1

Physiology & Medicine / Re: Why Are Satisfying Videos Satisfying ?

« on: 20/05/2023 12:31:58 »

Ewe might enjoy videos, I don't particularly do so, I (r)am more interested in a readable text on any given subject.

2

Chemistry / Re: Does The pH of Milk Change When Heating?

« on: 15/05/2023 21:18:32 »

Milk is basically water, protein, lactose, minerals and lipids( colloidal ). I don't envisage any great ph change unless exposed to fierce heat but small changes could be expected mainly from protein degradation. PS Alancalverd, I know you were referring to BC and not me.

3

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 15/05/2023 09:56:05 »

in an expanding universe, light will be redshifted...a photon experiences time because it does have a property that can change

That is a fairly slow rate of change, not easily observable within a lab.

Another property that can change more rapidly with time is the amplitude of the electric and magnetic fields of a coherent light beam. In the absence of any measurable expansion of the local universe in the time that light takes to cross the lab, a light beam in a vacuum will keep the same amplitude, frequency and direction (ok - you need to ignore Earth's gravity too!). Since these are the main characteristics of light, the light itself is not changed by the passage of time.

Similarly, if you slow down light by putting it through glass or water, any light that managed to avoid absorption, scattering or reflection will be effectively identical to what went in, so they are unchanged by the "experience". Since there is no change, there is no experience of time (for the light itself).

4

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 14/05/2023 15:57:06 »

The key here is that it is "c" which is the important thing, not the light itself.  As far as we know, light in a vacuum travels at c.  But even if this turned out not to be the case, it would not change the importance of the speed c as an invariant speed. It would just mean that the photon is not the truly "massless" particle we now consider it to be. 

5

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 14/05/2023 08:49:12 »

Time is what separates sequential events*. A photon cannot experience sequence as it has no memory.


*an original statement, but apparently my predecessor Prof A Einstein said "time is what prevents everything from happening at once", an arguably anthroponormative definition but having the same import.

6

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 14/05/2023 00:56:17 »

Hi.

   That's quite a good answer from @Halc with very few words used.

    It's better to focus on making some sense of how light might be considered as being slowed down,  rather than to keep it at light speed and just ask if it experiences time.   But since Halc has already done one I might as well take a line or two to talk about the other.

    Suppose you don't consider time as something on a space-time diagram like that described by Halc or anything to do with an eigenvector of spacetime that has a negative eigenvalue for the metric in General relativity.  Instead just consider time as a record of change (possibly a cause or consequence of change).   Where there is change, time can be meaningfully identified and in our ordinary understanding of time we might say that change requires time to pass.
     Now in an expanding universe, light will be redshifted.  So its frequency is changing in any sensible co-ordinate system you care to use.   Just to be clear, the exact frequency it has is a frame dependant thing and we're not too interested in that.   However, the fact that the frequency is changing remains true in every co-ordinate system that you could (sensibly) choose.  So the changing of frequency is a frame independent characteristic that the photon has.   It's a short step to suggest that a photon experiences time because it does have a property that can change.   We can always use that to construct a notion of time (the photon was redder, so that will be defined as "later" in the lifetime of the photon etc.)

   I'm not going to fill in the details, it's just an alternative approach.  Time is complicated and modelled in various ways.   In an expanding universe you've got an easy option available for how you might get time to emerge for a photon. 

Best Wishes.

7

Physics, Astronomy & Cosmology / Re: Can Light Experience 'Time'

« on: 13/05/2023 17:56:25 »

Light travels well fast that at it's top speed it does not perceive time.....weird eh ?

Well, besides the point that subatomic things don't have 'experience', but that's probably not what's being asked.

If you were to slow light down, would the photons then experience time?

Only a time-like worldline defines a meaningful frame in which it has a temporal length. That means that a clock following that time-like line will log a certain amount of time. This is independent of any chosen frame.
This cannot happen for a space-like wordline nor a light-like worldline, which is what is followed by all things lacking proper mass.

All that jarjgon aside, if you slowed a photon down, it wouldn't be a photon, but the path taken by this slowed-down not-photon thing would indeed have a frame-independent temporal length, so in that sense, yes, it would experience time.

For instance, while light slows down in glass or some other medium with a refractive index, a photon does not. A photon at best can be said to be absorbed by the glass, briefly exciting some atom which in very short order emits a new photon in the same direction as the old one. It isn't the same photon, and it is a mistake to give a photon classic properties like that when it is a quantum thing, not a classical thing.
But bottom line is that you can have say a pipe in a square U shape with fast water running through it. You shine a light pulse from the side and it goes through the straight bottom part of the pipe to the other side. If the water flows fast enough, the light pulse will slow effectively to a stop relative to the pipe and will 'experience' as much time as does the pipe.

8

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/

9

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.

10

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.

11

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.

12

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..

13

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.

14

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

15

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?

16

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)

17

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.

18

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.

19

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.

20

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?