Hadran massechet Eruvin - Introducing The Laser Eruv!

This Friday Daf Yomi will be finishing Massechet Eruvin - according to many, one of the hardest sections of the Babylonian Talmud.  I am proud to say that this is the second time that I have finished Eruvin with Daf Yomi.  The last time was on the 19th of Av in 1998.  

Learning Eruvin this time around was a completely different experience.  Last time I was a Yeshiva student and everything was theoretical.  This time I am a community Rabbi who had the rare privilege of being able to oversee the establishment of an eruv in my community.  (For the epic saga click here.)

As part of my siyum on Massechet Eruvin, I want to introduce a new practical concept that I hope will make a real impact on the contemporary conversation of the laws of Eruvin.

The contemporary eruv is usually made up of a series of telephone wires that form a contiguous perimeter around a community.  The challenge of establishing a community eruv is finding a route that works, and convincing the utilities company to allow the Jewish community to string extra wire spans where there are gaps.  

If the city has telephone poles that meet the requirements - great.  If not, the construction of an eruv is costly and requires long conversations with the electric company, the traffic engineers, a contractor, a licenced electrician, non-Jewish neighbors (unfortunately sometimes Jewish neighbors), and eventually the chief of police or even the mayor.  Ask any community that has built an eruv - or that is trying to build an eruv - they will all tell you that it is not an easy endeavor.  

Welcome to the future:

Introducing - The Laser Eruv!

The concept is simple.  Four poles are erected at the four corners of the perimeter.  Each of the poles has a small system of mirrors set up.  A laser is perched on the top of pole #1.

The laser from pole #1 shoots towards pole #2.  The beam is caught by the mirror on pole #2 and redirected towards pole #3, caught by the mirror on #3 and redirected towards pole #4, where it is redirected towards pole #1 completing the circuit.

No more time-consuming eruv checks.  A few minutes before Shabbat the Rabbi takes out his smart phone, hits his laser eruv app which operates the laser and sets up the eruv.  The mirrors can even have censors that inform the Rabbi whether the beam hit its target or if the mirrors need adjusting.  

The concept is simple enough to understand and there are countless applications that can be added that can make constructing and maintaining an eruv easier, more convenient, and cheaper than ever before.

The question of course is, does the laser eruv meet the requirements of a kosher eruv?

That is the topic that I wish to address.  

Massechet eruvin opens up with the case of a mavoi (מבוי), a type of alleyway that was common in ancient residential neighborhoods.  The sages forbade carrying in a mavoi unless the community sets up either a koreh (קורה)- a cross beam - placed across the entrance of the alleyway - or a lechi (לחי)- a post planted at one side of the entrance of the alleyway.  

Rashi, on the first mishnah of eruvin (2a), explains that the purpose of the beam or the post is because the mavoi may be confused with a public domain and therefore this reminder is needed to clearly identify the alleyway as such so that people should not think that it is permissible to carry in the public domain.  (other say they act as a virtual wall)

Towards the end of the massechet, on page 80b, the gemara has an interesting discussion regarding the acceptability of certain materials for a koreh or a lechi, particularly an asheirah tree - a tree used for a type of idol worship.

Rav Hiyya Bar Ashi ruled: "A lechi may be made from an Aheirah tree.  Rav Shimon Ben Lakish ruled: "A koreh may be made from an Aheirah tree."  The one that permits a koreh all the more so would permit a lechi.  But the one who permits a lechi would [only permit a lechi and] not a koreh because its measurements are considered as if they are crushed (כתותי מכתת שיעוריה)

That means as follows.

A lechi must be a visible marker.  It has a minimum height of 40 inches but there is no minimum for the width or depth.  This is the accepted halachah.  The lechis that we put on telephone poles for our contemporary eruvs (while they are not the same thing as the lechis we are talking about in this case) must be at least 40 inches high but have no requirements for width or depth.  Some contemporary eruvs use strips of reflector tape for lechis even though the tape is practically one dimensional.

A Koreh on the other hand has stricter requirements.  These requirements are discussed in the third mishnah (13b).

The koreh (beam) that they were talking about must be wide enough to hold a [type of brick] of three hand breadths.  It is sufficient if the beam is one hand breadth wide in order to hold the brick.  Rabbi Yehudah ruled that it is sufficient if the beam is wide enough even if it is not strong enough.  If it was made of straw or reeds it is viewed as if it were made of metal.  

According to both opinions the beam used for a koreh must look a minimum width.  The argument is whether the beam must actually be as strong as it looks.  It is questionable if Rabbi Yehuda would extend his ruling of a straw beam to include a laser beam.  Even according to his lenient opinion the beam may still have to have some substance to it, which a laser beam is lacking.

But in the gemara on page 80b Resh Lakish is talking about an asheirah tree.  An Asheirah tree is a special tree that was designated for a particular type of idolatry.  The law is that an Asheirah must be burned.  Rashi explains that since the Asheirah stands to be burned it is as if its measurements are not real measurements.  (Rashi to Eruvin 80b and Sukkah 31b)

In the words of the Soncino edition footnote, "A thing that is condemned to be burned is regarded as burnt, and since it must be burnt it is regarded as non-existent."

The Asheirah tree is there but not there.  You may be looking at what you think is a tree, but in reality it has no measurements.  A lulav must be at least 4 hand breadths.  Your Asheirah branch looks like it is 5 hand breadths - seemingly a perfectly kosher lulav.  But really it is zero hand breadths because it is not really there.    So an asheirah is not kosher for a lulav.

An Asheirah tree is like a hologram.  It appears to be there, but it is really not there. It is not kosher in cases where there are minimum measurements required, but even according to the opinion of Hiyyah Bar Ashi on page 80b, in cases where there are no minimum requirements an asheirah is acceptable.

This is the fascinating halachic concept of the Asheirah: the branch or wood beam whose measurements have been "crushed" to non-existent particles.  It seems clear that the concept of the Asheirah beam could be applied to the laser beam, a "beam" that is there but not really there.  If an Asheirah tree can be used for an eruv, it seems clear that a laser beam would be acceptable as well.

(an interesting further "proof" of the connection between an asheirah and a laser emerged on the second to last page of eruvin (104a).  It is slightly out of scope so I made it into a different post.  Click here.)

But still, it is only the opinion of Resh Lakish that allows us to use an Asheirah for a koreh.  The halachah follows the opinion of Rav Hiyyah Bar Ashi who does not permit its use.

But the telephone wires that make up our contemporary eruvs are not korehs.  If they were, telephone wires would not be acceptable as they do not meet the width requirements of holding a brick from the mishnah on 13b mentioned above..

The contemporary eruv is actually made up of a series of doorways - known in halachah as a tzurat hapetach (צורת הפתח) - a shape of a doorway.

Each telephone pole represents a side post and the wire is the lintel.

So the question is not whether or not an Asheirah can be used for a koreh.  The question is whether an Asheirah can be used as the lintel of a tzurat hapetach.

On page 11b the Gemara discusses the definition of a tzurat hapetach.

This is perhaps the most important page in the entire messechet with regard to the laws of the contemporary eruv.  The sages argue as to the definition, and the final halachah is found in the shulchan aruch orach chaim 362:11.

What is a tzurat hapetach?  A reed on either side and a reed on top of them.  Even if the reed on top does not touch the supporting reed and there are several feet separating them.  As long as the two side reeds are at least ten hand breadths (40 inches) high and they are exactly underneath the top reed.  If they are attached from the side it is invalid.  And the side reeds must be strong enough to hold a door.

The halachah is clear.  There is no minimum measurement for the reed on top.  The mishnah brurah (362:18) says that it may even be strings.  The Aruch hashulchan (362:31) says the source for this is from the Talmud Yerushalmi that says the lintel can be a piece of reed-grass (גמי).

My contention is it that since there are no minimum requirements for its thickness it can even be an asheirah tree - or a laser beam!

This may sound like a joke, and I must admit that when I first conceived of the idea it kind of was.  But after putting much thought into it I think that I may have stumbled onto something real.

Now I will be the first to admit that I am no expert in the laws of eruv and I in no way consider myself a posek.  This is just an idea that I had.  My hope is that this idea catches the attention of some of the recognized authorities of Jewish law and they take the idea seriously enough to consider if there is any validity to it.

Most halachic authorities live either in Israel or in large cities where eruv is taken for granted.  For them and their communities this is just an interesting theory.  But for Jews in smaller communities this could be a game changer.

But I think that it is worth looking at for the big cities as well.  It may not be today or tomorrow, but is it completely inconceivable to imagine that some time in the future our communications will no longer require telephone wires?  When that happens what will the Jews in the larger communities do when their respective municipalities tell them that the poles are coming down and the eruv with them?  At that point the halachic authorities will be scrambling to figure out how communities can have eruvs.

Let's be prepared.  Forward this to your local Rabbi and see what he says.  Perhaps I am missing a vital piece of information that destroys my whole theory.  Then this will just have been an interesting exercise in Torah for its own sake.

But what if I am right?  What will that mean for the future of eruvs?

Mazal tov to all those finishing massechet eruvin.  Onward to massechet Pesachim where we will learn the laws of Pesach.  For a siyum on pesachim, let;s see if someone can figure out how to get us out of kitniyot, or better yet second day yom tov!

Further reading for laser eruv

As I mentioned in my other post, there is another "proof" for considering an Asheirah tree to be a precedent for a laser beam.

The Gemara says that an asheirah has no real dimensions.  The way that it describes it is

כתותי מכתת שיעוריה

The artscroll translation is:

because the required width measurement of the koreh is nullified, as if the koreh were pulverized, since an asheirah must be burned.  However, a lechi has no minimum width requirement, and thus retains its status even though it must be burned.

Footnote 7 in the artscroll edition says:

Although a lechi must measure ten tefachim in height and a minimal amount in width, since these measurements are nonetheless insignificant the Sages did not rule stringently in the case of a lechi (Tosafos ד''ה אבל).  Maggid Mishnah (Hilchos Shabbos 17:12) explains that only those objects whose three dimensions all have required measurements lose their status when made from the wood of an asheirah (cf. the explanation of R' Avraham in Tos).

I believe that this offers a pretty strong support for the laser eruv as it is agreed that the lintel of a tzurat hapetach does not have a minimum requirement.

In messechet Sukkah on 31b artscroll translates:

so that its measurement is considered pulverized.

The footnote reads:

A Lulav must measure at least four tefachimin order to be valid.  Since the lulav that comes from the asheirah that existed in the time of Moshe must be burned, its measurement is considered as pulverized [as though it has already been burned].  Thus, it lacks the measure required for it to be valid (Rashi).

The footnote goes on to explain the pulverized measurement:

When the halachah condemns an object to be burned, it is viewed in the eyes of the halachah as if it is already reduced to ashes.  In Rashi's words (sukkah 29b, chulin 89b) כל העומד לשרף כשרוף דמי, anything destined to be burned is considered like it has been burned.  This is not to be understood as meaning that the item is considered non-existent, but rather that its destiny renders it insignificant.  Accordingly, any object that requires a minimum size in order to be valid is considered to be lacking that size if the halachah dictates that it be burned.

Many commentators state that the disqualification pertains only to objects that are required to be one organic unit (e.g. a lulav or a shofar).  If a mitzvah acn be performed with an aggregate of small particles, as in the case of s'chach, even material from an asheirah tree would be valid, as if an infinte number of leaves combined to cover the succah.  Their reasoning is that the effect of the rule of the pulverized measurement is that the object is considered disintegrated, a condition that affects only something that must be a unit, such as a lulav or a shofar.  It is not applicable to s'chach, which may consist of many small particles as long as it provides shade (Meiri to Eruvin 14b; Beur HaGra Even HaEzer 124:2; see also Tosafos to Eruvin 80b; Rambam Hil. Shabbos 17:12 with Maggid Misheh and Chidushei R' Chaim HaLevi; Bikurei Yaakov 630:2).

Once again, the lintel of a tzurat hapetach is not similar to a lulav or a shofar.  It can be made up of an infinite collection of particles, in our case light particles.

But I want to focus on the term כתותי מכתת which is translated a "pulverized" or "crushed" by Soncino.

In eruvin on daf 104a, in a completely unrelated discussion the Mishnah says as follows:

בוזקין מלח על גבי כבש בשביל שלא יחליקו

It is permissible to break up salt and scatter it on the ramp of the Altar [on shabbat] so that [the kohanim] do not slip [on it when it is wet].

Rashi discusses the meaning of the word  בוזקין - to break up.  He says that it is synonymous with the word כיתות - to crush as in the term כתותי מכתת שיעוריה.  His source is from two places.  

First he sites a gemara in massechet Yoma 22b.  The gemara is looking to translate a word with the root בזק from the book of Shmuel.  

Rashi's second source is from massechet Haggigah 13b.  The gemara there is trying to understand the cryptic passage from the first chapter of the book of Yechezkel where the prophet tries to describe the vision of the divine chariot.

The verse in Yechezkel (1:14) says:

וְהַחַיּ֖וֹת רָצ֣וֹא וָשׁ֑וֹב כְּמַרְאֵ֖ה הַבָּזָֽק

As is their way, artscroll translates the verse as follows:

And the chayos ran to and fro like the appearance of Bazak.

When they encounter Hebrew words that require more elaborate explanations they just transliterate and give multiple explanations in the commentary notes.

Bazak is a brilliant flash of light.  Rashi gives four interpretation: a) like the colorful light emanating from the fire of a crucible where gold is refined; b) like the quick flame from the highly flammable leftovers of olives in a pot; c) something quickly spreading out; d) like lightning.

Metzudas Zion explains that bazak is synonymous with barak [lightning] in the previous verse, since the letters z and r in Hebrew are occasionally interchangeable.  

And indeed, Soncino and other translations translate the word bazak as lightning.

The malbim says that bazak is like the fire of a furnace "that is seen for an instance and is gone instantly".

When the gemara in Hagiggah (13b) discusses the meaning of the word it uses the gold refining analogy that Rashi brings in his commentary.  Rashi there explains the process more in detail.  Artscroll note:

Rashi explains this analogy as follows: when a goldsmith wishes to purify a quantity of gold, he builds a coal fire...[and covers it with] a dome made of earthenware.  The earthenware dome has been made especially for this purpose and contains many holes.  As the gold is purifying, flames shoot (italics mine) up through these holes.  The flames appear in  all different colors.

Sounds like a laser to me!

So the Bazak is "pulverized" (כיתות) in the same way that the asheirah is "pulverized"  (כיתות).  The particles of the Bazak laser are floating around in a way that makes them there but not there in the same way that the pulverized ashes of teh asheirah tree are floating around making them there but not there.

It is bullet proof, but I found this interesting in addition to the halachic argument.