Speed of Light and Energy...?

[mistermack]

Hi colubridae, I don't know what I want, if anything, from this site. I just enjoy juggling ideas, and reading other peoples' opinions. I assume that if someone bothers to reply, they do it freely because they thought about my post.

As far as religion goes, I'm about as atheist as they come, except that you have to allow that almost anything is 'possible', so don't think I'm going to suddenly declare that jesus is truth. I didn't think I'd given that impression, but if I did, sorry.

As for the point of the big bang, I haven't heard or read anything definitive on why there should be no space there, or where space stops and nothing begins.
Anyway, a frame of reference doesn't rely on there being space or matter.

Re wikipedia, like most people I don't rely on it, but it's the best compromise out there, and much smarter people than me use it all the time. All I can say is that I usually leave it knowing more than when I opened it. I appreciate that.

[newolder]

So why can't we calculate where we are relative to the point of the big bang, and work out our motion relative to that?

The “point of the big bang” (should such a thing exist) is hidden from direct electromagnetic view by the surface of last scattering when the observable universe cooled sufficiently for neutral atoms to form from the pre-existent plasma state. This surface is mapped by the WMAP & Planck telescopes and looks like a very smooth sphere. Our frame of reference is not co-moving with the WMAP sphere. If it were, there would be no dipole on the sky: see, for example, Ned Wright's History of the CMB Dipole Anisotropy

[mistermack]

Hi Twiglet, I imagine a system that contains just a small ball bearing, and a large star, heading for each other at closing speed of 1000 kph. From the frame of a stationary ball bearing, the system has immense kinetic energy. From a stationary star frame of reference, the system has tiny kinetic energy.
If the total energy of the system is the mc2 part, plus the kinetic energy, then I assume the mc2 part must be less in the example where the star is moving at 1000 kph.
I can picture that, if time is slower for the moving star. So my answer, I suppose, is that kinetic energy IS relative. Energy is conserved, and you just experience it differently, depending on the motion of your frame of reference.

[Twiglet]

Hi Twiglet, I imagine a system that contains just a small ball bearing, and a large star, heading for each other at closing speed of 1000 kph. From the frame of a stationary ball bearing, the system has immense kinetic energy. From a stationary star frame of reference, the system has tiny kinetic energy.
If the total energy of the system is the mc2 part, plus the kinetic energy, then I assume the mc2 part must be less in the example where the star is moving at 1000 kph.
I can picture that, if time is slower for the moving star. So my answer, I suppose, is that kinetic energy IS relative. Energy is conserved, and you just experience it differently, depending on the motion of your frame of reference.

It's relative in the sense that, as an observer, you could argue how much KE each object has, but you would completely agree about how much energy has been "added" by throwing the ball. or shooting the ball bearing.

Language is critical here. Energy is conserved within the system. For KE there is no dispute about that, only where the energy resides. The core principle is conservation within the system.

[hackenslash]

Hackenslash wrote that the speed of light is the only frame of reference that everything moves relative to.
Is that strictly true? I wouldn't call it a frame of reference. It's an unvarying property of electromagnetic waves.

It's both. It is an unvarying property of electromagnetic waves and the way they propagate. The key distinction here is that it never changes, regardless of how fast you're moving. As such, it is always the same and, being the only thing that is absolutely constant regardless of your frame of reference, it is the one fixed point in the universe by which we can measure anything. As such, it is the only frame of reference that everything moves relative to.

When I looked up mass in wikipedia, they referred to the invariant mass of a system being calculated from the 'centre of momentum' frame of reference.
If you apply that to the entire universe, that frame of reference goes through the point of origin of the big bang. That point must still be the centre of momentum of the Universe, so that frame of reference must still be valid, and we all move relative to it. ( You can't move the centre of gravity of the Universe, without creating immense quantities of energy ).

This is more complicated to explain, especially without an understanding of the topology of the dimensional manifold. In short, though, there can be no centre of gravity to the universe, because there is no centre. The entire notion of centre is a reference to a spatial location.

So why can't we calculate where we are relative to the point of the big bang, and work out our motion relative to that? After all, it's the one 'real' frame of reference, whereas all others are arbitrary.

Because there was no point of the big bang. This again makes reference to a spatial location, which is invalid in this context, because there was no space before the big bang. The big bang represents the expansion of space-time or, if M-Theory and other multi-dimensional constructs have any basis in reality, the unfolding of our familiar spatial dimensions from the dimensional manifold. If you think about what the properties of those hidden extra dimensions actually are in those theories, it highlights the problem nicely. If the other dimensions are curled up really small so that we can't see them, it leads to the question 'where are they, then?' to which the answer is 'everywhere'. In other words, ALL dimensions exist simultaneously at ALL points in the other dimensions. This is extremely counter-intuitive, of course, which is why so much work goes on in M-Theory in trying to understand the topology of the dimensional manifold. It isn't just a problem for visualising the nature of the cosmos, and particularly the idea that the cosmos has no centre, it also has implications for how gravity propagates. Some of this is addressed in Turok's work, in which he suggests that the reason for gravity being so weak on our world-brane is that it is propagating through other dimensions, weakening its effects.

These are mostly failures of language and concept. In other words, we don't have the words to properly describe them. How do you explain the colour blue to somebody who has been blind from birth? In the same way, we lack the linguistic tools to describe things that are so far removed from, or counter-intuitive to, our middle-world experience. Sagan's 'Flatland' is possibly the best example of how our thinking fails when we try to imagine things that are outside of our experience.

As for the point of the big bang, I haven't heard or read anything definitive on why there should be no space there, or where space stops and nothing begins.
Anyway, a frame of reference doesn't rely on there being space or matter.

Well then you haven't read anything on the topic. The big bang represents the unfolding of space. Before the big bang, there was no space, unless of course you get down to the Planck scale, which is as small as we can reasonably apply.

Oh, and a frame of reference most certainly does rely on there being space. There are features of relativity that only apply inside our cosmic expansion, as far as we can tell. Apart from anything else, the expansion of the cosmos is not subject to light-speed limitations.

[hackenslash]

I knew there was something I meant to add. There is another possibility with regard to the 'centre of the universe' idea, and it can again employ the age-old balloon analogy. It is possible that there is a centre of the universe, but that it exists in a dimension that we are not aware of. Much like the ant on the surface of an expanding balloon, there is a centre of the balloon, but the ant is unaware of it, because it exists in a dimension that the ant can't see.

This is mere speculation, of course, and no real weight should be given to it at this point, but it at least provides a slightly more intuitive way of looking at it, and especially at the limitations of our understanding of dimensional topology.

[Twiglet]

So hackenslash, without resorting to string theory, aren't we just left staring into the rift of questions that ever-bigger particle accelerators hope to answer, without ever really resolving the fundamental issue of how quantum uncertainty works in an extremely energy-dense near-c universe?

As far as I understand it, String theory is some pretty maths trying to attach itself to experimental results, without too much in the way of prediction.

[hackenslash]

So hackenslash, without resorting to string theory, aren't we just left staring into the rift of questions that ever-bigger particle accelerators hope to answer, without ever really resolving the fundamental issue of how quantum uncertainty works in an extremely energy-dense near-c universe?

I don't think so, no. The whole point of ever-bigger particle accelerators is precisely to get to the bottom of what's actually going at those energy densities and velocities (and scales; the larger the accelerator, the greater the energies, and the greater the energies, the smaller and smaller scales we can probe)*. Only by getting to those densities can we actually hope to understand the role of uncertainty when dealing with relativistic velocities and masses.

As far as I understand it, String theory is some pretty maths trying to attach itself to experimental results, without too much in the way of prediction.

Well, that's certainly what the detractors say, but it isn't entirely justified. Firstly, String Theory is an extension of the known laws of physics. It isn't just pulled out of the air, as some would suggest. The mathematics involved invokes well-established physical principles in their mathematical forms and begins to extrapolate from there, so it isn't wholly without basis in reality. Moreover, some predictions have arisen out of it, in the form of the predictions concerning gravitational waves and their expected energies that arise from the work of Turok and Steinhardt.


* It should be noted that the problem some have with string theory is that, if the scale of the postulated strings or branes is anywhere near the Planck scale, they are not realistically testable, even where testable in principle, because the energies required to probe such small scales would require and accelerator about the size of the solar system

[Twiglet]

So hackenslash, without resorting to string theory, aren't we just left staring into the rift of questions that ever-bigger particle accelerators hope to answer, without ever really resolving the fundamental issue of how quantum uncertainty works in an extremely energy-dense near-c universe?

I don't think so, no. The whole point of ever-bigger particle accelerators is precisely to get to the bottom of what's actually going at those energy densities and velocities (and scales; the larger the accelerator, the greater the energies, and the greater the energies, the smaller and smaller scales we can probe)*. Only by getting to those densities can we actually hope to understand the role of uncertainty when dealing with relativistic velocities and masses.

As far as I understand it, String theory is some pretty maths trying to attach itself to experimental results, without too much in the way of prediction.

Well, that's certainly what the detractors say, but it isn't entirely justified. Firstly, String Theory is an extension of the known laws of physics. It isn't just pulled out of the air, as some would suggest. The mathematics involved invokes well-established physical principles in their mathematical forms and begins to extrapolate from there, so it isn't wholly without basis in reality. Moreover, some predictions have arisen out of it, in the form of the predictions concerning gravitational waves and their expected energies that arise from the work of Turok and Steinhardt.


* It should be noted that the problem some have with string theory is that, if the scale of the postulated strings or branes is anywhere near the Planck scale, they are not realistically testable, even where testable in principle, because the energies required to probe such small scales would require and accelerator about the size of the solar system

Re string theory, I'm speaking from a position of comparative ignorance. I graduated physics from Manchester uk in 1991. Many of my friends considered going into string theory, but even then, it was considered as something of a dead end. I went into industry. Most of my friends who stayed with physics went on to solid state and material science. The more theoretically inclined went on to stuff like robotics.

In the ensuing years string theory looked like something of a dead end. Has it enjoyed some kind of renaissance?

I understand the appeal of it - it doesn't destroy anything and it might reconcile a few things, but beyond that, it doesn't seem much more predictively useful than the flying spaghetti monster. If you can tell me otherwise, I'll be happy to hear it, but by tell me, I mean specific predictions coupled with experiments devised to test them. Are there any?

[mistermack]

I realised as I wrote it that I'd get kicked for saying that about a frame not needing space, but I let it stay to see what was wrong with it.

As for other dimensions, I'm entirely happy with them being all around us.
The dimensions we experience are properties of the energy and matter we see and feel. If we can't see or feel or detect something, we won't be aware of it's properties.
If you imagine a universe made of solid copper, and energy and matter was just composed of eddying electricity, it's feasible that there could be beings who only experience other electrical currents, and had no way of detecting the solid copper matrix. They would move through it as if it wasn't there.
That's just a mind picture I've used for years, there could be thousands of others.

[hackenslash]

Re string theory, I'm speaking from a position of comparative ignorance.

Well, I'm hardly an expert, except in the sense that an 'ex' is a has-been and a 'spurt' is a drip under pressure.

I graduated physics from Manchester uk in 1991. Many of my friends considered going into string theory, but even then, it was considered as something of a dead end. I went into industry. Most of my friends who stayed with physics went on to solid state and material science. The more theoretically inclined went on to stuff like robotics.

A good university. I live about 2 miles away.

In the ensuing years string theory looked like something of a dead end. Has it enjoyed some kind of renaissance?

Yes, in the form of the formulation of M-Theory. This could get long, but I'll try to keep it as brief as possible. Basically, there were 5 branches of string theory. In each theory, there were problems associated with doing calculations when a certain value, the coupling constant, approached 1, in that they gave solutions of infinity. These all gave different results when employing perturbative approaches. However, in 1994, it was discovered that there are relationships between the theories, known as dualities.

The first is known as 'S' duality. This happens when one theory at strong coupling values is equivalent to another theory at weak coupling values. The second is 'T' duality. This happens when one theory, compactified on a large volume of space, is equivalent to another theory compactified on a small volume of space. The third is 'U' duality, which is essentially a combination of the other two dualities.

The thing that actually triggered the revolution, known as the second superstring revolution, was the discovery of 'T' duality, because it allowed for calculations using a non-perturbative approach. It was actually realised that all these theories were in actual fact one single theory, due to this 'web of dualities'. It has been likened to a group of blind men attempting to describe an elephant by touch alone. One grabs the trunk and thinks it's like a snake, another grabs the tusk and describes it as hard and smooth, etc. Further, these dualities allowed for a wide range of quantum-mechanical solutions, which led to the unification of all the string theories, along with 11-dimensional supergravity, into one over-arching framework, known as M-Theory.

I understand the appeal of it - it doesn't destroy anything and it might reconcile a few things, but beyond that, it doesn't seem much more predictively useful than the flying spaghetti monster. If you can tell me otherwise, I'll be happy to hear it, but by tell me, I mean specific predictions coupled with experiments devised to test them. Are there any?

Well, going back to Turok's predictions concerning how gravity propagates through the dimensional manifold, this can be detected at the LHC with it's gravitational wave detectors. If the values match Turok's predictions, he wins a Nobel prize and, while this would not actually demonstrate that string theory is true, it would be seen as confirmation that it's on the right track. More importantly, it provides a means for falsification.

[Twiglet]

Thanks hackenslash. Please don't feel obliged. Just point me in the direction of the new stuff, if you can be arsed. Don't baby me with the explanations, I don't need that stuff, but if I need to get my shit together and catch up, and you can save me a few minutes go ahead

[newolder]

Thanks hackenslash. Please don't feel obliged. Just point me in the direction of the new stuff, if you can be arsed. Don't baby me with the explanations, I don't need that stuff, but if I need to get my shit together and catch up, and you can save me a few minutes go ahead

The arxivs are a fine resource. From Neil Turok's recent output you might find The Return of the Phoenix Universe interesting:

 Honorable Mention at the 2009 Gravity Research Foundation essay competition

[Farsight]

Thanks for the link but I'm in no position to buy any more books. How do you square this 1% with your earlier posts to me (at rd.net, iirc) where you were adamant that the Higgs mechanism plays no part and the lhc will not find anything related?

If 99% of mass isn't down to the Higgs mechanism, that means I'm 99% right. It certainly plays no part in pair production where a massless photon is converted into an electron and a positron. It similarly plays no part in electron-positron annihilation into gamma photons. Since you can also annihilate a proton and an antiproton to get two neutral pions which decay in a nanosecond into gamma photons, I'd say it plays no part in that either. Then I won't be 99% right. I'll be 100% right. It's simple newolder, there's a symmetry between momentum and inertia. A massless photon in a mirror box adds mass to the system, because it isn't going anywhere. In pair production, a self-trapped photon adds mass to the system that is thereby created. Only we don't call it a photon any more, we call it an electron. Or a positron. And to create them, the photon was boson enough.

[Farsight]

When it comes to momentum, my problem has always been with some aspects of relativity. If energy is real, and eternal, can't be created or destroyed, I can't get my head round how it can be relative. i e , two objects moving towards each other. Does one possess the momentum, or the other, or do they both possess part of it?

No, the motion possesses it! Relativity is all about motion. In a deep sort of way, that's what energy is. And matter is made of it.

If energy is a real uncreateable indestructable entity, then to me they must each have an actual momentum, not relative momentum that you can flip from one to the other just by choosing different imaginary axes. And that means that the Universe has to have a fixed frame of reference, that everything moves relative to.

Motion is relative. If you were up in space and a cannonball shot past you at 1000mph you'd say it had a lot of kinetic energy and a lot of momentum. But if you fired your rockets and caught up with it, then as far as you're concerned it hasn't "got" these things any more, because it no longer has any motion relative to you. Having said that, yes, I agree that the universe has a frame of reference, in the CMBR. It isn't quite "fixed" because the universe is expanding. However you can gauge your motion through the universe by reference to it. And the buck stops at the universe.