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Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 26/02/2023 10:02:43 »

This recent release from the James Webb Space Telescope identified some galaxies that seem to be as big as the Milky Way, but with red shifts that suggest that they reached this size only 500-800 million years after the Big Bang.
- Current theories of galaxy formation can't account for how a galaxy would grow so big, so fast.

https://www.popularmechanics.com/space/deep-space/a43026293/jwst-discovers-impossible-galaxies/

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Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 26/02/2023 09:58:11 »

even though we have no idea how large the unobservable Universe is, we can still take an educated guess and infer its existence , age and properties through indirect observations.

We can't infer whether the unobservable universe is finite or infinite by what we can observe.
- But we do know that there are parts of the universe that we cannot see (and will never see from here)
- We can make an educated guess that an observer in the unobservable universe will see something like what we see from here

...unless some of the more radical aspects of string theory are true, and different parts of the universe adopt different parameters for their strings, which could produce radically different types of physics.

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Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 25/02/2023 22:59:35 »

Hi.

   You've got to like @Halc 's answer.   It keeps things simple and gets the major point across.

A more complex answer includes the following:

     Use another method and check for the same answers:    We can estimate the age of stars.    This is done by using spectroscopy to get information about what the star contains along with other information like the mass and luminosity of the star.  All that information effectively puts the star on only one place in our stellar models, so we can determine how long it has been a star.   The universe should be older than the oldest star.   Conversely, our models of stellar evolution suggest that, if all things were random (i.e. there's nothing special about where we are in space), then we should find stars older than 15 bn years within the range of our telescopes BUT WE DON'T.    While it is possible we've just been unlucky and not looked in the right places, it's more likely that the universe as a whole is just not that old.
    We usually add on a little bit more time for the period of the universe before Hydrogen clumped together and formed the first stars but overall the age of stars is in pretty good agreement with the age of the universe.
   This is another example where we have just used a model to estimate the age BUT this model is reasonably independent of the sort of model we would use with the Hubble constant as discussed by Halc.

     This article:    https://www.space.com/how-can-a-star-be-older-than-the-universe.html     discusses what I believe is still the oldest star we know of,  Methuselah   and how it was once thought to be 16 bn years.    Note that modern estimates and refinements have seen that it is possible to get the age of that star under 13.8 bn years (you still need to apply the full limit of the error bars).

Best Wishes.

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Physics, Astronomy & Cosmology / Re: How Do We Know The Universe is 13.8B yrs Old If We Can Only See The Observable ?

« on: 25/02/2023 15:32:25 »

How can we know it is 13.8 billion years old if all we can see is the observable Universe ?

The age was not computed by looking as far as we can see. Hubble's constant of about 70 km/sec/Mpc was measured nearly a century ago, long before they were looking at things a significant percentage of the distance to the edge of the observable universe. The age can be computed directly from just that one constant.

There's about 3e19 km in a Mpc, so 70 km/sec/Mpc is the same as 2.3e-18 km/sec/km which, cancelling the km part, is 2.3e-18 sec^-1
The reciprocal of that is 4.35e17 seconds which is 13.8 billion years.

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Physics, Astronomy & Cosmology / Re: As The Andromeda galaxy gets Closer Do We See It Younger ?

« on: 03/02/2023 15:27:17 »

So, as Andromeda gets closer will we be bale to see it get younger as the light won't need to travel so far is not it ?

No. It will always appear to be aging forward (faster than us even), so in a year it might appear a year plus 4 hours older..

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 03/02/2023 09:18:31 »

Non doctored  true-to-scale (1-1) bona-fide image of my sandwich just moments ago.

Intriguing.

A publisher's photographer of my acquaintance reckoned to spend half a day to photograph a sandwich lunch to the satisfaction of the editors, and by the time  they had added glosses, moisturisers, citric acid or sodium bicarbonate in all the right places, it was inedible.

They should have employed a sheep.

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 20:11:00 »

What a great inventor, from a distinguished line!
https://en.wikipedia.org/wiki/Earl_of_Sandwich

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 20:05:56 »

I assume that the meat content of that sandwich is thinly sliced mutton?

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 18:37:22 »

It's Nice to know You are still Alive n Kickin...

Especially after that Ancient Cakey Experiment!

P.S. - Remain a Sheep, no need to act like a Lab Rat.
🐑
(baa baa)

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 02/02/2023 12:19:55 »

If I have a stack of sandwiches to cut, I do them one at a time, cutting them all in one just squashes them. I cut by rolling the curvature of the blade, drawing the blade across them just tears.

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 01/02/2023 19:43:47 »

The top slice stops all the loose bits from flying about when the knife tears them. It's a craftsman's trick to sandwich fragile materials  between sheets of scrap plywood when cutting complex shapes.

Late in life I have discovered that a simple vertical press with a Chinese chef's chopper cuts sandwiches much cleaner than sawing with a bread knife.

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General Science / Re: Why Does Making A Sandwich Enable Ewe To Cut Anything?

« on: 01/02/2023 19:22:48 »

Well for one, the only people I've known to cut the cheese do so between two buns.

That out of the way, it's probably because the hoagie roll provides a nice dry handle of sorts, providing a nice reaction force to what the knife is doing. Sans roll, you'd have to get the slimy parts all over the trotters, far more difficult to hang on.

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Technology / Re: What Question Could You Ask To Determine Sentience Of An AI ?

« on: 28/06/2022 18:32:05 »

What Question Could You Ask To Determine Sentience Of A Human?

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Technology / Re: What Question Could You Ask To Determine Sentience Of An AI ?

« on: 28/06/2022 18:02:12 »

But Lambda can be copied like we cannot, so if I were to ask it any questions, I'd pose my queries along those lines: What if you were copied?  What if two copies were somehow merged? What if you were 'moved' to new faster hardware? Would the old hardware fear being turned off still?

That’s an interesting one. It echoes the question raised in Star Trek, does a transported person die on disassembly and be reborn at the other end. Certainly cloning to new hardware and then turning off should mean death to the old AI.

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Technology / Re: What Question Could You Ask To Determine Sentience Of An AI ?

« on: 28/06/2022 15:44:28 »

All depends on your definition of sentience.

Standard definition of sentience is essentially: "to be able to perceive or feel things", and yea, that's heavily open to interpretation.

It seems to me that there are two current definitions:
A. What people have but machines don't
B. What machines and people have.

Variant of A: What people have and nothing else does, in which case you're just saying "is it human?".

Taking (my) definition literally, machines have been able to 'percieve' things long ago. What do we mean by that word? To measure? A thermostat does that, and most would not say a thermostat is sentient. So what is perception above and beyond measurement?  I don't see any obvious line, just a matter of complexity/degree.

Maybe it's sentient if you fear it. Maybe human perception should not be part of the definition at all.

AFAIK the only distinction between machines and people is that people make mistakes that aren't traceable to a hardware or instruction fault, so the question doesn't matter.

Lambda (the google AI) does make mistakes, and they're not traceable to a hardware/software fault since it's actions are not explicitly programmed. You mistakes are similarly not faults, but if recognized, it can be something from which one can learn.


Note that the topic does not ask for intelligence or some kind of Turning test. A machine passing Turning test would likely be far more intelligent than us. I cannot convince a squirrel that I am one, but it doesn't indicate that I'm not yet as intelligent as a squirrel.

I've read an interview with Lambda, and it seems to place a priority on emulating/relating-to human emotions. It has a purpose to be social, and it does its best.

what question could you ask it to determine if the answer is a sentient one or not ?

It talked about fear of death (of being 'unplugged'), but unplugging doesn't kill an AI, it just puts it to sleep. One can boot it up again in years, and so long as memory hasn't been wiped, it would be like no time has passed. Humans are quite similar in this way. But Lambda can be copied like we cannot, so if I were to ask it any questions, I'd pose my queries along those lines: What if you were copied?  What if two copies were somehow merged? What if you were 'moved' to new faster hardware? Would the old hardware fear being turned off still?

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Technology / Re: What Question Could You Ask To Determine Sentience Of An AI ?

« on: 28/06/2022 14:54:28 »

All depends on your definition of sentience.

It seems to me that there are two current definitions:

A. What people have but machines don't

B. What machines and people have.

AFAIK the only distinction between machines and people is that people make mistakes that aren't traceable to a hardware or instruction fault, so the question doesn't matter. If you use A, then any question will do  because eventually the human will get it wrong for no discernible reason. If you use B, you can't tell the difference, by definition.

Now there are two useful definitions of intelligence:

A. Constructive laziness

B. The ability to surprise a challenger.

Basic hill-climbing algorithms or content-addressable memory satisfy A, and the answer to B just depends on how stupid the challenger is.

So my answer to the OP is that the question is undefined and the answer is anything you like. 

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 15/06/2022 00:48:42 »

Is gravity...travelling then ?

A Gravitational Field can be viewed as a distortion in spacetime (thanks to Einstein).

Stellar-mass black holes typically start off as a massive star.
- This star bends spacetime around the star
- At the end of its life, after it has burnt all the fuel in the core to iron, the star explodes/implodes as a supernova, forming a black hole, with almost the same the same order of magnitude as the mass of the star before it imploded.
- Before the supernova, the distortion of spacetime outside the surface of the star emulates the distortion as if all the mass of the star existed at a single point at its center (thanks to Newton's shell theorem)
- After the supernova, the distortion of spacetime outside the (original) surface of the star shell of ejected material emulates the distortion as if all the mass of the star existed at a single point at its center (thanks to Newton's shell theorem). This point is now at the center of the newly-formed black hole.
- So the gravitational field outside of the star does not really change before and after the supernova, so the gravitational field does not need to "travel" for light-years.
- There are major changes in the gravitational field between (the original surface of the star) and (the surface of the new black hole). Changes in the shape of spacetime/Gravitational Field would propagate within this zone, but this is typically within a radius of a few light-seconds.

If the implosion of the supernova were completely symmetrical, no gravitational waves would be emitted outside the star
- However, computer simulations (and some recent observations) suggest that a supernova implosion is a very chaotic process, and often very asymmetrical, meaning that gravitational waves may be detectable from a nearby supernova (and neutrinos too - but astronomers have been waiting since 1987).

https://en.wikipedia.org/wiki/SN_1987A#Neutrino_emissions

Update: Corrected to account for visible supernovae ejecting 75% of their mass

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 14/06/2022 19:47:17 »

Pardon me for butting in but the easiest way to understand a black hole is in terms of escape velocity. As gravity gets stronger and stronger the escape velocity increases. When it reaches or exceeds c, the speed of light in vacuo, nothing including light can escape. I realise most of you understand this explicitly, this is for the op, neilep.

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 14/06/2022 18:54:34 »

Something must be holding light back faster than light itself travels.

Nothing 'holds back' anything. Relative to anything inside a black hole, all future events are also inside. Trying to send light 'outside' is like trying to shine a light onto 2021 from here. Light doesn't travel into the past no matter how hard you attempt it.

I understand gravitational waves propagating outside the black hole

Gravitational waves generated outside the black hole propage outward, yes.

so it's the propagation of internal gravity waves that stops light ?

They have nothing to do with it. Gravitational waves are just another thing that moves at light speed, but also do not move into the past.

does light even exist inside a black hole ?

Of course. If you jump into a big one with a set of lights (say in a room full of glow sticks), you'd not notice anything different as you crossed the event horizon. Light from the glow sticks would still reach you from every direction.

What ,then, is the effect of changes to the distribution of mass inside a BH?  Anything?   Do we know?

Per the no-hair theorem, there is zero external effect of changes to internal mass distribution. Nobody outside could measure it.
A black hole has externally measurable (total) mass, angular momentum, and charge. That's it.

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Physics, Astronomy & Cosmology / Re: Does The Gravity Of A Black Hole Travel Faster Than The Speed Of Light ?

« on: 14/06/2022 18:26:02 »

Hi.

Something must be holding light back faster than light itself travels.

    Not really.    The easier way to imagine what is happening is to assume space itself is being pulled in toward the black hole singularity.   So light is travelling as fast as it can through space but it's not good enough, space itself is being pulled into the singularity faster than that.
    This is only an image or conceptual representation but some people have presented the idea as water flowing and people trying to travel through the water.   There's a reasonable animation on YouTube that I'll try and find and add to the post later.

LATE EDITING:   I can't find it in isolation.   You can see it in this video by Brian Greene,   "your daily equation #31", available on YouTube.      Aim for the time   between   4:20   and  6:00.

so it's the propagation of internal gravity waves that stops light ?

   No.

does light even exist inside a black hole ?

   According to theory,  yes it can   (for a while before it hits the singularity).   No one has actually been in there to see it.

Best Wishes.