Can we know that Moshiach is coming? Can we definitively say that he's coming now and that the rumors are true?
I present you with the following information, and allow you to conclude what you will.
The Yalkut Shimoni (ישעיה ס) states as follows:
שנו רבותינו בשעה שמלך המשיח בא עומד על גג בית המקדש והוא משמיע להם לישראל ואומר ענוים הגיע זמן גאולתכם ואם אין אתם מאמינים ראו באורי שזרח עליכם.
Our Rabbis taught; When the king Moshiach comes, he stands on the roof of the Beis Hamikdash (Temple) and he makes heard to the people of Israel and says, "Humble ones, the time for your redemption has arrived. And if you do not believe, see my light that shines upon you."
Can we imagine this? Moshiach has come, and he is standing on the rebuilt third Temple. He cries out to the people of Israel that the time for redemption has arrived. And he ends off his statement by saying, that if you do not believe, then see my spiritual light that is shining.
I don't know about you, but if I was standing there I would have to be nuts not to believe! Moshiach himself is standing on the Beis Hamikdash announcing the geulah!!! What is the meaning of this medrash?
I lead you to another piece a little farther on in the yalkut (ישעיה ס"ג) that I saw and was astounded by.
רבי שמואל מתני בשם רבי ירמיה אם יאמר לך אדם מתי קץ הגאולה אל תאמן שנאמר כי יום נקם בלבי - לבא לפומא לא גלי פומא למאן גלי
Rebbe Shmuel taught in the name of Rebbe Yirmiyah; if someone tells you when the final redemption will be, do not believe them as the verse says, "The day of retribution is in my heart." The heart did not reveal to the mouth, so to whom can the mouth reveal?
רבי ברכיה ורבי סימון בשם רבי יהושע בן לוי שלש סימנין סמנתי לך בקברו של משה שנאמר ויקבור אתו בגיא וגו' וסוף לא ידע איש את קבורתו, על הקץ שנאמר סתום וחתום הדברים על אחת כמה וכמה
Rebbe Berechyah and Rebbe Simon said in the name of Rebbe Yehoshua ben Levi; Three signs were given for the location of the grave of Moshe Rabenu, zs'kl, as the verse says, "He buried him in the glen etc..." and in the end, the verse says that no one knows where he is buried; In regards to the final redemption [there are no signs, but rather] the verse says, "Close and seal the matter," certainly [one can not know when it will be].
At first glance, this is very discouraging, as it clearly indicates that we can give up trying to figure out when Moshiach will come. But when I saw this for the first time a few weeks ago, I had recently learned a very important Gemara in Sotah (דף י"ג-י"ד) which is a continuation of this yalkut, and I think it sheds light on the whole matter.
אמר ר' ברכיה סימן בתוך סימן ואפילו הכי ולא ידע איש את קבורתו. וכבר שלחה מלכות הרשעה אצל גסטרא של בית פעור הראנו היכן משה קבור. עמדו למעלה נדמה להם למטה. למטה, נדמה להם למעלה. נחלקו לשתי כיתות, אותן שעומדים למעלה נדמה להם למטה, למטה נדמה להם למעלה, לקיים מה שנאמר ולא ידע איש את קבורתו
Rebbe Berechyah said, a sign inside of a sign [was given for the grave of Moshe Rabenu] and nevertheless "No man knows where he is buried." And the evil kingdom already sent to the leader of the area of Beis Peor asking to reveal where where Moshe Rabenu was buried. They stood at an elevation [where Moshe Rabenu was supposed to have been buried]. It seemed that the burial site was below. They went below and it seemed that the site was above. They split into two camps. Those that stood above, it seemed to be below. Those that stood below, to them it seemed the site was above. This fulfills the verse, "And no man knows of his burial."
The first piece of information that we need to understand this is that the word דעת - knowledge - is different from חכמה and בינה. Whereas both חכמה and בינה represent abstract knowledge, דעת represents intimate, experiential knowledge. Translated simply, you can explain the concept of color to a blind person to the point that he will perhaps understand (with חכמה and בינה) what you are talking about. But until he can see, he will not truly have the דעת - experiential and intimate knowledge. It will just remain theory.
The messengers of the evil kingdom could have a theoretical knowledge of where the burial plot of Moshe Rabenu was, but for some supernatural reason, it would be impossible for them to experience the place. Hence the verse, "ולא ידע איש את קבורתו" - "And no man knows of his burial."
Now let us take this information back to the second piece of the Yalkut. There, we are told that one can not know of the time of redemption, just as one can not know where Moshe Rabenu is buried. The connection is astounding! We can theorize with our חכמה and בינה as to when Moshiach will come, but we can actually be there and not know it! It is something the heart (לב = בינה) knows, but has not communicated to the mouth (mouth is the expression of דעת)! We can be in one temporal place (תשס"ח 5768) and believe that we have reached the time, yet every time we try to experience it with our דעת it will seem to be some other time (perhaps 5769 תשס"ט?). Or just when we think we "know" who the final story is about (George is גוג? America is מגוג?) things take a sudden turn and we realize we may not know. (Maybe Putin is גוג? Maybe Russia is מגוג?)
This all brings us back to the first Yalkut. Moshiach is standing on the Beis Hamikdash telling us he has come and the Geulah is here, and we don't believe?! We don't know? Not until the light of Hashem shines on us and enlightens us with the transcendental knowledge of Moshiach's true arrival and Hashem's Ultimate Good, will we truly have this knowledge.
When we try to bring our knowledge from חכמה and בינה (theoretical) to the level of דעת (defined), we have confined all the possibilities and chosen one. But since we are dealing with something that is by definition unknowable, it always seems to be somewhere else. That's why when they were below, Moshe's grave seemed to be above and vice versa. They tried to bring out their חכמה to דעת but this was impossible. The same thing happens when we try to put our finger on Moshiach. Since it is by definition unknowable, as soon as we define it, it is lost and appears to be elsewhere.
This is why Chazal tell us אין בן-דוד בא אלא בהיסח-הדעת - Moshiach can't come until we have a hesech hada'as - a break from our דעת, our efforts at defining. We can't stop thinking about Moshiach, because we need the אתערותא דלתתא the awakening from below to bring it about from Above.
Nevertheless, as long as we think about it, we limit our options and lose the real option - it always looks like it's somewhere else. That's why we need the היסח הדעת - the break in defining thought.
Said in a different way, כתר, which is the highest sefirah, represents transcendence - reaching above our thinking into the higher world. This is what we are aiming for, this is the time of Moshiach. Keser can not exist at the same time as Da'as. Keser represents indeterminacy and entering the domain of the unknown. Da'as represents choosing and defining and knowing. In order to enter the domain of Keser we need to be released from da'as. This is why Moshiach can only come with a היסח הדעת - a break from trying to define.
This is also why the gemara gives us three separate events in three separate years.
Sixth year - קולות - rumors of Moshiach
Seventh year - מלחמות - wars
Eighth year - בן דוד בא - Moshiach comes
The rumors can not coincide with Moshiach's arrival. Something will happen that will cause us to 'space out.' Only then will he come. May it be soon.