Ask any question you want about Physics

a reply to: Arbitrageur
Q: Does the universe have an edge?

A: We don't know, it may or may not. The universe might be finite or infinite, and in the latter case it wouldn't have an edge.

it won't have an edge as such. Edge is probably a naive way to describe what should be more correctly termed, furthest reaches/points of our known universe. Or, a point where it ceases to be our universe.
Edge would mean a physical barrier. But, at this point where it ceases to be our universe is only vacuum energy or zero point energy. So there would not be any energy to create an edge as such.

Q: Is it possible the universe will collapse at some point?

Yes it is possible.
Vacuum energy or zero point energy is spent or decayed energy to the point of zero. Once, it was energy, matter, mass. If all mass breaks down to the point of zero point energy. Then there will become a point where there is actually less energy in the universe than vacuum/zero point energy. I can only see two possibilities. Either, the universe will die and flat off. Becoming a baron empty universe/space. Or, if negative pressure within the universe is created. Meaning. There is less pressure inside the universe than outside the points where it ceases to be our universe. then yes. It would collapse and hopefully to the point where another big bang happens. And it all starts again. But, there would need to be a mechanism to create the negative pressure to allow this to occur. We know black holes are very powerful. If they are pulling in vacuum/zero point energy. Then this would create the negative pressure to a cause collapse. Making collapse more of a possibility. I prefer the collapse /big bang scenario.

originally posted by: blackcrowe
Vacuum energy or zero point energy is spent or decayed energy to the point of zero.

If you read the link I provided it shows we are still ignorant about vacuum or zero point energy. However we do have a definition for it:

Zero-point energy

Zero-point energy, also called quantum vacuum zero-point energy, is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state.

Once, it was energy, matter, mass. If all mass breaks down to the point of zero point energy. Then there will become a point where there is actually less energy in the universe than vacuum/zero point energy.

There are two problems with this.

The first is that we aren't sure exactly how mass will break down, for example we don't know how stable protons are and if they will eventually decay or not, but given a long enough time scale they probably will, but there will also be black holes, which will eventually "evaporate". I suspect "vacuum energy" is not a viable idea for a decay product of baryonic decay which might decay into photons and leptons, or black hole evaporation which might result in not only massless particles but also heavier particles such as electrons, positrons, protons and antiprotons.

The second is that by definition, zero-point energy is the lowest possible energy state. Does it make sense to say the energy will go below the lowest possible state? If the energy does go lower, then it obviously wasn't the lowest possible energy state before, right?

Going below the lowest possible energy state seems like standing at the south pole on Earth and asking, "which direction is south from here?" You're already at the south pole, there's no direction you can travel to head south. The same thing applies to trying to go below the lowest possible energy state, unless I'm missing something, like maybe some temporary quantum fluctuations but those would just be temporary.

I have a friend who also favored the collapse scenario and was disappointed by the 1998 discovery that it seems less likely than before; I think this is not uncommon. But I think your scenario to try to justify why collapse might still happen is a stretch. There may be other more plausible scenarios which might result in collapse but they are somewhat speculative.

Thanks.
I did read the link.

If you read the link I provided it shows we are still ignorant about vacuum or zero point energy.

So, it doesn't make what i'm saying is actually wrong.

Zero-point energy, also called quantum vacuum zero-point energy, is the lowest possible energy that a quantum mechanical physical system may have; it is the energy of its ground state.

I agree. But i think the true ground state equals zero.

There are two problems with this.
The first is that we aren't sure exactly how mass will break down, for example we don't know how stable protons are and if they will eventually decay or not, but given a long enough time scale they probably will,

This is how i think. Eventually everything decays. It would now be at a point equal to zero. A true constant of vacuum/zero point energy. A state where it is the same everywhere, all the time.

The second is that by definition, zero-point energy is the lowest possible energy state. Does it make sense to say the energy will go below the lowest possible state? If the energy does go lower, then it obviously wasn't the lowest possible energy state before, right?

Yes. This is right. Of course.
What i'm trying to say is that eventually, there will become a time when there is less energy/matter equal to the the product that is zero point energy, which was once energy/matter. And, is now itself zero point energy and part of the constant state which we call the vacuum energy or zero point energy. Space.

hi there.... I know that Bullwinkle Moose as Mr Know-it-all, of the 'Rocky Show' would answer my query, but since your here now I will ask you.


background: I find & keep odd rocks on my hikes, I had this particular pitted heavy stone for--- I can't remember but it washed up on the beach after a particular strong 'Nor-Easter' (perhaps 35 years ago)


here are two very amateurish pics just made today....
(I was inspired after watching a PBS , re-run, show "Meteor" and I think the stone might be from outer space)





and another side of the guy:





over the years I have also found a mid sized ( about 5 1/2") Megladon tooth which I prepped for wearing as a necklace for my surfer son

I have red rocks from Sedona
I have 3 white pebbles from meteor crater in AZ
I have a mineral rock from Jerome AZ
and I have tens of other stones from places I have also been drawn to

thanks for any identification you can determine

If gravity from the moon is strong enough to create tides, why is the gravity to a human on the moon only one sixth? If the moon can tug up the oceans from that distance, why weren't the moon astronauts stuck to the moon?

a reply to: St Udio
There are some meteorite experts on ATS who could help you, but I'm not one of them.

I suggest starting a thread in the Fragile Earth forum. Here are some example threads along these lines:

Help identifying a rock.
I Might Have Found a Stony meteorite?

I could give only a guess, as I'm no expert.

originally posted by: TheLamb
If gravity from the moon is strong enough to create tides, why is the gravity to a human on the moon only one sixth? If the moon can tug up the oceans from that distance, why weren't the moon astronauts stuck to the moon?

You answered your own question about why astronauts weren't stuck to the moon, as lunar gravity is only about 1/6 that of Earth, but that's enough to cause tides.

Apparently you think gravity needs to be stronger cause tides. It doesn't need to be that strong.

Gravity from the sun is over 80 times stronger than gravity from the moon, so the strength of the gravity is not the dominant factor. If it was, the sun tides would be larger. The moon's tides are larger because the differential gravity from the near side of earth and the far side of earth is more significant with the moon than with the sun which is farther away.

Tidal mechanics are not trivial, it gets a little complicated.

a reply to: TheLamb

Ocean is really big. There is lot of water for the lunar and solar gravity to work on from the long distance. The mass of a single person is really small compared to that person´s strength. As Arb was saying, the full treatment of tides is a bit complex, but the first point is that ocean is biiiiig.

originally posted by: Arbitrageur
The Earth's surface is a 2D analogy for 3D space. Do you deny that if you travel in one direction in a plane you can end up back where you started?

If we are talking about the idea of potential 'nothing space/nothing area';

First of all we are talking about the most ultimate conception and comprehension of reality.

Why is this simple concept I am about to state so difficult for you to grasp;

Imagine if absolute nothing existed (no energy or matter or anything, no substance, no potential, no 'your definition of space', no quark soup or virtual particles, no waves, no radiation... nothing nothing nothing);

Imagine only absolutely pure nothing 'existed';

Would area/distance exist?

And would it be infinite in all directions?

originally posted by: ImaFungi
Why is this simple concept I am about to state so difficult for you to grasp;

Imagine if absolute nothing existed (no energy or matter or anything, no substance, no potential, no 'your definition of space', no quark soup or virtual particles, no waves, no radiation... nothing nothing nothing);

Imagine only absolutely pure nothing 'existed';

Would area/distance exist?

It's difficult to grasp because I live in this universe and as far as I can tell, nothing like that exists in this universe.

If I try to imagine what's outside this universe, I suppose there are many possibilities. Maybe in another universe there is such a thing as "absolute nothing with dimensions" but then you have a semantics problem because if it has dimensions is it absolute nothing?

Michio Kaku says if it has space it doesn't meet his definition of absolute nothing.

I say I'm having a hard enough time figuring out how this universe works without worrying about what's outside it, especially since nobody will ever see outside it to determine whose guess was right about what if anything is beyond it.

Imagine only absolutely pure nothing 'existed';

Would area/distance exist?

And would it be infinite in all directions?

In this pure nothing scenario. Area and distance, if any would be irrelevant. As it is a constant. The same everywhere, all the time. Here, there, up there, over there etc is all the same place too. But, it would take an observer to be able to perceive the scenario. So, in that case. It couldn't exist. But, if it did. It would be infinite because there is no time to measure.

originally posted by: blackcrowe
Imagine only absolutely pure nothing 'existed';

Would area/distance exist?

And would it be infinite in all directions?

In this pure nothing scenario. Area and distance, if any would be irrelevant. As it is a constant. The same everywhere, all the time. Here, there, up there, over there etc is all the same place too. But, it would take an observer to be able to perceive the scenario. So, in that case. It couldn't exist. But, if it did. It would be infinite because there is no time to measure.

Just the fact of having an observer there sets certain laws into play. Without distance for example I doubt you would observe much being a point of matter. Certain laws of physics need to exist to observe for example let's say there was truly a 2 dimentional plane. Nothing could live there because a digestive tract would split an animal in two.

Take this thought a bit further the moment you introduce something the area is no longer a void and new properties would emerge. Then your right back where you were was there anything there before you got there you have no way of knowing.

originally posted by: blackcrowe
Imagine only absolutely pure nothing 'existed';

Would area/distance exist?

And would it be infinite in all directions?

In this pure nothing scenario. Area and distance, if any would be irrelevant. As it is a constant. The same everywhere, all the time. Here, there, up there, over there etc is all the same place too. But, it would take an observer to be able to perceive the scenario. So, in that case. It couldn't exist. But, if it did. It would be infinite because there is no time to measure.

Imagine absolutely nothing existed (no energy or matter or anything, no substance, no potential, no 'your definition of space', no quark soup or virtual particles, no waves, no radiation... nothing nothing nothing);

Why I think infinite area of nothingness, is an unavoidable fact of reality;

Is because under the assumption of 'absolutely nothing existing' ( no energy or matter etc.);

If then a single bowling ball existed, theoretically I would have no reason to suggest that 'movement' would be an absolutely impossible physical occurrence;

(instead of a bowling ball imagine some wound up mechanical robot popped into existence with a ball in its spring loaded, timer driven, arm, if you are a stickler; or not even, it is proper of me to be more thorough as this example)

So because that is the case; I would have no reason to think that an object (which had the potential to move at all) if it were to pop up, as the only object that existed in all of reality;

I have no reason to presume, that it would not truly be able to move away, from (in the robot arm example) the point of its energetic release;

(another example would be a mechanically timer set robot finger on a gun trigger popping into existence as the only objects that exist in all of reality, popping into a realm that is purely absolute nothing.

If such is the case, is there any reasoning as to why the bullet would not truly travel away from the gun, in 'real actual distance', cover real area;

And would not that area be, pure absolute nothigness;

And would the bullet have any reason to stop?

Would the bullet not continually be really traveling a future distance from its starting point?

And does that not seem to suggest, that there is a real area, of 'nothingness', which is unavoidably existing, in relation to 'all that is somethingness';

And due to it seeming as if there is no reason the bullet would stop, does this not suggest that the area of nothing is infinite, in any incremental measurement of distance/area (besides infinitesimally)

ImaFungi.
If that nothing space could exist. As i said above. Would be a constant state. The same, everywhere, always. No distance would actually exist either. If by some chance, you could fire a bullet in there. It would be anywhere and or everywhere always.
Time wouldn't exist. So, inside that nothing space would be infinite. Within itself. If it existed.
But, the concept of it can't exist. It would take an observer to see it. And, then it wouldn't be a nothing space.
Your asking an impossible question.

Arbitrageur.
Thanks.
The links were useful.
So, now you've shattered my whole world (sarc).
If there is no collapse of the universe, and it does flat out, dies off and eventually all energy decays. At this point. Will it actually exist. And, if it doesn't. Did it ever exist?
Vacuum/ zero point energy. Would you consider it is possible to manipulate it back into energy under pressure? As, even though its value is zero. It is still something in its own right. And was everything before. Essentially.
Is vacuum energy the only true constant. The same, everywhere, all the time?
Universal expansion. How is the space being created to cause the expansion? I will offer my theory. As energy decays to the point of vacuum energy. Zero. It has a spatial quality to it. Example. 1 single grain of sand decayed to vacuum energy would create more space than we could actually contemplate as being the whole size of the universe. Maybe.
Would black holes provide enough pressure to convert vacuum energy back into an energy?
bc

a reply to: blackcrowe
Isaac Asimov, The Last Question. (pdf)

originally posted by: ImaFungi
(another example would be a mechanically timer set robot finger on a gun trigger popping into existence as the only objects that exist in all of reality, popping into a realm that is purely absolute nothing.

If such is the case, is there any reasoning as to why the bullet would not truly travel away from the gun, in 'real actual distance', cover real area;

Yes there's a reason the bullet won't go anywhere and I'm sure you can figure it out if you think about that scenario. Probably more than one reason but at least one good one. If you can't figure it out let me know.

originally posted by: blackcrowe
Time wouldn't exist. So, inside that nothing space would be infinite.

Lack of time doesn't necessarily infer infinity. A video shows time and a photograph shows a slice of that time, which is not infinite.

originally posted by: blackcrowe
Arbitrageur.
Thanks.
The links were useful.

Thanks for reading them. I'm glad you found them helpful.

So, now you've shattered my whole world

(sarc).
If there is no collapse of the universe, and it does flat out, dies off and eventually all energy decays. At this point. Will it actually exist. And, if it doesn't. Did it ever exist?

It will exist but it will be very uninteresting. However all hope is not lost. We don't like the idea of the universe dying. We no longer think the collapse is likely to occur, but we figured out another way to start over without the collapse. The idea is that a quantum fluctuation in the future uninteresting universe might spawn another big bang and another universe. Who knows if it's true? It's just an idea at this point and there are competing ideas also in search of supporting evidence. It will take a very long time for such a quantum fluctuation to occur according to this model. Here is a paper along these lines, co-authored by the physicist who appears in the opening post video:

Spontaneous Inflation and the Origin of the Arrow of Time

We suggest that spontaneous eternal inflation can provide a natural explanation for the thermodynamic arrow of time, and discuss the underlying assumptions and consequences of this view. In the absence of inflation, we argue that systems coupled to gravity usually evolve asymptotically to the vacuum, which is the only natural state in a thermodynamic sense. In the presence of a small positive vacuum energy and an appropriate inflaton field, the de Sitter vacuum is unstable to the spontaneous onset of inflation at a higher energy scale. Starting from de Sitter, inflation can increase the total entropy of the universe without bound, creating universes similar to ours in the process.

(Emphasis mine). So you might not need a collapse for a new universe to form, as it might be able to form from quantum fluctuations of an old and probably nearly dead universe.

Vacuum/ zero point energy. Would you consider it is possible to manipulate it back into energy under pressure? As, even though its value is zero.

It seems like a self-contradictory question if "pressure" is interpreted in the most common usage of the term as "positive pressure". Theory says the vacuum has the opposite of pressure, or negative pressure:

Vacuum Energy

Quantum theory of the vacuum further stipulates that the pressure of the zero-state vacuum energy is always negative

If you have a case where something is creating positive pressure, you no longer have a vacuum.

It is still something in its own right. And was everything before. Essentially.
Is vacuum energy the only true constant. The same, everywhere, all the time?

We have more questions about the vacuum than answers I think.

Universal expansion. How is the space being created to cause the expansion? I will offer my theory. As energy decays to the point of vacuum energy. Zero. It has a spatial quality to it. Example. 1 single grain of sand decayed to vacuum energy would create more space than we could actually contemplate as being the whole size of the universe. Maybe.
Would black holes provide enough pressure to convert vacuum energy back into an energy?

We have a wealth of observations so we're not completely ignorant, but we are ignorant concerning how to explain some of the observations, in particular dark matter and dark energy. We can't say with 100% certainty what dark matter is, but we have lots of ideas and we can say what it's not, with at least some confidence. Most of dark matter appears to not be black holes, or baryonic matter. Both dark matter and dark energy are considered in the lambda-CDM cosmological model but they are not presumed to be directly related in a fashion such as "Would black holes provide enough pressure to convert vacuum energy back into an energy?" which would imply some kind of direct linkage.

One reason I think that dark matter and dark energy appear not directly related is because of the apparent difference in distribution. Dark energy (which we suspect is really vacuum energy) appears to be everywhere uniformly (though more data is still coming in on this and is subject to refinement). In contrast, dark matter is very clumpy and does not appear everywhere, so I think this would be a big obstacle to drawing some kind of direct connection between them.

a reply to: Pirvonen
Thanks.
Your link didn't work. But found vid of himself telling the story.
Very thought provoking.
www.google.co.uk... e.com%2Fwatch%3Fv%3DR3U30wSAV4Q&usg=AFQjCNF_H-sCVG-YRvPNXoH4L52ej7GdRA

a reply to: Arbitrageur

Thank you.
More reading to do.

originally posted by: Arbitrageur
Yes there's a reason the bullet won't go anywhere and I'm sure you can figure it out if you think about that scenario. Probably more than one reason but at least one good one. If you can't figure it out let me know.

Im interested in hearing all the reasons you think there are which justified this response.

a reply to: ImaFungi
OK back to Michio Kaku's definitions of:
Absolute nothing = nothing, no space, no time, no equations, no properties
Vacuum = absence of matter with space, time and properties to which we ascribe equations.

As dragonridr said there mere presence of an object means you no longer have absolute nothing.
Once you have something, there must be some kind of properties which define its existence.
The closest you could come to "nothing" in our universe is "vacuum", in which case the bullet would travel (as long as the powder wasn't too close to absolute zero temperature), but the vacuum in our universe has properties, including space, time, and properties which allow chemical reactions to take place.

If you could somehow put the gun in "absolute nothing", how could any chemical reactions take place in the powder if there were no properties which defined how those reactions would proceed? How could the gun or the bullet exist?
Also, how could the bullet travel without space or time? Space and time are properties of a vacuum. They are not properties of nothing, the way Dr. Kaku defines absolute nothing.

Dr. Kaku's two definitions of "nothing"

Dr Michio Kaku is Professor of Theoretical Physics at City University, New York. He asks: “How can it be that everything comes from nothing?” His solution: “If you think about it a while, you begin to realise it all depends on how you define ‘nothing’!”2

We are then shown a huge NASA vacuum chamber, the largest in the world—the nearest we can get to a state of nothing, but which still has dimensions (‘nothing in 3D’), and through which light can pass. Prof. Kaku tells us: “I think there are two kinds of nothing. First there is something I call absolute nothing: no equations, no space, no time, no anything that the human mind can conceive of, just nothing. Then there is the vacuum which is nothing but the absence of matter.”

The host then comments: “Prof. Kaku’s version of nothing is the perfect vacuum where on the face of it there is only energy. But in a perfect vacuum, energy sometimes transforms itself temporarily and briefly into matter. It is one of these tiny explosions that might have been going on and ended up in the big bang.”