Yes and no.
Closer in a closed flow system true
But an open pipe blowing on the grass no
The Speed Of Light ??
- Thread starter billt460
- Start date
Closer in a closed flow system true
But an open pipe blowing on the grass no
MolaKule
Staff member
My comments were based on the assumption of Closed Systems.
As most logically are.
My 2nd grader mind still cannot get past something about this topic.....for those who are experts, please forgive me.
How can we measure great distances? With a reasonable degree of certainty?
What I mean is:
Radar or sonar right? We send out a thing, and a thing comes back, the TIME is measured, and boom we know where something is, and how far.
Well when some thing is super far, like 3 million light years away......it would seem to me (stupid me) that it would take a bunch of time to get that data. somewhere in the 3 million years range, which I will add is a hurdle.
I have a mild understanding of Trig, as it applies to long range shooting, but I still have to have a reference on the reticle size, and a size of target to accurately gauge distance. When something is supposed to be 3 million lys away, I just dont see how we can come to a conclusion about distance.
For all we know, our neighbor, Andromeda, which is 2.5 million light years away, was eaten by by Galactus yesterday, but we would never see it.
I have yet to find a resource that will turn the switch on, for me on this one.
How can we measure great distances? With a reasonable degree of certainty?
What I mean is:
Radar or sonar right? We send out a thing, and a thing comes back, the TIME is measured, and boom we know where something is, and how far.
Well when some thing is super far, like 3 million light years away......it would seem to me (stupid me) that it would take a bunch of time to get that data. somewhere in the 3 million years range, which I will add is a hurdle.
I have a mild understanding of Trig, as it applies to long range shooting, but I still have to have a reference on the reticle size, and a size of target to accurately gauge distance. When something is supposed to be 3 million lys away, I just dont see how we can come to a conclusion about distance.
For all we know, our neighbor, Andromeda, which is 2.5 million light years away, was eaten by by Galactus yesterday, but we would never see it.
I have yet to find a resource that will turn the switch on, for me on this one.
We measure the distance of galaxies by their red shift or in some cases there are astronomical bodies that are considered "standard candles" which have a relatively fixed brightness so we can measure distance by their brightness as perceived by us. Measure really means estimate in these cases.
Another hard to grasp subject in all of this are black holes. A "black hole" in black, empty space? How can you have a "hole" inside an empty vacuum in the nothingness empty space? Where do they lead to? What has to happen in order to cause them?
If they form from a collapsed star that has basically run out of fuel, and no longer exists, where does all of this supposed incalculable, tremendous gravity come from, that turns everything into "spaghetti" that gets pulled into its grasp?
While there are lots of theories, I don't think any of this stuff has been positively answered.
If they form from a collapsed star that has basically run out of fuel, and no longer exists, where does all of this supposed incalculable, tremendous gravity come from, that turns everything into "spaghetti" that gets pulled into its grasp?
While there are lots of theories, I don't think any of this stuff has been positively answered.
Certainly no expert. I remember something about the crunching of light colors. Similar to how sound changes for race cars depending on if they're coming towards or away from you. Think they called it Dobbler shift.
Yes, we are looking at stars that are millions of years older by the time their light reaches us.
Just last night I read, thanks to the data algorithms that now send me Relativity articles, that if we observed an object going the near speed of light, we'd observe a rotated object. https://www.space.com/science/a-spa...-rotated-special-relativity-experiment-proves
Black hoes aren't black and they aren't holes, there is an immense amount of matter in them. The name is more a figure a speech because light can't escape but that doesn't mean they are completely invisible because the accretion disc of matter falling in to them produces light.
Also space isn't empty just mostly empty compared to what we think of as a vacuum and that's a whole other subject.
I highly suggest you spend an hour on this incredible lecture. One of my favorites. Of course, attending the lectures in person is better, but just the same.
Black Holes and Spinoffs KIPAC lecture at Stanford. See you at the event horizon!
I have been thinking about deep space deep time gravity effects. While a planet or star can not obtain speeds greater than the speed of light, the entire cosmos as far as we can determine, is expanding, and the further objects are from us, the faster they are moving away from us.
So, if we are moving away from some very distant point at a very fast speed, and very distant objects such as planets, stars, and galaxies very far on the other side of said point are moving away from said point, so that the total combined speeds are greater than the speed of light, and gravity effects from very distant objects acting on us travel at the speed of light, then the gravity effects from said very distant objects should never reach us? Or is the effects of gravity from said very distant objects not related to the speed said objects were moving away from us when said gravity effects originated from said very distant objects?
This ^ is actually a very important thing to figure out properly, so we know what those effects are and how they have and are and will effect us.
Or, can even said very distant objects not travel greater than the speed of light with respect to us? If the cosmos is infinite, and everything is expanding, doesn't that in itself say that at some distance from us, objects are moving at speeds with respect to us that are greater than the speed of light?
Very deep space very deep time opens up posabilities of forces acting on our local objects in very interesting ways, that actually may require some very deep thinking to totally understand what has, is, and will happen.
So, if we are moving away from some very distant point at a very fast speed, and very distant objects such as planets, stars, and galaxies very far on the other side of said point are moving away from said point, so that the total combined speeds are greater than the speed of light, and gravity effects from very distant objects acting on us travel at the speed of light, then the gravity effects from said very distant objects should never reach us? Or is the effects of gravity from said very distant objects not related to the speed said objects were moving away from us when said gravity effects originated from said very distant objects?
This ^ is actually a very important thing to figure out properly, so we know what those effects are and how they have and are and will effect us.
Or, can even said very distant objects not travel greater than the speed of light with respect to us? If the cosmos is infinite, and everything is expanding, doesn't that in itself say that at some distance from us, objects are moving at speeds with respect to us that are greater than the speed of light?
Very deep space very deep time opens up posabilities of forces acting on our local objects in very interesting ways, that actually may require some very deep thinking to totally understand what has, is, and will happen.
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Yes, and no.
Gravity is more an artifact of the curvature in space-time created by the mass of the black hole, so, yes, gravity from the black hole exists outside of the black hole, but it didn’t have to “escape” anything.
Black hole is really a misnomer, and I wish it wasn’t used in popular culture.
What we are talking about is a singularity. An object, with mass, that is real, and exists, but it’s generally not “black” because there is a very energetic accretion disk (a structure like the rings of Saturn) where matter is falling inward towards it. That matter is really hot, and so, it gives off visible light. We can see where the black hole is - and we can see the effect on matter nearby, but we just can’t see “inside” it.
The inward falling matter always ends up as a disk - it’s a consequence of the conservation of angular momentum. Same reason that all of the planets (remember, Pluto isn’t a planet any more) in our solar system are in the same plane - they were once part of an accretion disk.
The gravity from the black hole is the same as the gravity of anything else of the same mass.
Swchartzchild was one of the first to solve Einstein’s equations, and realize that this bizarre thing - an object from which light can’t escape - was one of the possible solutions. Like many new ideas - it was not widely accepted because it was fantastic, and it defied common sense. Not until decades later when astronomers observed things that could only be explained by a singularity was he vindicated.
Here’s the interesting bit about them - the Schwartschild radius defines the “edge” from which light can’t escape, but it is proportional to the mass. Just the mass. But the volume of a sphere (the shape of that radius in space) is a function of R to the third power. R cubed. Twice the mass - 8 times the volume. 100 times the mass - a million times the volume. So, as a black hole of a given mass grows, it gets less and less dense.
Still can’t see inside it because light can’t escape, but bigger means a LOT less dense.
So, at the center of our galaxy is a black hole, with a mass about 4 million times that of our sun. It is also less dense than many stars or other celestial objects.
https://en.wikipedia.org/wiki/Schwarzschild_radius#Supermassive_black_hole
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If light is made up of photons, and photons have no mass, how can they be effected by gravity? Assuming it is gravity that prevents light from escaping from a black hole 
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Radar doesn’t work in Astronomy, beyond the distance of the moon or perhaps Venus - because the beam becomes so faint as it spreads out that it just doesn’t have enough “brightness” to see the reflection. We know our own distance from the sun through careful radar measurements of our distance to Venus and by observation of Venus as it goes behind the sun (known as an occultation).
So, how do we tell interstellar distance?
It’s a fascinating story.
For relatively nearby objects, like stars out to about few hundred light years (which has been updated to about 10,000 light years with more accurate measuring tools), we use parallax. How much does the object shift against the background as a result of our orbit around the sun. Look at a star relative to the rest of them, and we can see some that move relative to that background as we swing to the other side of the sun. Our orbit is about 92 million miles, which astronomers call an “Astronomical Unit” or AU. We choose that because it is the base of a right triangle. We can see the angle of the vertex (the shift in position) and now, we do a bit or trigonometry using AU, which we know precisely (as mentioned above)
The distance of a star that shifts by one second, is about 3.2 light years, or one Parallax-Second - PARSEC. Parsecs are what Astronomers use to discuss distance.
Ok, so, how about objects that are farther?
The first big breakthrough was from Sir Edwin Hubble.
First - We knew that certain stars, known as Cepheid variables (because they were first seen in the Constellation Cepheus, the Whale) vary in luminosity. And the period of that variation is proportional to their luminosity. So, they became “standard candles” - we knew how bright they were by timing the period of their oscillations in luminosity.
When we know the absolute brightness, we can tell the distance by how bright it appears. Light spreads out, uniformly, from something like a star, so, the farther away, the more dim it appears.
Next, we knew that stars had emission and absorption spectra. That is, that the light in the star, when separated out, had very clear lines in the spectra that were the result of hydrogen emissions. Now, those emission spectral lines are exact, and they are the result of a quantum effect of electron excitation and emission of that radiation. The energy levels don’t vary so the spectra don’t vary in the absolute.
All stars have hydrogen, so, we can see those lines. Here is where the Doppler effect comes in - if those lines are shifted to a lower frequency (red shifted), then that star is receding from us. If those lines are shifter to a higher frequency (blue shifted) then that star is moving towards us.
Others had predicted that the universe could be expanding (again, the result of Einstein’s work) but Hubble was the first to see it - the farther an object was from us - the more the lines were red shifted. It was a direct correlation, built of of measurement of the red shifted and fixing distance with standard candles.
It became known as Hubble’s Law - and it firmly established that the universe was expanding.
We’ve since developed other techniques, but that’s why Hubble (edit) should have won the Noble prize and why we named that telescope after him. Astronomy wasn’t considered eligible for the prize in Physics in his lifetime, a travesty because he changed our view of the universe.
Before Hubble, we thought that was only one galaxy, and that the fuzzy objects we could see were “nebulae” - but Hubble proved that they were actually distant galaxies, equal in size, or larger, than our own. Minds were blown as the result of measuring distances accurately and correlating them with red shifts.
We’ve since refined the “Hubble Constant” and gotten a better handle on the exact relationship, but the Law, and the relationship, are firmly established.
https://en.wikipedia.org/wiki/Hubble's_law
https://en.wikipedia.org/wiki/Cosmic_distance_ladder#Parallax
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Because, as I mentioned above, gravity is simply an artifact of mass that shows up as curvature in space-time.If light is made up of photons, and photons have no mass, how can they be affected by gravity? Assuming it is gravity that prevents light from escaping from a black hole
So space itself curves, and photons follow the curve. Easy-peezy.
This has been borne out through hundreds of observations of “gravitational lensing”.
We look out in space and see two objects that are identical - well, the light from this object passed by an intermediate, big object, like a galaxy, and the galaxy bent the light, so, we are seeing the object directly, and at the same time, the object as the light from it was “bent” by the curvature in space.
Identical images, from the same source, bent by curvature in space.
https://en.wikipedia.org/wiki/Gravitational_lens
I’m sending you a book, Bill - Stephen Hawking’s “A brief history of time” should arrive in a couple days. It’s not a simple read, but it’s readable, and you don’t need complex math to understand it.
dnewton3
Staff member
Oh my. This reminded me of a conversation I had a long time ago on another forum about how the acceleration of gravity is counteracted ...
It was a LONG, ARDUOUS, PAINFUL endeavor. Simple high-school physics escapes most folks.
F=MA. You cannot have a force without acceleration.
This is the best explanation I have ever heard.
PARSEC? I heard that once in StarWars. I guess Hans Solo was not a complete idiot.
Isnt their an issue of accuracy with this? Lets face it, those stars that are 100 million light years away are likely not there anymore.....and we are just waiting to observe their death, although it happened long ago perhaps. "we"have really not been able to observe the data you spoke of, for an "extended" period of time.......Dont stars get brighter and dimmer as they make their change from a whatever dwarf to a different whatever dwarf? Honest question of course Captain.
That’s not how they work, though.
Gravity is curvature in space caused by mass.
Fuel or not, the mass exists. So, the curvature exists.
In some cases, that curvature is steep enough to cause objects to be shredded.
The gravity isn’t incalculable, it’s easily calculated. Newton gave us the formula.
F=Gm1*m2/R(squared).
When R gets really small, like it does near a small mass black hole, F can get quite big.
But, as explained in my other post, that R of the event horizon can be quite large, and so, you wouldn’t feel those tidal forces if, for example, you crossed over the event horizon (Schwartzchild radius) of the black hole at the center of the galaxy.
You might not even know it happened.
Their are accuracy issues, but they are parts per million when it comes to distance.
Very small.
And there have been millions of observations and recalculation, so the data for distance is quite good.
The calculation of the Hubble constant has seen some argument back and forth, on the order of 10%.
Which has profound consequences for predicting the ultimate fate of the universe.
But that uncertainty has zero effect on daily life here on Earth.
