Vacuum Bubbles

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Stephen
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Vacuum Bubbles

Post by Stephen » Tue May 03, 2011 5:02 pm

Hi everyone,

I'm sure you remember I used to be afraid of the LHC creating vacuum bubbles in the Pb + Pb collisions back in November. Lately, I've started fearing the LHC going into higher energies in 2014. The reason I'm worried is because no direct measurements of lead cosmic rays at energies higher than 2.76 TeV per nucleon were made.

But as I remember, you guys gave me some reassuring safety arguments in the chat a few months ago. I'm going to repeat them, just to make sure everything was covered.

The first safety argument, is the abundance argument which basically says the abundance of all the elements in cosmic rays is roughly the same as in our solar system, and therefore lead cosmic rays exist, even if we can't measure them yet.

In addition, the RHIC safety report authors invented a formula which can be used to calculate the number of specific heavy ion collisions in the entire history of the planet. The formula still applies to the higher energies of the LHC, and the number calculated is much higher than the number of heavy ion collisions expected in the LHC.

The second safety argument, is the existence of iron cosmic rays in energies higher than 1000 TeV. Because heavy ions behave the same in an electric field, we can conclude lead collisions are safe based on iron cosmic rays.

The third safety argument is the moon argument. Our moon is consistent of heavy ions including lead, and much more powerful collisions have been taking place on the surface of it for the past 5 billion years, and no vacuum bubbles were created. Therefore, we can safely say the LHC would not be creating them as well.

I would appreciate any comments on the issue. Have I missed any safety arguments concerning Pb + Pb collisions? In addition, can anyone please explain to me why iron cosmic rays imply lead collisions are safe? I understand it's because of heavy ions' behavior in an electric field, but I'm not sure I get what it means.

Thanks in advance.

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Re: Vacuum Bubbles

Post by CharmQuark » Thu May 05, 2011 5:25 pm

Just to let you all know that I am actually in the background watching ;)
Anyone who doesn't take truth seriously in small matters cannot be trusted with large ones either by Albert Einstein.

Stephen
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Re: Vacuum Bubbles

Post by Stephen » Thu May 05, 2011 5:27 pm

Stephen wrote: Can anyone please explain to me why iron cosmic rays imply lead collisions are safe? I understand it's because of heavy ions' behavior in an electric field, but I'm not sure I get what it means.
Can anyone please address my question? oxodoes told me this in chat a few months ago, but I don't understand the logic behind the argument.

Also, does anyone have any safety arguments regarding the formation of vacuum bubbles in lead collisions, in addition to the ones I already mentioned?

The reason I'm not counting the existence of cosmic rays at energies above 10^20 eV as safety arguments, is because they are consistent of protons, and the RHIC safety report clearly states we have to look at both types of collisions (protons and heavy ions) separately in order to exclude the possibility of a vacuum metastability event.

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Re: Vacuum Bubbles

Post by Kasuha » Thu May 05, 2011 5:45 pm

Stephen wrote:
Stephen wrote: Can anyone please explain to me why iron cosmic rays imply lead collisions are safe? I understand it's because of heavy ions' behavior in an electric field, but I'm not sure I get what it means.
Can anyone please address my question? oxodoes told me this in chat a few months ago, but I don't understand the logic behind the argument.

Also, does anyone have any safety arguments regarding the formation of vacuum bubbles in lead collisions, in addition to the ones I already mentioned?

The reason I'm not counting the existence of cosmic rays at energies above 10^20 eV as safety arguments, is because they are consistent of protons, and the RHIC safety report clearly states we have to look at both types of collisions (protons and heavy ions) separately in order to exclude the possibility of a vacuum metastability event.
It's all addressed in LSAG report:
The conclusion reached in [8] required two well-motivated assumptions.
Since high-energy cosmic rays include many iron nuclei, which are also
prevalent in the Moon’s surface, it was assumed that the conditions reached
in iron-iron collisions are comparable to those reached in the collisions of gold
ions or lead ions that had been studied previously in the laboratory.
Secondly, since RHIC and LHC experiments take place in the centre-of-mass
reference frame, whereas in cosmic-ray collisions the centre-of-mass frame is
moving at high speed, it was necessary to make some assumption about the
velocity distribution of any strangelets produced. We recall that high-velocity
strangelets might well be broken up by lunar matter before becoming slow
enough to coalesce with it.
Since the appearance of [8], the RHIC heavy-ion programme has also studied
the collisions of the copper ions, which are closely comparable to iron-iron
collisions. The abundances of particles produced in these collisions are
described by the same thermal model of a particle furnace that accounts
successfully for particle production in gold-gold collisions. Moreover, the
velocity distributions of all particle species observed at RHIC are similar to or
broader than the distribution assumed in [8]. These observations support the
assumptions made in [8], and therefore strengthen their conclusions.
...
...
[8] W. Busza et al., Rev. Mod. Phys. 72, 1125 (2000).

Stephen
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Re: Vacuum Bubbles

Post by Stephen » Thu May 05, 2011 5:51 pm

I read the LSAG report more than once, and it doesn't state the reason for comparing iron with lead. Maybe I'm missing something?

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Re: Vacuum Bubbles

Post by Kasuha » Thu May 05, 2011 9:26 pm

Stephen wrote:I read the LSAG report more than once, and it doesn't state the reason for comparing iron with lead. Maybe I'm missing something?
You're missing the document marked as [8]. LSAG report is just a summary.

Edit: I believe it is this document. Looks human readable but I'm too tired now to dig in. Happy reading...

Stephen
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Re: Vacuum Bubbles

Post by Stephen » Fri May 06, 2011 6:05 pm

I read the RHIC safety report several times, to be honest with you. In fact, that is the cause for me worrying over the vacuum instability event, since they clearly state we have to look at both types of collisions separately in order to exclude the possibility of it happening. But it doesn't state anything regarding the reason iron cosmic rays can be used to determine lead collisions in the LHC are safe.

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Re: Vacuum Bubbles

Post by Kasuha » Fri May 06, 2011 9:24 pm

Elementary theoretical considerations
suggest that the most dangerous type of collision is that at considerably lower energy
than RHIC. They also suggest that heavy nuclei like iron are reasonable stand-ins for ultraheavy
nuclei like gold.

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Re: Vacuum Bubbles

Post by Stephen » Fri May 06, 2011 9:58 pm

But what are those "elementary theoretical considerations"?

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Re: Vacuum Bubbles

Post by Kasuha » Fri May 06, 2011 10:34 pm

I'd put it this way ... if you are going to believe one physicist saying that vacuum may be metastable, you should also believe another physicist saying that iron is good enough.

Personally I believe Mr. Busza is a well studied man who wants to see scientific results rather than die in a horrific accident so if these considerations are elementary to him I don't have problems accepting that.

If I use a comparison that I see fitting ... it's like if you study colliding snowflakes and snowballs. You sure need to study both because they behave differently. But testing with 5 cm diameter snowballs is clearly going to give you the same discoveries (except for scale) which you can get from studying 6 cm diameter snowballs - especially if you're able to collide the 5 cm ones at much higher energies.

Stephen
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Re: Vacuum Bubbles

Post by Stephen » Fri May 06, 2011 11:13 pm

I understand what you're saying, but that wasn't my question. I simply want to know the reasons for physicists saying iron is comparable to lead.

Kasuha
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Re: Vacuum Bubbles

Post by Kasuha » Fri May 06, 2011 11:20 pm

If you want to go deeper I'm afraid you'll need to start studying quantum physics and make the assumption elementary for yourself.

Personally I'd rather understand the reason why some people are saying vacuum is metastable.

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Re: Vacuum Bubbles

Post by Stephen » Fri May 06, 2011 11:23 pm

I'm going to email some professors asking them my questions regarding this issue. Thanks anyway.

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Re: Vacuum Bubbles

Post by photino » Fri May 06, 2011 11:40 pm

I simply want to know the reasons for physicists saying iron is comparable to lead.
Leaving aside the "theoretical considerations", Kasuha already quoted the relevant pasage:
Since the appearance of [8], the RHIC heavy-ion programme has also studied
the collisions of the copper ions, which are closely comparable to iron-iron
collisions. The abundances of particles produced in these collisions are
described by the same thermal model of a particle furnace that accounts
successfully for particle production in gold-gold collisions. Moreover, the
velocity distributions of all particle species observed at RHIC are similar to or
broader than the distribution assumed in [8]. These observations support the
assumptions made in [8], and therefore strengthen their conclusions.
(It might help to look at where iron and copper (and lead and gold) are on the periodic table, and to compare the composition of the nuclei.)

I.e. there is a lot of experimental data from RHIC on copper-copper and gold-gold collisions (and by now probably also from the LHC lead-lead collisions), so the comparability has been tested and verified.
Last edited by photino on Fri May 06, 2011 11:48 pm, edited 1 time in total.

Stephen
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Re: Vacuum Bubbles

Post by Stephen » Fri May 06, 2011 11:44 pm

Thanks for clarifying that one, photino. But what about the behavior of heavy ions in an electric field? Doesn't it have anything to do with it?

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