The dumb questions thread

[beero1000]

If there are two ants walking at opposite ends of a rubber band holding a steady pace and the rubber band is stretched, one might conclude that the perceived speeds have increased while the actual speeds have not. I got that. The problem is that the formula for calculating their relativistic speed isn't supposed to account for the difference.

It is a prediction of general relativity, not special relativity. Specifically, the  FLRW metric.

Maybe I'm not expressing what I'm wanting to express.
I'm not saying an object is exceeding the speed of light through space. I'm saying an object is exceeding the speed of light.

Let's go to the Wild West where two gunfighters stand back to back and begin walking away from each other and they each take off at 95% the speed of light. Neither one is exceeding the speed of light relative to the ground, but if the ground itself between them begin to stretch causing their respective distances from one another to substantially increase, then although it will still be the case that neither is traveling greater than the speed of light relative to the ground (that's still at .95c), if the ground stretching is substantial enough, then calculating their speeds relative to each other (not the ground) should yield a speed that yields an answer greater than c.

No, I think I was answering what you wanted to ask. It's just a not-so-obvious thing to really understand without going into the details of the math.

Special relativity is, well, a special case of general relativity. Specifically, it's the one where spacetime is Minkowski space, which is flat and static. In that kind of spacetime, we can have the simple notions of speed (distance and time) that can be measured without having to worry about space warping and expanding. You can imagine special relativity as being relativity on a very small 'patch' of spacetime like a map would would be of your neighborhood, whereas general relativity handles curvature like a globe - you don't have to worry too much about curvature as long as the patch you're studying is small enough, but you do have to start dealing with the curvature once that stops being the case.

In general relativity, we allow for spacetime to curve and expand and so the idea of 'speed' needs to be formalized as either 'speed through space' or 'speed between objects'. We normally think of those two as equivalent, but they no longer are if spacetime can expand and curve. Physically, the intuitive definition for speed matches the 'speed through space' idea i.e. it's what your speedometer would read. The 'speed between objects' idea becomes much further removed from your standard idea of 'speed' when space can bend and grow and would be like measuring your velocity by constantly finding the change in your distance from the sun. It's actually worse than that though, maybe it would be more like measuring your distance from shore on a boat by measuring distance along the surface of the choppy ocean. As the waves move, you can imagine your 'distance' along the water's surface would change which would give a 'velocity' even if the boat was (locally) stationary. That's the difference.

The speed of light restriction still holds for general relativity, but the restriction is on the more intuitive 'speed through space' notion. If you try to measure 'speed between objects', and factor in the expansion of the universe, there is no restriction to speeds faster than c. In fact, if you do that then even light doesn't move at c anymore.

 

[Kharakov]

Can you calculate the mass of the universe by measuring distance to the CEH (cosmological event horizon)?



tangent-
I ran across someone who said that an observer at the CEH would be time dilated till they were frozen in time due to recession velocity.... and that it was a real effect. I said "that means we are frozen in time".

Anyway, to go even more wooish, entertaining an even more logically impossible scenario, they said an individual beyond the CEH would be travelling back in time towards the beginning of the universe, so the farther we go forwards in time, the further they travel back in time. And to them, we are going back in time too...

Ohh, and the CEH keeps getting closer all the time... what do you think about time dilation due to spacetime expansion?

 

[humbleman]

Can you calculate the mass of the universe by measuring distance to the CEH (cosmological event horizon)?

Besides the reasons given above, our limit of sight can't help us to see beyond the events we see at the further perceived.

With telescopes of the 1910's, poor Albert thought the diameter of the universe was 100 million light years, using formulas based on his crapped Cosmological Constant sh*t.

Today, we can see "further" and calculations reach up to 20 billion light years diameter of the universe.

However, the last word has not be given, we don't know at all what is going on beyond our limited sight of the universe, the reason is because the universe is not showing any "horizon line". So, the smart name "cosmological event horizon" is related to what is happening in such far away view, nothing about "this is it" that is the end of that side or, beyond that you can meet 70 virgin women crazy about you.

By the way, those 70 women are indeed virgin, but are 362'976,863'594,888'713,984'301,133 years old in menopause...

 

[steve_bank]

This may be another thread, if the universe is expanding, into what?

The only thing that makes sense to me is an infinite universe that always was and a;ways will be. Otherwise you have to explain an origin and possible end.

 

[bigfield]

This may be another thread, if the universe is expanding, into what?

The universe isn't expanding; space is expanding. Space doesn't need to be expanding into anything and it doesn't necessarily have edges.

 

[Kharakov]

This may be another thread, if the universe is expanding, into what?

The other thing could be that the wavelength of all matter in the universe is becoming shorter over time as it eats up "vacuum energy". I don't think it's likely, unless something is keeping all masses proportional.

Since light doesn't alter wavelength over time, it stays the same wavelength/frequency as when it was emitted.

This makes light redshifted compared to matter, since matter's internal clock (energy level, frequency) is constantly increasing as it consumes more and more vacuum energy.

Because we use light to see distant objects, it makes them look like they are moving slower and slower as our (matter being's) clockspeed increases over time.

 

[humbleman]

This may be another thread, if the universe is expanding, into what?

The other thing could be that the wavelength of all matter in the universe is becoming shorter over time as it eats up "vacuum energy". I don't think it's likely, unless something is keeping all masses proportional.

Since light doesn't alter wavelength over time, it stays the same wavelength/frequency as when it was emitted.

This makes light redshifted compared to matter, since matter's internal clock (energy level, frequency) is constantly increasing as it consumes more and more vacuum energy.

Because we use light to see distant objects, it makes them look like they are moving slower and slower as our (matter being's) clockspeed increases over time.

Enough!

You are the perfect candidate, send you resume to the following address.

They badly need patients like you. Other patients will be happy to hear your wisdom. No salary is offered but you will have free room, free meals, and nurses taking care of you. Lots of relativists graduated and obtained their diplomas in this institution.

http://www.sehcommunity.org/

Saint Elizabeths Hospital opened in 1855 to serve individuals with mental illnesses.

 

[bigfield]

In the client-server model used on the internet, the client makes requests to the server and receives responses from it, but is unconcerned with how the server computes these responses. That is, the server is a black box.

How is this principle labelled in terms of more general systems theory (i.e. regardless of whether one refers to computers or people)?

 

[beero1000]

In the client-server model used on the internet, the client makes requests to the server and receives responses from it, but is unconcerned with how the server computes these responses. That is, the server is a black box.

How is this principle labelled in terms of more general systems theory (i.e. regardless of whether one refers to computers or people)?

I think it's still called  separation of concerns in systems engineering.

 

[Kharakov]

This may be another thread, if the universe is expanding, into what?

The other thing could be that the wavelength of all matter in the universe is becoming shorter over time as it eats up "vacuum energy". I don't think it's likely, unless something is keeping all masses proportional.

Since light doesn't alter wavelength over time, it stays the same wavelength/frequency as when it was emitted.

This makes light redshifted compared to matter, since matter's internal clock (energy level, frequency) is constantly increasing as it consumes more and more vacuum energy.

Because we use light to see distant objects, it makes them look like they are moving slower and slower as our (matter being's) clockspeed increases over time.

Enough!

I've been wondering, for the past 10 seconds or so, how to pronounce your moniker. Is it "humm blem en", "humm blem an", or "hume bleh mun"?

Saint Elizabeths Hospital opened in 1855 to serve individuals with mental illnesses.

While I don't doubt that cooking individuals with mental illness is a good idea, I've heard they have taste.

The problem is, I've heard horrible things about hospital food. So I'm sort of... on the edge.

I'd watch the documentary on it first:

 

[bigfield]

In the client-server model used on the internet, the client makes requests to the server and receives responses from it, but is unconcerned with how the server computes these responses. That is, the server is a black box.

How is this principle labelled in terms of more general systems theory (i.e. regardless of whether one refers to computers or people)?

I think it's still called  separation of concerns in systems engineering.

Much appreciated.

 

[humbleman]

The atomic clock uses the vibration frequency of the atom of Cesium to calibrate the unit of time called second.

It is known by several evidence, that everything going out from earth ground zero to outer space will suffer changes. This is a fact.

Having that the atom of Cesium will indeed suffer changes in its vibrations because is exposed to a low gravity when is inside the atomic clock in a satellite. dumb question:

Will the data of the atomic clock -due to this change of the vibration frequency of the atom of Cesium- will be ahead or behind the data of the atomic clocks on ground zero?

 

[Loren Pechtel]

The atomic clock uses the vibration frequency of the atom of Cesium to calibrate the unit of time called second.

It is known by several evidence, that everything going out from earth ground zero to outer space will suffer changes. This is a fact.

Having that the atom of Cesium will indeed suffer changes in its vibrations because is exposed to a low gravity when is inside the atomic clock in a satellite. dumb question:

Will the data of the atomic clock -due to this change of the vibration frequency of the atom of Cesium- will be ahead or behind the data of the atomic clocks on ground zero?

You still have not addressed the problem that the four positioning systems have their constellations at three different altitudes. If the culprit is zero-g why do the three constellations need different corrections?

And why do the plane flying east and the plane flying west get different results? They're in the same gravity field, the only thing that differs is the velocity (because one is going with Earth's rotation and one is going against it.)

 

[George S]

The atomic clock uses the vibration frequency of the atom of Cesium to calibrate the unit of time called second.

It is known by several evidence, that everything going out from earth ground zero to outer space will suffer changes. This is a fact.

Having that the atom of Cesium will indeed suffer changes in its vibrations because is exposed to a low gravity when is inside the atomic clock in a satellite. dumb question:

Will the data of the atomic clock -due to this change of the vibration frequency of the atom of Cesium- will be ahead or behind the data of the atomic clocks on ground zero?

More gravitational field means a less ticks. Clocks do not tick at all at the event horizon of a black hole.
So less gravitational field means, for example, that clocks on the ISS run a bit faster than those deeper in the gravity well of Earth. Both the clock on the ISS and the one the ground are perfectly accurate. Nothing has been changed in the clock. An observer (the clock) in the ISS can measure the change in energy levels in Cs 133. The photon emitted is the standard of the atomic second. A human on the ISS will have his or her biology experiencing one second per atomic second. The human on the ground has biological processes at one second per atomic second. It is when comparing these accounts that we find that they are (quite counterintuitively) different.

The clock does not "suffer changes." It always keeps perfect (local) time. If it were returned to Earth it would beat at exactly the same rate as any other Cs 133 clock.

 

[steve_bank]

This may be another thread, if the universe is expanding, into what?

The universe isn't expanding; space is expanding. Space doesn't need to be expanding into anything and it doesn't necessarily have edges.

OK, space is expanding in terms of the definition of distance, the meter? A relativistic phenomena.

 

[fast]

Is it physically possible to launch a manned craft from earths surface and travel to the moon and do another moon landing and return alive and never once in speed go faster than half the earths escape velocity at any point from launch from earth to touch down back on earth? I think the answer is yes. What say you?

 

[bigfield]

This may be another thread, if the universe is expanding, into what?

The universe isn't expanding; space is expanding. Space doesn't need to be expanding into anything and it doesn't necessarily have edges.

OK, space is expanding in terms of the definition of distance, the meter? A relativistic phenomena.

https://en.wikipedia.org/wiki/Metric_expansion_of_space

The metric expansion of space is the increase of the distance between two distant parts of the universe with time. It is an intrinsic expansion whereby the scale of space itself changes. It means that the early universe did not expand "into" anything and does not require space to exist "outside" the universe - instead space itself changed, carrying the early universe with it as it grew. This is a completely different kind of expansion than the expansions and explosions seen in daily life.

Metric expansion is a key feature of Big Bang cosmology, is modeled mathematically with the Friedmann-Lemaître-Robertson-Walker metric...

 

[steve_bank]

Thanks.

With the condition of my eyes going through text on the net is difficult.

 

[steve_bank]

Here is another one. I recently watched Space Odyssey. In a scene Dave is running inside the rotating cylinder. If he gets both feet off the surface what happens? I'd think he is in zero g with momentum from the rotation when he was in contact. Is it possible to run as depicted in the movie?

If he jumps up his momentum carries him forward and at some point he hits the surface.

 

[bigfield]

Here is another one. I recently watched Space Odyssey. In a scene Dave is running inside the rotating cylinder. If he gets both feet off the surface what happens? I'd think he is in zero g with momentum from the rotation when he was in contact. Is it possible to run as depicted in the movie?

If he jumps up his momentum carries him forward and at some point he hits the surface.

That makes sense.

If Dave jumps "straight up", he will be carried on a vector that is the sum of a tangent to the cylinder and a vector that lies on the diameter of the cylinder. This vector intersects the cylinder somewhere "ahead" of Dave. The higher he jumps, the greater the arc he traverses.

With each step, Dave is propelling himself along a tiny chord. It would feel considerably different (and require different biomechanics) than normal running since he is only accelerating while his feet are touching the ground, whereas one is always accelerating (and and down) while running in gravity.

So while one probably wouldn't run using Dave's technique, one would still be able to run in some fashion.