Consider two sound waves travelling in opposite directions between two opposite walls in a long and wide hall. As a result, standing waves form, which in reality appear to be standing, and yet, they are the result of two wave trains travelling in opposite directions. In this simple case, what appears is not what exists, but is only a resultant of a more profound reality.
The existence of troughs and crests does not imply the waves are in some places not present, but that their resultant sometimes is zero.
You can use a vacuum and use two laser beams from the same source to achieve coherence, but that is much much more difficult to achieve. A vacuum can be obtained, either by travelling sufficiently far away from the sun and earth (extremely expensive) or by using a high grade vacuum.
It’s entirely possible to use non vacuum freespace optics to entangle photons or light. Have a look at parametric down conversion for example.
There’s been a slew of quantum sensing for example - entangle the photons, send one off to the target and the other to the sensor. You don’t have to wait for (or even need a reflection) to sense the hole stealth leaves behind.
On the flip side active sensing also screams here i am! So it’s a two edge sword.
;-)
If we revert to the ether thesis, then we would not have to attribute "potentials" to a "vacuum", which is nonsense.
Besides, it is important to distinguish science and science enterprise. And furthermore intelligence/military science and civil science. Civil science serves above all to lead the citizen around at the nose;-) "Civil scientist" included;-))
In civil science ether is frowned upon, but we should ask secret service and military how far they are with ether and electromagnetic and magnetic phenomena, up to the use as weapons, EMF-weapons for example.
If we revert to the ether thesis, then we would not have to attribute "potentials" to a "vacuum", which is nonsense.
Besides, it is important to distinguish science and science enterprise. And furthermore intelligence/military science and civil science. Civil science serves above all to lead the citizen around at the nose;-) "Civil scientist" included;-))
In civil science ether is frowned upon, but we should ask secret service and military how far they are with ether and electromagnetic and magnetic phenomena, up to the use as weapons, EMF-weapons for example.
The thing about flawed or incomplete hypotheses is that we can't get to the next step by merely discarding them, if they in fact do provide some reliable explanations for observations. We need to look at what's wrong with them sometimes to discover an answer.
Classical statics and dynamics (Newtonian physics) has been indispensable to engineers for centuries. It's been used to reliably design all kinds of civil structures with reliable and repeatable results. Yet when scientists started to look closer at particle physics and radioactivity, they realized that their observations didn't line up with their predictions. Their predictions were reliably wrong.
Somehow, Einstein solved this puzzle with the theory of relativity. Now scientists could make reliable and repeatable predictions about particle physics. And, it made scientists look at cosmology with a completely new perspective, leading to many discoveries etc.
Now we're at the point where our predictions are not in accordance with observations. "Dark matter" is kind of a placeholder for a concept that can't be explained. Remember, Newtonian physics wasn't really wrong; just incomplete. We need to find out what "dark matter" is, and isn't, to get to the next level of understanding.
See video link below (4 min long) : She is so lovely and funny with a very nice voice! And challenge every scientist about his self-confidence! (video is about the tragic consequences of the last 3 years for everyone of us)
Please set video speed to 75% (or 50% but sound gets aggressive) und switch to automatic translation from german to english , in the video settings (toothwheel symbol) , in case you can't understand the german language , thanks!
The issue is mass being assigned to something with no measurable mass. It's been discovered but we don't know what it is. It has to be there or our established model is invalid. Not the same as predicting as yet undiscovered elements knowing they're there and assigning their periodic numbers right to the undiscovered final element. Those are "placeholders". What's missing is an actually accurate model that combines GR with SR. Most likely doesn't include anything remotely explainable by the idea of "Dark Matter or Energy". It isn't about unidentified substance, just plain misunderstanding of what we're observing. It needs a name? How about...we just don't know why..yet? Why conjure up a fictitious element? We might as well be a living Star Trek episode.
Two candidates for a theory of quantum gravity are loop quantum gravity and string theory, the latter of which was mentioned earlier by planet10.
So far neither of these candidates gives a complete answer to the question of quantum gravity.
Attached, is my understanding of string theory (annotation credit to system7).
So far neither of these candidates gives a complete answer to the question of quantum gravity.
Attached, is my understanding of string theory (annotation credit to system7).
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This seems like a good juncture to repeat my string theory joke!
A son asks his dad "Daddy, what is string theory?"
The dad replies "Why are you asking me such difficult questions? Come on, ask me something easier."
The son then asks "Um ok, so why does mummy get mad sometimes?"
"String theory is a theoretical framework in which the point-like, zero dimensional particles of particle physics are replaced by one-dimensional extended entities called strings..."
A son asks his dad "Daddy, what is string theory?"
The dad replies "Why are you asking me such difficult questions? Come on, ask me something easier."
The son then asks "Um ok, so why does mummy get mad sometimes?"
"String theory is a theoretical framework in which the point-like, zero dimensional particles of particle physics are replaced by one-dimensional extended entities called strings..."
There is, of course, an alternative to dark matter.
It could be there is NO missing ingredient such as dark matter, but instead the law of gravity might break down at scales larger than that of our Solar System.
Some scientists favour that alternative, and consider that our current theory of gravity breaks down on larger cosmic scales and so has to be modified.
This hypothesis is known as MOdified Newtonian Dynamics or MOND. https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics
However, dark matter has become the prevailing, accepted theory because of its ability to predict the conditions of the early universe.
P.S. An example of where the law of gravity breaks down is in the rotational speeds of galaxies. Discrepancies have been found where the outer stars in certain spiral galaxies are moving at a greater speed than the inner stars. A galaxy that was governed by normal matter alone (shown on the left in the animation) would have much lower rotational speeds in the outer regions than towards the centre, similar to the way that the planets in the Solar System behave. Instead the rotational speeds are largely radius independent (as shown on the right). The solution to that conundrum is to hypothesise the existence of a dark matter halo surrounding the galaxy.
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Sure. But the whole point is that this hypothetical concept is that it has some of the properties of mass. And of course adding it to the mix seems to make it possible to make predictions. The name is descriptive.
If we can either explain it, or refute it, then we will be making progress.
That sounds a little like relativity.
One way or another, it needs to be explained. And postulating that gravity "breaks down" at scale opens up a whole other can of worms.
No, that's actually not the point but you do a good job in revealing what is.. the arrogance of the scientific community to present it not as you say, a "hypothetical concept" but rather a material fact. That's what I find so annoying about it. There's got to be a financial incentive for the widespread acceptance of such a ridiculous notion. After all, research can't happen without funding and funding without demonstrable progress.
It should be stressed that dark matter is not yet a fact, but is still hypothetical.
Responsible scientists require to examine the implications and consequences of this particular hypothesis for the rest of the Universe and this is where dark matter shows promise.
By introducing dark matter, scientists can arrive at an entirely new picture of how structure formed in the Universe.
Modern data sets from large-scale universe structure surveys show remarkable agreement between observations and the dark matter hypothesis.
Responsible scientists require to examine the implications and consequences of this particular hypothesis for the rest of the Universe and this is where dark matter shows promise.
By introducing dark matter, scientists can arrive at an entirely new picture of how structure formed in the Universe.
Modern data sets from large-scale universe structure surveys show remarkable agreement between observations and the dark matter hypothesis.