61

Physics, Astronomy & Cosmology / Re: Can we see space expanding?

« on: 13/03/2018 22:46:03 »

.....what would be the current rate of expansion?

I understand t the expansion rate of the Universe is reckoned to be 67.3 kilometres per second per megaparsec.  You probably know that a megaparsec is defined as a distance equal to 3.26 million light years. 

62

Physics, Astronomy & Cosmology / Re: What is the truth about tachyons, baryonic string theory, and quantum mechanics?

« on: 24/02/2018 18:00:03 »

I’m certainly no expert, but here are some thoughts about the tachyon, just to set the ball rolling.

The tachyon is a theoretical particle that always travels faster than light.  It is never accelerated from subluminal to superluminal speed, so it doesn’t contravene the rules of SR, but it does travel backwards through time, relative to us, which raises some interesting thoughts.

You may have seen the quote from John Gribbin at:

https://www.thenakedscientists.com/forum/index.php?topic=72229.0

“So if a tachyon were created in some violent event in space, it would radiate energy away furiously…..and go faster and faster, until it had zero energy ……and was travelling at infinite speed”.

To detect a tachyon, one would have to look for an event, the cause of which had not yet happened.

The prospect of looking for something that may be travelling at infinite speed, may be undetectable and, in any case, has not been formed yet, does seem to be quite a daunting task. 

63

Physics, Astronomy & Cosmology / Re: Did the Big Bang happen where Earth now is?

« on: 14/02/2018 20:11:45 »

 As far as I am aware, s channel scattering is a feature of Mandelstam/Bhabha scattering.   I found the maths involved here totally off-putting, so an idiot-level explanation of how s channel scattering relates to this topic would be much appreciated.

64

Physics, Astronomy & Cosmology / Re: Did the Big Bang happen where Earth now is?

« on: 14/02/2018 19:24:38 »

I suppose it is possible that light from these boundary objects will never reach us, considering that Sol only has 7,600,000,000 years until it swallows the Earth.

They might also fail to reach us if the distance between them and us is increasing at superluminal speed.

65

Physics, Astronomy & Cosmology / Re: Did the Big Bang happen where Earth now is?

« on: 14/02/2018 19:20:05 »

This also echoes what bill said:  And so is everything/everywhere else in the Universe.

There was no intention of invoking quantum entanglement here.

At risk of trying to teach my grandmother to suck eggs, I’ll use the balloon analogy to show how I understand the situation. 

Imagine an uninflated balloon on which you mark a small dot.  As you inflate the balloon, the dot grows.  Now, ask yourself where, within that enlarged patch, you might find your original mark.  Obviously, the answer must be “everywhere”.  The same can be said of the Big Bang.  At the instant of “creation” it encompassed the entire Universe, and as the Universe has expanded it has continued to do that; it has not left behind some original Big Bang site. 

Having said, and perhaps accepted, all this; if we return to the balloon analogy, there must always be a feeling that because the mark expanded evenly in every direction from the centre, that must be its spreading centre.  I suspect that it is this feeling, rather than an inability to accept that the Big Bang happened everywhere, that is the hitch-hiker’s chief difficulty.  Obviously your original dot has expanded, but has it spread across the balloon?  The answer has to be “no”, because the material of the balloon has expanded, carrying your mark with it.  It is tempting to think that your spot was made in the centre of the extended mark, but such is not the reality, either in the case of your dot, or the Universe.

66

Physics, Astronomy & Cosmology / Re: Is there a gradient from the event horizon to the singularity of a black hole?

« on: 13/02/2018 18:26:06 »

You can approximate infinity.......  It just means the object escapes completely and has no likelihood of being recaptured.

Which, sort of, supports what I have said on a number of occasions: "mathematically malleable infinities are approximations".  Thanks, Jeffrey. 

67

Physics, Astronomy & Cosmology / Re: Did the Big Bang happen where Earth now is?

« on: 13/02/2018 18:14:11 »

My conclusion: The Earth is now where the Big Bang happened.

And so is everything/everywhere else in the Universe.

68

Physics, Astronomy & Cosmology / Re: Is there a gradient from the event horizon to the singularity of a black hole?

« on: 13/02/2018 00:41:11 »

That sounds reasonable, but would suggest that "infinity" = an unspecified distance, in this case.

69

Physics, Astronomy & Cosmology / Re: Is there a gradient from the event horizon to the singularity of a black hole?

« on: 13/02/2018 00:10:22 »

  Conversely, an object freely falling from infinity will be moving at the speed of light upon reaching the horizon.

You will not be surprised that I have some reservations in this regard.  An object freely falling from infinity would never arrive.  I assume, therefore, that infinity is being used figuratively. 

Given that that might be the case; what sort of distance would be required for the speed of the falling object to approach, closely, the speed of light?

70

Physics, Astronomy & Cosmology / Re: Can macroscopic objects be considered quantum objects?

« on: 10/02/2018 19:09:56 »

Would it be fair to say that a start has been made in that direction? 

E.g. buckeyballs have 60 carbon atoms, so must be considered as macroscopic objects, but they show quantum characteristics in the double slit experiment.

71

Physics, Astronomy & Cosmology / Re: Is there a gradient from the event horizon to the singularity of a black hole?

« on: 10/02/2018 18:50:58 »

Pop Sci books, and even experts, talk about BH singularities as though they were objects that physically exist.  For us hitch-hikers it is important to remember that this can easily be misleading.

I have quoted Chris Baird on this subject before, but I think the point is worth stressing.   

In the real universe, no black holes contain singularities. In general, singularities are the non-physical mathematical result of a flawed physical theory. When scientists talk about black hole singularities, they are talking about the errors that appear in our current theories and not about objects that actually exist. When scientists and non-scientists talk about singularities as if they really exist, they are simply displaying their ignorance.

    A singularity is a point in space where there is a mass with infinite density. This would lead to a spacetime with an infinite curvature.  Singularities are predicted to exist in black holes by Einstein's theory of general relativity, which is a theory that has done remarkably well at matching experimental results. The problem is that infinities never exist in the real world. Whenever an infinity pops out of a theory, it is simply a sign that your theory is too simple to handle extreme cases.

72

Physics, Astronomy & Cosmology / Re: What would micro black-holes made at the large hadron collider (LHC) look like?

« on: 07/02/2018 21:24:30 »

 

Now, what would that residue be?

I'm afraid you need someone with much more knowledge than I have to answer that.
Matt Strassler https://profmattstrassler.com/ might be a good starting point.

73

Physics, Astronomy & Cosmology / Re: What would micro black-holes made at the large hadron collider (LHC) look like?

« on: 07/02/2018 20:58:57 »

My understanding is that if such a micro black hole were artificially produced, it would spontaneously evaporate, so it would be identifiable only by its "residue". 

I know very little about it, but I believe extra dimensions of space would be required in order to produce micro black holes with our current technology; so it may be a long time before a physical example is produced.

74

Physics, Astronomy & Cosmology / Re: Why is time one-dimensional?

« on: 03/02/2018 21:39:39 »

My argument has been though changing the idea of time "could" bring significance to the golden best tool we have, as yet, discovered with which we can gain understanding of the Universe. If the “golden ratio” helps with our understanding, so well and good, but let’s not try to read anything causative into that.   ratio, especially if an algorithm for time represented the golden ratio.

Ever since philosophers, and later scientists, realised that the best tool they had for describing the Universe, was mathematics there has, in my opinion, been a tendency to interpret this as saying that the Universe was based on mathematics.  This must flirt with the ideas of intelligent design. 

Perhaps it would be better just to think of mathematics as the

75

Physics, Astronomy & Cosmology / Re: Is it possible to build a gravity shield?

« on: 02/02/2018 20:39:22 »

This implies that the field should be considered as independent of the force carrier.

Thinking about this raises some questions in my mind.

Popular explanations of gravity, according to GR, tend to follow this pattern:

1) Visualise empty space (spacetime?).
2) Introduce a mass.
3) The mass causes spacetime to warp.
4) The warping of spacetime = gravity.
The question this seems to leave open is: What is the source of the energy that warps spacetime?

Perhaps there is another way to look at it.

1-2) As above.
3) The mass gives rise to gravitational force (GF).
4) This GF is best described (mathematically) in terms of spacetime curvature.
The wording of the question in the first scenario may change, but the question remains unanswered.
Three other questions must be added.
1) Is spacetime actually curved?
2) What would curved spacetime look like?
3) Is what we describe as curvature simply the imposition of directionality on spacetime?

76

Physics, Astronomy & Cosmology / Re: Did TIME Have To Manifest First ?

« on: 09/01/2018 23:11:35 »

[quote = Jeffrey] It all depends upon point of view. [/quote]

Precisely!  and our point of view is, strictly, the point of view of out 3+1D, linear Universe.  This is the "explicate order". 

What we cannot see, directly, is the "implicate order"; but should that stop us from, at east, trying to apply reason and logic to our consideration of it? 

 

77

Physics, Astronomy & Cosmology / Re: Did TIME Have To Manifest First ?

« on: 08/01/2018 12:13:31 »

whajafink ?

I "fink" this question goes round in circles and probably leads to the "conclusion" that time was not created, it is simply our means of measuring change.  Change then becomes something we perceive, in order to make sense of our "perceived" Universe. 

It's all an illusory "shadow" of an underlying reality.

Come back David Bohm, all is forgiven. 

78

Physics, Astronomy & Cosmology / Re: Are black holes the oldest known part of the Universe?

« on: 22/12/2017 17:21:59 »

In any case, however they started out, they grew by collecting matter.

It seems that stars can do that too.

https://www.laboratoryequipment.com/news/2017/12/winking-star-may-be-devouring-wrecked-planets?et_cid=6217419&et_rid=517749120&type=headline&et_cid=6217419&et_rid=517749120&linkid=https%3a%2f%2fwww.laboratoryequipment.com%2fnews%2f2017%2f12%2fwinking-star-may-be-devouring-wrecked-planets%3fet_cid%3d6217419%26et_rid%3d%%subscriberid%%%26type%3dheadline

79

Physics, Astronomy & Cosmology / Where does the energy come from?

« on: 20/12/2017 22:08:39 »

I found this question asked by a long since vanished poster in another forum.

It was not answered, and as I no longer post in that forum, I am bringing it here.

My initial thought is that if an object is moving it has kinetic energy, so any radiation would decrease its kinetic energy.

Am I on the right track?

80

Physics, Astronomy & Cosmology / Re: If I moved backwards at the speed of light holding a torch, what would happen at the start of th

« on: 22/11/2017 16:17:56 »

In a universe containing only one object with the only two states the object has are constant velocity and straight line motion and that is the only thing observable then how would the passage of time be marked?

In it's own inertial frame of reference nothing is happening.

Indeed, how would space or motion be measured.

I found this in my notes from a few years ago, when I was struggling with some basic ideas. 

I remind others that I write my notes as though I were trying to explain a point to someone with even less knowledge than I might have, so anything that sounds patronising is not intended as such.

“Imagine you are in a space craft at the “centre” of an infinite, void.   Nothingness stretches infinitely in every direction.  You perceive yourself as being stationary, but suppose you engage your engine and travel at fractionally below light speed for five seconds, then stop.  You review your position; are you 1,500,000 kilometres away from where you started?  Is there now more nothingness behind you than there is in front?  On reflection you conclude that there is still an infinity of nothingness in every direction.  There is in fact nothing to which your motion can be relative.  You have “moved”, but you are still in the same place - in the “centre” of an infinity of nothingness - your movement has no real meaning. 

You can argue that if you use your engine to propel your craft forward you will be able to detect your motion, as you will be accelerating, and accelerated motion can be felt by the person doing the accelerating. Undoubtedly this is so, but as you had no way of telling if you were in motion or not before you engaged your engine, you cannot tell if you have moved off from a standstill, if you have simply increased the speed at which you were already travelling, or if you have decreased your speed; which would be the case if you had already been travelling “backwards” without being aware of that fact. 

However, because no matter how far you move, you will still perceive yourself as being in the same place, the whole question of how far you might have travelled, and at what speed, is purely academic.”