Ask any question you want about Physics

originally posted by: Arbitrageur

originally posted by: AdmiralTriceratops
So, with regard to my Big Bang theory question, does Physics suggest that the inflation to the current size of the universe was instantaneous?

No. The most popular model suggests that inflation was very fast right after the big bang, then it slowed down, and then it sped up due to dark energy. At 6 minutes in this video George Smoot shows and explains a graphic illustration showing how we think it happened and he explains some of the research leading to these conclusions:

George Smoot-Design of the Universe

There's a low resolution version on youtube but there's a lot of detail in the high resolution video that it helps to be able to see.

you refer to Alan Guth expansion theory I take it.

Why do you think expansion right after that initial stage slowed but then picked up? What was the turning point between slowest expansion rate and when it started to accelerate again?

thanks

D0

originally posted by: darkorange
you refer to Alan Guth expansion theory I take it.

I wouldn't say that. I refer to the ΛCDM model, with Guth's inflation added to it, so it's a much broader model than just inflation.

Why do you think expansion right after that initial stage slowed but then picked up? What was the turning point between slowest expansion rate and when it started to accelerate again?

I am aware of no such turning point. The model calls for two phases:

1. Inflation (this is the Guth-Linde-Steinhardt contribution) which lasted for a tiny fraction of a second after the big bang
2. Dark energy related metric expansion of space (this was discovered in 1998 and is part of the ΛCDM model, where the cosmological constant "Λ" determines the rate of expansion).

When I said the expansion slowed down what I really meant was that inflation stopped. Dark energy is still something of a mystery but it's probably been at work since the very beginning, though it's kind of like if your car is going 1 kph and you accelerate 10% it's going 1.1 kph, and that 0.1 kph increase in speed doesn't seem like much, but the same 10% acceleration from 100kph is 10kph which seems like a lot more. This is why the shape of the universe expansion graph at the top of the TED page for Smoot's talk I linked to has a wastebasket shape that is pretty flat until it starts curving out to the right...it was accelerating the whole time but later accelerations are more noticeable:

That gives a general idea of the expansion profile versus time, first from inflation on the left and then from dark energy which you can see is at work the whole time but becomes more noticeable on the right, though I don't see any "turning point" other than the end of inflation.

originally posted by: Arbitrageur

originally posted by: darkorange
you refer to Alan Guth expansion theory I take it.

I wouldn't say that. I refer to the ΛCDM model, with Guth's inflation added to it, so it's a much broader model than just inflation.

Why do you think expansion right after that initial stage slowed but then picked up? What was the turning point between slowest expansion rate and when it started to accelerate again?

I am aware of no such turning point. The model calls for two phases:

1. Inflation (this is the Guth-Linde-Steinhardt contribution) which lasted for a tiny fraction of a second after the big bang
2. Dark energy related metric expansion of space (this was discovered in 1998 and is part of the ΛCDM model, where the cosmological constant "Λ" determines the rate of expansion).

When I said the expansion slowed down what I really meant was that inflation stopped. Dark energy is still something of a mystery but it's probably been at work since the very beginning, though it's kind of like if your car is going 1 kph and you accelerate 10% it's going 1.1 kph, and that 0.1 kph increase in speed doesn't seem like much, but the same 10% acceleration from 100kph is 10kph which seems like a lot more. This is why the shape of the universe expansion graph at the top of the TED page for Smoot's talk I linked to has a wastebasket shape that is pretty flat until it starts curving out to the right...it was accelerating the whole time but later accelerations are more noticeable. The acceleration plot would look different on a logarithmic scale, which might better show how there was acceleration in the early universe as well. You just don't see it in Smoot's graphic because the scale he used isn't logarithmic, in fact it's probably not to exact scale but just gives a general idea of the expansion profile versus time, first from inflation and then from dark energy.

Thanks

The reason I asked is that few times here members are expressed the notion space-time expansion accelerates? With that said, are you aware of this notion?


D0.

originally posted by: darkorange
The reason I asked is that few times here members are expressed the notion space-time expansion accelerates? With that said, are you aware of this notion?

You quoted me talking about it and then ask me if I'm aware of it? That's the 1998 discovery I referred to here:

"2. Dark energy related metric expansion of space (this was discovered in 1998 and is part of the ΛCDM model, where the cosmological constant "Λ" determines the rate of expansion"

Without the cosmological constant and before 1998 it was thought the expansion wasn't accelerating, but after several studies since 1998 confirmed the 1998 discovery, we are pretty sure the expansion really is accelerating.

originally posted by: Arbitrageur

originally posted by: darkorange
The reason I asked is that few times here members are expressed the notion space-time expansion accelerates? With that said, are you aware of this notion?

You quoted me talking about it and then ask me if I'm aware of it? That's the 1998 discovery I referred to here:

"2. Dark energy related metric expansion of space (this was discovered in 1998 and is part of the ΛCDM model, where the cosmological constant "Λ" determines the rate of expansion"

Without the cosmological constant and before 1998 it was thought the expansion wasn't accelerating, but after several studies since 1998 confirmed the 1998 discovery, we are pretty sure the expansion really is accelerating.

would you take on prediction? Is space-time going to expand forever or will meet 'resistance'?


D0.

a reply to: darkorange
I know that if I floor the gas pedal of my car, wind resistance and other factors stop the acceleration at some point and I reach a maximum speed.

With the expansion of the universe accelerating, I don't know of anything like that which is going to counteract the accelerating expansion, so lacking anything to counteract it, the logical prediction would be it will continue to accelerate.

However confidence in this prediction isn't as high as it would be for topics where we understand our models a lot better. We don't really understand dark energy and that ΛCDM model involves dark energy. It's a topic where we still have a lot to learn.

originally posted by: Arbitrageur
a reply to: darkorange
I know that if I floor the gas pedal of my car, wind resistance and other factors stop the acceleration at some point and I reach a maximum speed.

With the expansion of the universe accelerating, I don't know of anything like that which is going to counteract the accelerating expansion, so lacking anything to counteract it, the logical prediction would be it will continue to accelerate.

However confidence in this prediction isn't as high as it would be for topics where we understand our models a lot better. We don't really understand dark energy and that ΛCDM model involves dark energy. It's a topic where we still have a lot to learn.

"Wind resistance'" that is what I am asking about. is there a resistance to cosmos from what it expands into? If ther is then entropy would find escapades punching black holes to bleed excess energy/pressure? No?



D0.

a reply to: darkorange

Space has always expanded even since the beginning and has continued to accelarate. This is kind of counter intuitive in the beginning things were closer together.the further apart they get the more space that is created increasing the rate of expansion.

Since we see over and over people trying to grasp the universe I think it's time to look at the begining.In the normal general relativity picture of things, the moment of creation produced not only space, but time; the two are incredibly intermixed, after all. To Einstein, talking about what happened before the Big Bang is just as nonsensical as asking what happens if you travel north of the North Pole. logic dictates we have two possibilities for the universe The universe had some sort of beginning, in which case we're left with the very unsettling problem how it began. Or The universe has been around forever, in which case there's literally an infinite amount of history, both before and after us.

Obviously both these scenarios create a huge problem we get either how did it begin, or how can it not have a beginning. So we have a couple of models I'll only stick to the ones we haven't ruled out like we did with oscillating universe. if we were to somehow start with a small bubble of a universe, two things could happen. If it were large enough, it would undergo exponential growth or expansion. Of it was to small collapse. What caused it quantum tunneling like radiation escaping a nucleus it shouldn't be able to escape the others but it does. So imagine a universe poping into another like Bubles being formed. But then quantum mechanics throws is another twist even if the universe has zero size one can pop in to it. What is something with no size nothing! This can only be caused by the universe itself bunking of you will at its smallest scales we call it vacuum energy.

The next is the universe have birth to itself I like to think of this as a time traveleling universe. Means when the universe was created it existed in the future and the past. Stephen Hawkins goes into this in his book the beginning of time.basically it States to me isn't restricted to just two directions either forward or backward. And is called imaginary time think of it as time without a boundry meaning no restrictions on how it must behave, this would be determined with the big bang. but also time didn't have to travel in just one direction when created. so time itself is literally a loop and the past and the present and the future all exist now . This is also where the idea of a multiverse comes from. This leads to all kinds of weird possibilities. But with this the question becomes how was time created and not how was the universe created.

But with all of this what existed before the big bang absolutely nothing.

originally posted by: darkorange
"Wind resistance'" that is what I am asking about. is there a resistance to cosmos from what it expands into?

Referring to my previous answer about what the universe is expanding into, if the universe is infinite it's not expanding into anything. If it's finite there could be a boundary of some sort but the question can't be answered scientifically because we've never observed any such boundary and therefore can't say anything about it. If the inside of our universe has space-time and outside our universe, there's a lack of space-time or anything else, it may provide no resistance at all. You could guess any properties you want for what's beyond our universe if there is such a thing, but if there's no way to ever make observations to confirm or reject any of the guesses, then the guesses aren't meaningful, or as Ned Wright put it in his cosmology faq, it's not a profitable thing to think about.

If ther is then entropy would find escapades punching black holes to bleed excess energy/pressure? No?

I'm not sure what you mean by this, but if I understand your question correctly, this isn't like accelerating a particle THROUGH space, where it might start bleeding off some of the additional energy it attains in other forms such as EM radiation. The reason the metric expansion of space is different is it's not moving THROUGH space, the space itself is stretching.

Just as we discovered dark energy in 1998, the door is open to learn more about about the profile of accelerating expansion over time, which I'm sure we will. More accurate measurements are still being made and we'll have to see what adjustments to our models will best fit the observed data, so I wouldn't completely rule out the possibility of finding something more complex going on.

a reply to: Arbitrageur

I've got one....

If empty space is not indeed empty, and that at the fundamental level of reality chaos gives rise to all matter and energy.... Then wouldn't that mean the laws of thermo dynamics would be a very crude discription of the truth...

If so then that must mean there is plenty of room by which reality my not reflect the laws.....

and if we can get to that far, then surely we can no longer trust the laws of Thermodynamics at all?!?

I pose this question as it appears given entropy the universe is heading for a heat death... an expansion to the point where nothing moves.... Absolute Zero uniform temperature...

But doesn't that in itself violate empirical evidence that clearly shows us that nothing is very perfectly even in nature.... that two values can never be the same regardless of how interconnected they may be.

I discussed this thread of thought with a few colleagues one of which stated that Entanglement is one example of nature perfectly balanced.

This got me thinking if Chaos gives rise to reality then the death of reality would have to rise from pure order???

Food for thought?

Anyone?

originally posted by: Korg Trinity
a reply to: Arbitrageur

I've got one....

If empty space is not indeed empty, and that at the fundamental level of reality chaos gives rise to all matter and energy.... Then wouldn't that mean the laws of thermo dynamics would be a very crude discription of the truth...

If so then that must mean there is plenty of room by which reality my not reflect the laws.....

and if we can get to that far, then surely we can no longer trust the laws of Thermodynamics at all?!?

To paraphrase George Box, all models are wrong, but some are useful. Laws are less reliable than well developed theories and we see laws broken all the time in certain circumstances. The 2nd law of thermodynamics can be and has been broken, however, this doesn't mean we should throw it out. This is just a limitation of laws not being as comprehensive as well developed theories and our well developed theories can explain to our satisfaction WHY the 2nd law of thermodynamics was broken.

We often cite the 2nd law as the reason why "free energy" is a flawed concept, but if you re-define "free energy" as getting enough energy to power a digital wristwatch for one nanosecond, you might actually be able to get that much if you repeat the experiment enough times to "get lucky" and have the statistics go your way.

So none of these experiments proving the 2nd law of thermodynamics can be broken convince me that I shouldn't trust the 2nd law. I do to a large extent, but there can be small exceptions and i'm aware of those which are interesting theoretically but don't have much practical value. What am I really going to accomplish with enough "free energy" to power a digital watch for a nanosecond? Maybe getting credit for publishing the result but nothing of practical value that I can think of.

I pose this question as it appears given entropy the universe is heading for a heat death... an expansion to the point where nothing moves.... Absolute Zero uniform temperature...

But doesn't that in itself violate empirical evidence that clearly shows us that nothing is very perfectly even in nature.... that two values can never be the same regardless of how interconnected they may be.

I don't know if you've been reading this thread lately, but a number of recent questions have asked about things which might have theoretically small differences which for all practical purposes are the same. So it falls into a discussion of accuracy, semantics, and how much is important enough to worry about. The recent examples are tides in ponds, difference of a boat's speed in fresh versus salt water, and now your question on temperature differences. I'll give you one of my favorites. If you knock a paperclip from your desk and it falls to the floor, does the paper clip accelerate toward the Earth, or does the Earth accelerate toward the paper clip? It's a trick question because in theory the answer is both and that wasn't one of the answers offered. But in practice of course the acceleration of the Earth toward the paper clip is too small to measure.

So, when the differences in temperature get too small to measure, sure they might exist but if you can't measure the differences, how important is that?

Here's the description of the final stage of the universe's heat death called "The Dark Era" suggested by one paper:
arxiv.org...

The Dark Era. η > 100. At this late time, protons have decayed and black holes have evaporated. Only
the waste products from these processes remain: mostly photons of colossal wavelength, neutrinos,
electrons, and positrons. The seeming poverty of this distant epoch is perhaps more due to the
difficulties inherent in extrapolating far enough into the future, rather than an actual dearth of physical
processes.

I discussed this thread of thought with a few colleagues one of which stated that Entanglement is one example of nature perfectly balanced.

This got me thinking if Chaos gives rise to reality then the death of reality would have to rise from pure order???

I don't really follow those last two lines so can't comment on those. Pair production of an electron and a positron for example seems like a better example of balance to me with the positive and negative charges canceling each other out.

originally posted by: Arbitrageur
a reply to: Arbitrageur
don't really follow those last two lines so can't comment on those. Pair production of an electron and a positron for example seems like a better example of balance to me with the positive and negative charges canceling each other out.

This would work...

What I mean is that at the Planck scale where reality is formed due to chaos, then in heat death, the chaos must be uniformly ordered.

I wonder if one might describe this as the crystallization of space-time?

a reply to: Arbitrageur

Asking the unknown is impossible,anyhow you asked for it.Any thoughts on the true nature of dark matter?

a reply to: AuroraZ7
You're standing on one type of dark matter (the Earth is made of baryonic dark matter), but measurements suggest there has to be another type which is non-baryonic (which means it's not made of normal stuff we're familiar with like the Earth). I don't know if you're familiar with neutrinos. They could account for some of it and they don't interact much, as billions of them pass through your body and the entire Earth without interacting. One of the most likely candidates is another particle that interacts even less than the neutrino meaning it will be very difficult to detect, but a dark matter physicist on ATS wrote a thread describing how the experiment his team is working on is trying to detect such WIMPs or "Weakly Interacting Massive Particles":

Direct Dark Matter Detection [A review]

There are other possibilities, but discussing those gets pretty involved, so maybe start by reading that thread and feel free to ask any follow up questions.

a reply to: Arbitrageur

Antimatter's a possible one,but surely it would then be visible in a sort as it attacks the matter. Astrophysics is a ass.

originally posted by: AuroraZ7
a reply to: Arbitrageur

Antimatter's a possible one,but surely it would then be visible in a sort as it attacks the matter. Astrophysics is a ass.

Not really, for several reasons.

First, antimatter would look pretty much like matter from cosmological observations. So the fact that the missing dark matter isn't baryonic means that if ordinary matter can't explain observations, ordinary antimatter can't either.

Second, what you said about the "attack" or annihilation in any boundary region where matter meets antimatter would give off radiation and thus wouldn't be dark, and we've been looking for such regions without finding them, therefore we don't think there's a lot of antimatter out there.

a reply to: Arbitrageur

Alas what does anyone actually know anyway.

a reply to: AuroraZ7
One scientist knows a great deal about his particular area of specialty, but can't be an expert in the whole field or other fields as there is simply too much information. But if you add up the sum of human scientific knowledge, Professor Price said it was doubling every 15 years. So one answer to your question is that today we know maybe about twice as much as we knew 15 years ago, four times as much as we knew 30 years ago, and so on.

A Very Short History Of Big Data

Derek Price publishes Science Since Babylon, in which he charts the growth of scientific knowledge by looking at the growth in the number of scientific journals and papers. He concludes that the number of new journals has grown exponentially rather than linearly, doubling every fifteen years and increasing by a factor of ten during every half-century.

That was decades ago and the knowledge doubling rate is probably even faster than every 15 years now, though the rate also varies by scientific field.

a reply to: Arbitrageur

could help me with some thoughts ?

so called antimatter particle was detected in a cloud chamber, right ?

any luck in creation pictures of anti-proton ?
somehow google is not showing any reel pictures of anti-proton trail in a gas chamber...
I would really like to compare them two.

... if opposite charged particles attract and the same time annihilate,
how comes "positron" goes through led and just slows down ?
look how thick it is ?
so... annihilation or no annihilation ?
maybe error in code ?

what about the gas molecules ?

originally posted by: AuroraZ7
a reply to: Arbitrageur

Asking the unknown is impossible,anyhow you asked for it.Any thoughts on the true nature of dark matter?

The one I think is most interesting to think about is a shadow unIverse. Basically dark matter doesn't interact without matter. But it does interact with itself. Picture an entire universe with dark stars and dark planets could even be dark people. And they are wondering why they can't find the missing mass in their universe either. Basically the theory goes were not looking for one particle to explain dark matter instead its just like our matter interacts and forms particles. Even would have their own version of photons. The only thing we do see is the gravitational effects. I read the is last year so I'll have to look back into it to see who's idea it was.