true. The option of saying “We don’t know yet” is of course available. It’s always available. This was my point this entire thread…
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