physics / maths

[Xamonas Chegwé]

You weren't "a bit right and a bit wrong" - you claimed clocks should run faster on Earth - you had it completely backwards!

I was exactly a bit right and a bit wrong. Unlike you, I pointed out that a faster moving clock runs slower.
YOU had it completely backwards !

However, I didn't know that the gravitational effects were great enough to cancel that out, and make the space clock run faster. And neither did you. You got your reasoning completely wrong. And I quote :

Change the relative velocities of two objects and their relative velocities through time change - this is real - clocks run slower on Earth than in geostationary satellites and this has to be constantly adjusted for.

No mention of gravity, the real reason why clocks run slower on Earth.
You've obviously read that clocks run slower on Earth, remembered that fact parrot fashion, but without understanding the reason why. I'm glad I've been able to help you.
I would have thought that thanks were in order, but never mind.

By the way, your attempt to gloss over getting it wrong, as in

And the gravitational effects are still relativity.

is a bit pathetic.
You never mentioned the gravitational effect till I enlightened you, so don't pretend that you knew it.

I should have known better than to respond to anything you write.

[Hermit]

Negative numbers don't actually exist either (or when did you last have minus 6 kg of cheese in your fridge?).

I'm not too sure about the negative numbers bit. We had a frost of about minus three a few nights ago.

Course you wouldn't get those in Newcastle. But you might dive to minus ten metres above sea level.

What is -1°C on the Kelvin scale? And what is ten metres below sea level? Yes, those are a matter of difference or distance. The difference between boiling point and absolute zero is not -373.16°K. It's 373.16°K. The difference between sea level and 10 metres below it is not -10m. It's 10m.

[JimC]

Negative numbers don't actually exist either (or when did you last have minus 6 kg of cheese in your fridge?).

I'm not too sure about the negative numbers bit. We had a frost of about minus three a few nights ago.

Course you wouldn't get those in Newcastle. But you might dive to minus ten metres above sea level.

What is -1°C on the Kelvin scale? And what is ten metres below sea level? Yes, those are a matter of difference or distance. The difference between boiling point and absolute zero is not -373.16°K. It's 373.16°K. The difference between sea level and 10 metres below it is not -10m. It's 10m.

It depends on how you wish to define "difference". If you decide on a scalar version of the word, then 10m is all that needs to be said. However, if you wish to convey extra information, using a vector approach, then +10m or -10m communicates the direction of the move you made going from A to B.

Also, scales such as celsius are indeed arbitrary, but no less valid for that. -1 degree C conveys an unambiguous piece of information, and so is pragmatically useful. It is true that the Kelvin scale cannot have negative numbers in principle, but that is not true of all fundamental quantities in physics: negative energy is all the go for cosmologists these days...

[Hermit]

Negative numbers don't actually exist either (or when did you last have minus 6 kg of cheese in your fridge?).

I'm not too sure about the negative numbers bit. We had a frost of about minus three a few nights ago.

Course you wouldn't get those in Newcastle. But you might dive to minus ten metres above sea level.

What is -1°C on the Kelvin scale? And what is ten metres below sea level? Yes, those are a matter of difference or distance. The difference between boiling point and absolute zero is not -373.16°K. It's 373.16°K. The difference between sea level and 10 metres below it is not -10m. It's 10m.

It depends on how you wish to define "difference". If you decide on a scalar version of the word, then 10m is all that needs to be said. However, if you wish to convey extra information, using a vector approach, then +10m or -10m communicates the direction of the move you made going from A to B.

Also, scales such as celsius are indeed arbitrary, but no less valid for that. -1 degree C conveys an unambiguous piece of information, and so is pragmatically useful. It is true that the Kelvin scale cannot have negative numbers in principle, but that is not true of all fundamental quantities in physics: negative energy is all the go for cosmologists these days...

Yes indeed, but vectors are dependent on a starting point we decide on, aren't they? I'm not familiar with negative energy, but I suspect some sort of convention along the lines of agreeing on terms on a semantic basis more than any other. A bit like alternating electric currents or magnetic polarity.

In short, I reject 'negative' as existing in an ontological sense, while I acknowledge that it can be useful in functional terms. Not wanting to talk on behalf of Nellikin, I nevertheless think she may have the same point in mind.

[mistermack]

I'm with Jim I think.
Maybe the distinction is that while only positives EXIST, negatives HAPPEN.

But events are just as real as objects. They just involve the dimension of time.

Take the example of the Kelvin scale. At any temperature above 1degK, you can have a CHANGE of + or - 1 degree. A real event. It's not just a change of 1 degree.

Same with the diving example. At sea level, a change of minus 10 metres is a real event, and not the same as plus 10 metres, which would involve getting out of the water.

[JimC]

Vectors do indeed depend on a stated starting point, although a "free-floating" vector can a useful in some contexts...

In one dimension (such as "up-down" or "left-right" a vector has a magnitude and a direction, usually expressed in terms of + and -

I contend that the set of negative numbers exists in a broad universe of mathematical possibilities and concepts. If we descend into the smaller realm of the actual physical universe, the labels may not apply in an obvious way such as "delivery pf 13 sheep for Pappa". Certainly, in physics equations where a quadratic leads to a positive and negative value for entities such as time and mass, we usually discard the negative solution as being without concrete meaning...

But sometimes, a gem is revealed from seemingly meaningless mathematics... Dirac's prediction of the positron springs to mind...

[Hermit]

I contend that the set of negative numbers exists in a broad universe of mathematical possibilities and concepts. If we descend into the smaller realm of the actual physical universe, the labels may not apply in an obvious way such as "delivery pf 13 sheep for Pappa".

Totally agreed, and I think that is the point Nellikin was making.

[mistermack]

Another thought about negatives is that it seems to be the case that the more discoveries are made, the more it seems that every positive has a corresponding negative, somewhere in the universe.

Matter has antimatter etc.

Take a bowl of five oranges, add an orange. That's +1 orange for the bowl, and -1 for the shopping bag.

If the temperature in the room rises, the same amount of heat is taken from somewhere.
Looking at it that way, there must be a hell of a lot of negative matter and energy somewhere.
So perhaps somewhere in the universe, the 6kg of cheese in the fridge is balanced by 6kg of antimatter.

[surreptitious57]

The energy level of the Universe
is zero which means it has in absolute
terms none : now this may on the face of
it seems an absurd statement to make : but
when you examine the symmetry of it it makes a
great deal of sense : all the positive energy of matter
is balanced out by all the negative energy of gravity : but
where this may falter however is with dark energy which is a
complete unknown other than it exists and is causing galaxies to
expand from each other beyond light speed : it also is a problem at
the singularity of a black hole where all known laws of physics and maths
are rendered meaningless : but as it stands with what is actually known then
it is true that the total energy level of the entire Universe is currently set at zero