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If you're in the US and the jet is in Australia, you won't hear it whether it's subsonic or supersonic.
originally posted by: Nodrak
Think about a jet flying away from you at Mach 1.5, will you hear it? Will you ever hear it?
In the context of the new standard Lambda-CDM cosmology we point out confusions regarding the particle horizon, the event horizon, the ``observable universe'' and the Hubble sphere (distance at which recession velocity = c). We show that we can observe galaxies that have, and always have had, recession velocities greater than the speed of light. We explain why this does not violate special relativity and we link these concepts to observational tests.
What exotic matter? We know a few small components of dark matter, and some of it is not very exotic, like baryonic dark matter, what makes up the earth. Some is black holes. Some is likely neutrinos. But we just don't know what the vast majority of dark matter is, though we have some ideas. This is a slide a physicist posted here showing some of the ideas:
originally posted by: Exit89
Great response thank you for taking the time
If we could determine according to the dark matter map where this exotic material was, do we have the tech to see what it looks like in our reference though?
I have no idea what you mean by this, because I've never heard dark matter being described as "ejecting" anything.
I imagine sending a probe into the dark matter is not necessary. I think we are just looking at what it is ejecting a bit poorly.
You seem very confused. Maybe you're thinking of "dark energy" which has been very loosely and somewhat incorrectly described as an opposite of gravity or "anti-gravity", but that's a relatively poor and inaccurate description even for dark energy. Dark matter on the other hand, is thought to interact gravitationally with matter, explaining the rotation curves of galaxies, amove other things. You said you wanted to ask a question that was difficult to google the answer to, but explanations of what we know about dark matter and dark energy can be googled...see NASA's descriptions of them for starters.
Also i assume dark matter has the opposite effect of gravity which would make a probe very hard?
Well, sort of, but in reality, observations of planets are only in our own galaxy and the stretching of the wavelengths called "gravitational red-shifting" is rather limited for things like planets. It's been measured even on earth in the Pound-Rebka Experiment, but it's a rather small effect so it wasn't that easy to measure.
I want the readers of this to imagine sending a signal from a matter dense planet. Lets say its a flashlight. We send the signal at a certain " wavelength" but please for now just think of this as a width of a beam. As we send this beam out it expands because it enters a lesser gravitational field. Over time we have to compress and speed up this beam to view it as it was originally sent. When we are viewing planets using radio ( because the visible light spectrum stretched ) it is due to the effects of the beam going from a stronger gravity field into a lesser over time ( im sort of making this part up ).
I wouldn't call "white-holes" ridiculous, but on the other hand they lost their popularity after the 1970s when it was realized they would be unstable:
I am imagining if we turned this flashlight on from a "white-hole" ( im really sorry this is probably ridiculous ) that it would blue shift into a tiny tiny tiny wavelength before it entered our fields of our negative pressure gravity ( and then refract or dilate a bit?).
Then the article talks about a way to get around the instability problem is to say maybe white holes can be observed as "bangs", perhaps short-lived events like gamma-ray bursts. Some papers have been written along these lines, even one saying the big bang might be a gigantic white hole event, but it seems to me like "the jury is out" on those ideas. A paper hypothesized that GRB060614 might be a white hole event, but as you can see from the linked NASA article on that, NASA just says we are lacking a model to explain it. Maybe a white hole is one possibility, but further research is needed.
The idea of white holes was fashionable for a time in the 1970s. People spoke of wormholes, with a black hole on one end and a white whole on the other. Could these wormholes be tunnels in spacetime through which intrepid travelers could journey instantaneously across vast distances in the universe? But further thought caused people to realize that white holes would be extremely unstable, and hence highly unlikely to exist, in fact so unlikely that no one has talked about them much in recent decades. They are truly fringe science. So far, no astronomical source has been successfully tagged a white hole.
If you're talking about planets, again we are typically trying to look for evidence of those in our own galaxy, and planets don't have that much gravitational redshift, which you will see if you study the measurements in the pound-Rebka experiment.
In easy mode, if we were listening to a voice recording that is in a stronger gravitational field than ours it would be low octave and slow.
The closest things I'm aware of to a "negative gravitational field" is not really that at all, but dark energy has been compared to that. But what this "sort of anti-gravity" effect does is often misrepresented in the popular media, so many people hear the term "anti-gravity" and a large misunderstanding results. A good explanation is offered here by physicist Frank Heile:
So can i assume that something from a negative gravitational field would be really fast and high pitched? And can we mess with that?
The problem is that the word "anti-gravity" invokes a vision of a vehicle floating above the ground (as seen in many science fiction movies). Dark energy will not allow the development of anti-gravity floating vehicles. In fact, dark energy cannot even be added to an object so that it could repel other objects (it doesn't matter if the other object has "dark energy" in it or not).
What dark energy really does is that it causes space to repel itself. So dark energy is anti-gravity but only for space itself.
If there were no dark energy, then as the universe expands from the big bang, the rate of expansion would slow down with time since all the matter in the universe is attracting all the other matter in the universe via their mutual gravitation attraction. Gravity would not likely be able to stop and reverse the expansion of the universe, but it would definitely slow it down.
Instead we observe that the universe's rate of expansion is actually speeding up right now. Why? Because as the universe has expanded, the matter density of the universe (mass per volume) has decreased with time such that the repulsion of space pushing against itself (because of dark energy) has now overcome the attractive force of matter...
originally posted by: ThatDamnDuckAgain
a reply to: Nodrak
As a wave travels through space, it hits atoms and gets absorbed. The frequency of this wave that gets absorbed is related to the energy required to alter electron orbits. These happen in things called 'Quanta'. In math terms, thees are just whole numbers.
Is this related to Zyklotronresonanz? The resonance frequency needed to transfer energy from EM waves to free electrons in the ionosphere, for example?
originally posted by: Arbitrageur
If you're in the US and the jet is in Australia, you won't hear it whether it's subsonic or supersonic.
originally posted by: Nodrak
Think about a jet flying away from you at Mach 1.5, will you hear it? Will you ever hear it?
originally posted by: ThatDamnDuckAgain
Is this related to Zyklotronresonanz? The resonance frequency needed to transfer energy from EM waves to free electrons in the ionosphere, for example?
This is the basis for many things, including cyclotrons (microwave ovens), electron orbital distances. If you heard of china's new engine for their missiles, this is it.
That's what the physicist Frank Heile said, after explaning it's not really anti-gravity.
originally posted by: Exit89
"What dark energy really does is that it causes space to repel itself. So dark energy is anti-gravity but only for space itself."
That's not completely true. Let's say a radio wave is emitted from a source 10 light years from a neutron star. As the radio wave heads toward the neutron star, it's gravitationally blue shifted, so the wavelength shrinks more and more as it approaches the surface, then if it bounces off the surface, it's gravitationally red-shifted when leaving. Once the reflected radio wave is 10 light years away from the neutron star, assuming no other gravitational influences, the net change is wavelength is zero. It has neither shrunk nor stretched once it bounced off to the same distance away.
The one thing i know about gravity is the more of it there is the slower you accumulate events and when radio waves bounce off these things and travel long distance they expand their wavelength.
Can you find even a single example in the scientific literature where a gravitationally red-shifted electromagnetic signal originating in visible light was shifted outside the visible spectrum by gravitational red-shifting alone?
We then shrink this wavelength to see what was "redshifted" in a visible spectrum.
For starters, it's not anti-gravity. That's a dumbed down analogy used to explain the dark energy phenomenon to laymen, and even then the physicist I cited started out by explaining it's not really anti-gravity.
Why would antigravity NOT have the opposite effect?
Why would you assume when we have measurements? The whole reason we think space in the universe is expanding is because wavelengths from more distant sources are longer, and we think the expansion is accelerating due to dark energy, meaning the stretching is even more than we would expect if there was no dark energy.
If "dark energy" causes space to repel itself i think we can assume time will be condensed here
I don't know what space condensing on itself means? According to general relativity it's matter or energy that causes time dilation, not "condensed space" whatever that is supposed to mean.
considering when space condenses on itself time dilates.
That's a poor hypothesis in several respects.
Im assuming dark energy would cause anything that bounces off it to blue shift to an extreme degree and this is why we cannot visibly see the stuff.
I think what astronomers do is record the light they receive, then they can process that recorded information however they want. So they could shrink or stretch what they find, but I think more typically they would use spectroscopy to see where the spectral lines are located, which can tell them if what they see is red-shifted or blue-shifted and by how much. For cosmological observations they then convert this to a "z" number, a measurement of red-shift if positive, or of blue-shift if negative. The comparison looks like this:
If we can see light that has redshifted into radio waves, is it possible to do the opposite thing and stretch something that blue shifted ?
Arrows indicate redshift...
The value of a redshift is often denoted by the letter z, corresponding to the fractional change in wavelength (positive for redshifts, negative for blueshifts), and by the wavelength ratio 1 + z (which is >1 for redshifts,
I don't think that's a good example of the 'butterfly effect', but yes I suppose you might make the argument the signal is still there and just overwhelmed with the noise from other signals such that the signal to noise ratio makes it impossible to hear it. Looking for alien transmissions from outer space in the way SETI does tend to result in signal to noise issues, since there a lot of other sources of noise, but the signals should still reach us in the background.
originally posted by: Nodrak
Technically you will hear it as part of the noise of the environment, even if its below your detection threshold. This is effectively the basis for the saying 'butterfly effect'
The paper I linked for you in my previous post mentions this at the end of the abstract:
High sensitivity experiments have tried to prove a local Doppler effect in order to prove the expansion, but all have failed to my knowledge.
The authors go on to explain at length how the cosmological redshift is not a special relativistic Doppler redshift, even though they found some misleading literature to suggest that, such as "texts asking students to calculate the velocity of a high redshift receding galaxy using the special relativistic Doppler shift equation."
We analyze apparent magnitudes of supernovae and observationally rule out the special relativistic Doppler interpretation of cosmological redshifts at a confidence level of 23σ.
The Hubble sphere recedes as long as the deceleration parameter q = − ̈RR/ ̇R2 > −1
...
Exponential expansion, such as that found in inflation, has q = −1. Therefore the Hubble sphere is at a constant proper distance and coincident with the event horizon.
...
Firstly, objects on our event horizon do have infinite redshift.
The current distance to our particle horizon and its velocity is difficult to say due to the unknown
duration of inflation
Figure 6 shows the expected change in redshift due to cosmological acceleration or deceleration is only ∆z ∼ 10^−8 over 100 years
shows that all galaxies beyond a redshift of z = 1.46 are receding faster than the speed of light (Fig. 2). Hundreds of galaxies with z > 1.46 have been observed. The highest spectroscopic redshift observed in the Hubble deep field is z = 6.68 (Chen et al., 1999) and the Sloan digital sky survey has identified four galaxies at z > 6 (Fan et al., 2003). All of these galaxies have always been receding superluminally
a reply to: Crowfoot
the changing form like gold trading off one planck distance worth with other local elements to become lead
Atomic decay is a misnomer it is best thought of as trading through the forces of the entire atomic structure.
there is however a moment where one atomic weight of gold and one atomic weight of lead can't tell the difference between each other and such a thing in my opinion would be termed space time.