Is there significance to the number 4? Certainly it can be argued that several simultaneous attacks are a pretty strong statement, regardless of number.And we have a timeline here of most of the major attacks of recent years, and incidents from 1 to several attacks at once are reported.
But still, I was curious. So here we go a' Googling. And after several false starts, I found this:
Four qualities bestowed upon saints in Islam
Verse about “prophets, truthful, faithful and righteous”
refers to four qualities as the goal for believers
from the writings of Hazrat Mirza Ghulam Ahmad
. . .
We have translated below a lengthy explanation of this verse as given by Hazrat Mirza Ghulam Ahmad. It is absolutely clear from his explanation that the verse refers to the attainment of four kinds of qualities by saints in Islam.
. . .
First quality: receiving revelation
Firstly, matters of the unseen should, after supplication or by other means, be disclosed to him in such abundance, and many prophecies be fulfilled so clearly, that no other person could rival him in respect of abundance of quantity and clarity of condition. And as regards this abundance and clarity, it should be not only improbable, but impossible, that someone else could have a share of these qualities. That is to say, it should be entirely impossible that someone else could parallel or rival these qualities in terms of secrets of the unseen revealed, acceptance of his prayers and prior intimation of the same to him, and signs of support that appear in heaven and earth. And he should, by way of miracle and in an extraordinary manner, be granted such Divine knowledge of the unseen, luminous visions and heavenly support, as if a gigantic river were flowing and a glorious light descending from heaven and spreading on the earth; and these things should reach the stage where they appear to be miraculous and unequalled in their time. This excellence is called the excellence of prophethood.
Second quality: truth
The second excellence that is necessary as a sign for the leader of the saints and chief of the purified ones is the attainment of the higher understanding and knowledge of the Quran. It is necessary to remember that there is a lower, an average and a higher teaching of the Quran. The higher teaching abounds in so much light of knowledge, brightness of truth, true beauty, and virtue, that the lower or average ability cannot possibly reach it. Only the possessors of the purest nature, whose entirely luminous disposition draws light to itself, attain to these truths.
So the first stage of sidq (truthfulness) that they attain is aversion for worldly affairs and an instinctive dislike of what is vain. After this condition is firmly established, the second stage of sidq is reached which can be called zeal, enthusiasm and turning towards God. And after this state is thoroughly established, a third stage of sidq is attained which can be called the greatest transformation, an entire cutting off, personal love, and the rank of total self-effacement in Allah.
This having been deeply-rooted, the spirit of truth penetrates the human being, and all pure truths and matters of knowledge of a high order are revealed to him. There rises up in his heart, and pours forth from his lips, the most profound and deep knowledge of the Quran and points of the Shariah. And such secrets and subtleties of the religion are disclosed to him as are inaccessible to the intellects of the followers of customary and conventional knowledge. This is because he is inspired by God, and the holy spirit speaks within him. All inclinations to falsehood are cut out from within him because he learns from the spirit, speaks according to it, and by the spirit does he influence others.
In this state he is called siddiq (truthful) because the darkness of falsehood entirely leaves him, and is substituted by purity and the light of truth. The manifestation through him, at this stage, of truths and matters of knowledge of a high order is a sign of him. Having been fermented by the light of truth, his holy teaching astonishes the world. People are wonder-struck by his pious knowledge which stems from his self-effacement in Allah and knowledge of the truth. This quality is called the quality of siddiqiyya (lit. truthfulness).
It should be remembered that siddiq is one who both has a complete knowledge of the Divine truths and acts on them perfectly instinctively. For instance, he knows the true significance of matters such as Divine unity, obedience to God, love of God, the obtaining of complete riddance from worshipping others than God; the real meaning of devotion to God, sincerity, repentance; and the essence of moral virtues such as patience, trust in God, resignation to Him, effacement in Him, truthfulness, fidelity, forgiveness, modesty, honesty, trustworthiness, etc. And apart from having this knowledge, he is well-established on all these virtues.
Third quality: being a witness of faith
The third excellence granted to the great saints is the rank of shahadah. By this rank is meant that station where, by the strength of his faith, man acquires such a belief in God and in the Day of Judgment that it is as if he sees God with his own eyes. Then, with the blessing of this conviction, the effort and exertion of doing righteous deeds melts away, every Divinely-ordained fate appears sweet as honey to his heart, and each trial is seen by him as a reward.
Hence shaheed is one who, by the strength of his faith, beholds God, and enjoys like sweet honey the bitter fate ordained by Him. This is why he is called shaheed. This rank is a sign of the perfect believer.
Fourth quality: righteousness
There is also a fourth rank which is attained fully and completely by the perfect saints and the purified ones: the rank of salihin (lit. the righteous). A person is called salih when he becomes inwardly cleared and purified of all wickedness, and with the removal of all this putrid and filthy matter, the ecstasy of Divine worship and contemplation reaches the highest degree. For, just as the taste of the tongue is spoilt by physical illness, so is the sense of spiritual flavour vitiated by spiritual ailments; and a person thus afflicted feels no pleasure in Divine worship and contemplation, nor does he have any enthusiasm, zeal or urge for it. On the other hand, the perfect man is not only cleansed of all evil matter but this quality develops so much within him as to appear as a sign and miracle.
These are, in short, the four grades, to try to attain to which is the duty of every believer. The person who entirely lacks these, lacks faith. This is why in the Sura Fatiha the Glorious God has ordained for the Muslims this very prayer that they implore Him for all these virtues. This prayer is: “Guide us on the right path, the path of those upon whom You have bestowed favours”. This verse has been explained at the other place in the Holy Quran [4:69] where it is made clear that by those upon whom God has bestowed favours are meant the prophets, the siddiq, the shaheed, and the salih. The perfect man has all of these four qualities combined in him.”
— Tiryaq al-Qulub, in Ruhani Khaza’in, vol. 15, pages 417–423.
So, I dunno. 4 has significance in many ways, to many things:
Baseball: 4 bases
Beatles: 4 guys
Cars: 4 wheels
Compass: 4 points
Vivaldi, Hotel, "Sherry, Baby": Four Seasons
Apocolypse: 4 Horsemen
And many more. So does this mean anything? Not likely. But still, 4 of something happening with any simultaneity is pretty interesting, and in these cases, pretty disastrous.