andrew s

Lets keep it simple. Following Einstein,  time is what a clock measure and keeps everything  from happening  at once. Space is what a rulers measure and stops everything being in the same place.

No clock no time, no ruler no space and no clocks or rulers no space time.

Regards Andrew 

I will refrain from trying to debunk the misunderstanding about light, photons and time etc. Life is too short and I have flies to catch using the Mr Miyagi chop stick method.

1 hour ago, Moonshed said:

Hi Jim,

I would agree with you in that all fields are an intrinsic part of the fabric of the universe. I can only think of one place where they may not exist, inside a black hole.

Cheers

Keith

They are thought to exist inside a black hole. Depending on the size of the hole you could pass the event horizon without noticing anything untoward.  

It is belived that black holes can have charge as well as mass and spin. So at least the EM field and the gravitational field exist.

Regards Andrew 

1 hour ago, AndrewRrrrrr said:

isn't it that a pair of particles is created, one inside the event horizon and the other outside. they cannot get back together so the one on the outside "becomes" real and the mass of the BH becomes smaller. anyway we digress.  

Yes that's the pop science model the man himself gave. However,  you won't find it in his published peer reviewed papers.

The issue I was pointing out in your initial post on this was the energy came from the mass of the black hole not the vaccum. Maybe I miss understood. 

Regards Andrew 

2 hours ago, 900SL said:

A lot of modern physics sounds like nonsense, it has to be said.

 

Virtual this, imaginary that, negative energy etc. I know this fits the observations, but my guess is somebody is having a right laugh here.

The issue is these are pop science terms, often used by serious scientists,  to try to make modern physics approachable to those without the mathematical background for the real thing.

For example "virtual" this and that normally stand for particular elements in an perturbative expansion of the equations of QFT. They are not "real" any more than the terms in the expansion of sin(x) are real.

Energy can be negative depending on where you decide to put the zero point. For gravity its typically set at zero an infinite distance from a mass. If you have a test mass at infinity and move it towards a real mass it gains negative energy!

However,  energy is bounded from below as if not atoms would not be stable and we would be nothingness.

Regards Andrew 

7 minutes ago, saac said:

Here's a question for those who are better informed.  With respect to fields - electromagnetic field, gravitational fields etc.  Are these fields present throughout space or could there be regions (or time) where they are absent?  My common thinking is that they are present throughout, part of the fabric of the universe. 

Jim 

Yes, in quantum field theories QFT they extend throughout all space and time. In these theories there are creation and annihilation operators that add or remove excitations.

Once all excitations have been removed you can go no further and get the vaccum state. 

GR is somewhat different as it a classical theory defined on all of spacetime. But yes is the short answer.

Regards Andrew 

16 minutes ago, vlaiv said:

Yes, that is why we have mayonnaise.

I'm serious .

There is an effect that is explained by this called Casimir effect (https://en.wikipedia.org/wiki/Casimir_effect)

In order to understand this effect - we must use virtual particles popping in and out of existence.

It turns out that this effect is responsible for Mayo not behaving like liquid and keeping its shape.

 

This is still a much debated topic. It can be explained perfectly well by other models. For example van der Waals forces. 

See her for an example 

https://www.physicsforums.com/threads/jaffes-take-on-casimir-force.68169/

Regards Andrew 

1 minute ago, Sunshine said:

I wish i could explain to the extent in the documentary, im trying to wuote a renowned physicist but my knowledge is stretched to its limits.

Just relax and conserve it.😊 Regards Andrew 

2 minutes ago, saac said:

Cheers Keith, I was really commenting on your reference to Andrew S comment in your previous post 

 “Nothing by definition doesn't look like anything.”

I was trying to be clever by saying well if by definition nothing doesn't look like anything, and anything having a quality, then by extension the look of nothing also has a quality, that being the absence of anything. Exactly what that quality is - I have no idea  

Jim 

 

One must be careful not to mistake the thing for a representation of the thing.

 Nothingness (say empty space) could be represented as awash with quantum fields or a canvas rendered in deepest black. We can in various ways see the representation (mathematical equations or paint) even if not the thing in itself. 

Come on Plato time for you to step up with your forms.

😊 such fun.

Regards Andrew 

8 minutes ago, AndrewRrrrrr said:

isn't this the vacuum energy that is everywhere in the Universe? spontaneous creation and subsequent anihilation of particle/antiparticle pairs results in no net change to the vacuum energy. and it's what allows Hawkings theory that black holes evaporate 

Not quite even if one accepts this view on vacum energy. Hawking's radiation creates real particles with the energy for them taken from the gravitational energy of the black hole.

Regards Andrew 

It seems to me we are all using "nothing" or "nothingness" to mean differt things.

Is it empty space,  a state of consciousness or whatever floats your boat. 

Not only that "looks like" is also being interpreted in different ways.

Linguistic philosophers would be pulling their hair out. Not necessarily a bad thing in my book.

To steal their mantra it depends what you mean by...

No wonder I abandoned philosophy as mostly worthless.

Regards Andrew 

Nothing by definition doesn't look like anything. 

Regards Andrew 

12 hours ago, jetstream said:

This is interesting to me can you explain it further? Do all stars in an image bloat?

The image of a star formed by a telescope is not a point but a diffraction pattern created by the optics of the telescope.  It's called the point spread function.  It's central bit is similar to a gaussian function. The longer you expose the more the wings of the function get above the noise so the apparant diameter of the star increases.  Star bloat.  

Atmospheric seeing can also spread out the image as can wind gusts. 

Regards Andrew 

For any reasonable system the damping due to the inertia of the mount/telescope system should put any drive induced blurring well below the seeing psf.

Regards Andrew 

There are many types of interferometer.  If you mean the Zygo type used by OO then they have some info on there site.

In general the shorter wave length gives a more detailed picture so green is better than red. There are some subtle issues in their use for example how any off axis illumination is accounted for but they should give a fair picture of an optics quantity if not deliberately played. 

Other methods tend to be more subjective and depend more on the skill of the observer (and their prejudice).

Regards Andrew 

As @vlaiv said dark matter has a normal positive gravitational effect.

In  GR the simplest explanation of dark energy is the Lamda in Lamda CMD. That is a very small residual curvature of space time.

As we don't have a theory of quantum gravity it is difficult to relate "vacuum " energy and dark energy.  Attempts to do give a miss match by 100s of orders of magnitude. 

Regards Andrew 

38 minutes ago, JeremyS said:

Poring over the Takahashi catalogue, probably 

Wash your mouth out. Regards Andrew 

1 hour ago, Peter Drew said:

I made 8" Schmidt cameras with invar cages in the late 1970's.  Where were you Andrew?     🙂

Penniless.  Regards Andrew 

The BAA have a post https://britastro.org/forums/topic/8-celestron-schmidt-film-camera that the British Antarctic Survey are giving away an 8" Schmidt Camera.

Oh how I dreamed of having one in my youth. The precursors to the RASA line they are now obsolete but what engineering with invar cage to keep focus and magnetic curved plate holder.

You can keep your Takahashi toys 😊 this was the real deal.

Regards Andrew 

Hi @vlaiv, interesting idea. Have you worked out the effective torque?  That might be an issue for slewing. Regards Andrew 

12 minutes ago, ollypenrice said:

So this is from an unguided, driven Dob? Give that man a medal.

I hope mine won't be the only reply.

Olly

Indeed brilliant and I am not normally one to comment on images unless they are outstanding.  Regards Andrew 

I have a simple rule. I respect and enjoy those who put the subject first and themselves second.

The beauty is in the topic no matter what that might be not the presenter. 

Regards Andrew 

I have started up loading my data into the AAVSO exoplanet database where NASA imports the data into its Exoplanet Watch database. I had not realised this until I discovered my data there. They analyse the data and if they deem it ok use it to update the planets emphasises. My data is the last point on the right.

Regards Andrew 

2 minutes ago, saac said:

At that moment of realising would we just disappear in a puff of blue smoke. 

Jim 

I think therefore I'm not. 🤐

Regards Andrew 

I think we must have a common or at least very similar perception in that our mental models of the world are congruent.  If not then how do we communicate and create our rich culture and technology. 

When misaligned we identify mental illnesses and pathological behaviour. 

What astonishes me is our lack of access, via introspection,  to our metal processes. Maybe it has to be like that for our sanity. 

Regards Andrew 

19 minutes ago, saac said:

I think that must be where I left my car keys  

Jim 

I think it more likely it's where all socks were initially paired up correctly - before they became fermions. 

Regards Andrew